From 226c550ffafc08d3d34d4a92882ed3729124faa0 Mon Sep 17 00:00:00 2001
From: Slavi Pantaleev <slavi@devture.com>
Date: Thu, 15 Sep 2022 07:05:25 +0300
Subject: [PATCH] Add support for stream writer Synapse workers

As stream writer workers are also powered by the `generic_worker`
Synapse app, this necessitated that we provide means for distinguishing
between them and regular `generic_workers`.

I've also taken the time to optimize nginx configuration generation
(more Jinja2 macro usage, less duplication).

Worker names have also changed.
Workers are now named sequentially like this:
- `matrix-synapse-worker-0-generic`
- `matrix-synapse-worker-1-stream-writer-typing`
- `matrix-synapse-worker-2-pusher`

instead of `matrix-synapse-worker_generic_worker-18111` (indexed with a
port number).

People who modify `matrix_synapse_workers_enabled_list` directly will
need to adjust their configuration.
---
 CHANGELOG.md                                  |  39 ++++++
 ...configuring-playbook-prometheus-grafana.md |   8 +-
 group_vars/matrix_servers                     |   7 +
 roles/matrix-nginx-proxy/defaults/main.yml    |   5 +
 .../nginx/conf.d/matrix-synapse.conf.j2       | 125 +++++++++++-------
 .../templates/prometheus.yml.j2               |   5 +-
 roles/matrix-synapse/defaults/main.yml        | 112 ++++++++++++++--
 roles/matrix-synapse/tasks/init.yml           |  10 +-
 .../tasks/synapse/workers/init.yml            |  50 ++++++-
 .../inject_systemd_services_for_worker.yml    |  19 ---
 .../synapse/workers/util/inject_worker.yml    |  65 +++++++++
 .../workers/util/setup_files_for_worker.yml   |  10 +-
 .../matrix-synapse/tasks/validate_config.yml  |   5 +
 .../templates/synapse/homeserver.yaml.j2      |   8 +-
 .../external_prometheus.yml.example.j2        |   7 +-
 .../systemd/matrix-synapse-worker.service.j2  |   2 +-
 .../synapse/systemd/matrix-synapse.service.j2 |   2 +-
 .../templates/synapse/worker.yaml.j2          |  36 +++--
 roles/matrix-synapse/vars/main.yml            |  55 ++++++++
 19 files changed, 449 insertions(+), 121 deletions(-)
 delete mode 100644 roles/matrix-synapse/tasks/synapse/workers/util/inject_systemd_services_for_worker.yml
 create mode 100644 roles/matrix-synapse/tasks/synapse/workers/util/inject_worker.yml

diff --git a/CHANGELOG.md b/CHANGELOG.md
index df4957eb..2b9b149e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,42 @@
+# 2022-09-15
+
+## (Potential Backward Compatibility Break) Major changes to Synapse workers
+
+People who are interested in running a Synapse worker setup should know that **our Synapse worker implementation is much more powerful now**:
+
+- we've added [Stream writers support](#stream-writers-support)
+- see the [Potential Backward Incompatibilities after these Synapse worker changes](#potential-backward-incompatibilities-after-these-synapse-worker-changes)
+
+### Stream writers support
+
+From now on, the playbook lets you easily set up various [stream writer workers](https://matrix-org.github.io/synapse/latest/workers.html#stream-writers) which can handle different streams (`events` stream; `typing` URL endpoints, `to_device` URL endpoints, `account_data` URL endpoints, `receipts` URL endpoints, `presence` URL endpoints). All of this work was previously handled by the main Synapse process, but can now be offloaded to stream writer worker processes.
+
+If you're using `matrix_synapse_workers_preset: one-of-each`, you'll automatically get 6 additional workers (one for each of the above stream types). Our `little-federation-helper` preset (meant to be quite minimal and focusing in improved federation performance) does not include stream writer workers.
+
+If you'd like to customize the number of workers we also make that possible using these variables:
+
+```yaml
+# Synapse only supports more than 1 worker for the `events` stream.
+# All other streams can utilize either 0 or 1 workers, not more than that.
+matrix_synapse_workers_stream_writer_events_stream_workers_count: 5
+matrix_synapse_workers_stream_writer_typing_stream_workers_count: 1
+matrix_synapse_workers_stream_writer_to_device_stream_workers_count: 1
+matrix_synapse_workers_stream_writer_account_data_stream_workers_count: 1
+matrix_synapse_workers_stream_writer_receipts_stream_workers_count: 1
+matrix_synapse_workers_stream_writer_presence_stream_workers_count: 1
+```
+
+### Potential Backward Incompatibilities after these Synapse worker changes
+
+Below we'll discuss **potential backward incompatibilities**.
+
+- **Worker names** (container names, systemd services, worker configuration files) **have changed**. Workers are now labeled sequentially (e.g. `matrix-synapse-worker_generic_worker-18111` -> `matrix-synapse-worker-generic-0`). The playbook will handle these changes automatically.
+
+- **Metric endpoints have also changed** (`/metrics/synapse/worker/generic_worker-18111` -> `/metrics/synapse/worker/generic-worker-0`). If you're [collecting metrics to an external Prometheus server](docs/configuring-playbook-prometheus-grafana.md#collecting-metrics-to-an-external-prometheus-server), consider revisiting our [Collecting Synapse worker metrics to an external Prometheus server](docs/configuring-playbook-prometheus-grafana.md#collecting-synapse-worker-metrics-to-an-external-prometheus-server) docs and updating your Prometheus configuration. **If you're collecting metrics to the integrated Prometheus server** (not enabled by default), **your Prometheus configuration will be updated automatically**. Old data (from before this change) may stick around though.
+
+- **the format of `matrix_synapse_workers_enabled_list` has changed**. You were never advised to use this variable for directly creating workers (we advise people to control workers using `matrix_synapse_workers_preset` or by tweaking `matrix_synapse_workers_*_workers_count` variables only), but some people may have started using the `matrix_synapse_workers_enabled_list` variable to gain more control over workers. If you're one of them, you'll need to adjust its value. See `roles/matrix-synapse/defaults/main.yml` for more information on the new format. The playbook will also do basic validation and complain if you got something wrong.
+
+
 # 2022-09-09
 
 ## Cactus Comments support
diff --git a/docs/configuring-playbook-prometheus-grafana.md b/docs/configuring-playbook-prometheus-grafana.md
index b2878c12..f86566a9 100644
--- a/docs/configuring-playbook-prometheus-grafana.md
+++ b/docs/configuring-playbook-prometheus-grafana.md
@@ -90,11 +90,11 @@ matrix_nginx_proxy_proxy_matrix_metrics_additional_user_location_configuration_b
 
 Using `matrix_nginx_proxy_proxy_matrix_metrics_additional_user_location_configuration_blocks` only takes effect if `matrix_nginx_proxy_proxy_matrix_metrics_enabled: true` (see above).
 
-Note : The playbook will hash the basic_auth password for you on setup. Thus, you need to give the plain-text version of the password as a variable. 
+Note : The playbook will hash the basic_auth password for you on setup. Thus, you need to give the plain-text version of the password as a variable.
 
 ### Collecting Synapse worker metrics to an external Prometheus server
 
-If you are using workers (`matrix_synapse_workers_enabled: true`) and have enabled `matrix_synapse_metrics_proxying_enabled` as described above, the playbook will also automatically expose all Synapse worker threads' metrics to `https://matrix.DOMAIN/metrics/synapse/worker/TYPE-ID`, where `TYPE` corresponds to the type and `ID` to the instanceId of a worker as exemplified in `matrix_synapse_workers_enabled_list`.
+If you are using workers (`matrix_synapse_workers_enabled: true`) and have enabled `matrix_synapse_metrics_proxying_enabled` as described above, the playbook will also automatically expose all Synapse worker threads' metrics to `https://matrix.DOMAIN/metrics/synapse/worker/ID`, where `ID` corresponds to the worker `id` as exemplified in `matrix_synapse_workers_enabled_list`.
 
 The playbook also generates an exemplary config file (`/matrix/synapse/external_prometheus.yml.template`) with all the correct paths which you can copy to your Prometheus server and adapt to your needs. Make sure to edit the specified `password_file` path and contents and path to your `synapse-v2.rules`.
 It will look a bit like this:
@@ -111,8 +111,8 @@ scrape_configs:
         labels:
           job: "master"
           index: 1
-  - job_name: 'synapse-generic_worker-1'
-    metrics_path: /metrics/synapse/worker/generic_worker-18111
+  - job_name: 'matrix-synapse-synapse-worker-generic-worker-0'
+    metrics_path: /metrics/synapse/worker/generic-worker-0
     scheme: https
     basic_auth:
       username: prometheus
diff --git a/group_vars/matrix_servers b/group_vars/matrix_servers
index c0d831e1..e891a3d9 100755
--- a/group_vars/matrix_servers
+++ b/group_vars/matrix_servers
@@ -1760,6 +1760,11 @@ matrix_nginx_proxy_synapse_workers_enabled: "{{ matrix_synapse_workers_enabled }
 matrix_nginx_proxy_synapse_workers_list: "{{ matrix_synapse_workers_enabled_list }}"
 matrix_nginx_proxy_synapse_generic_worker_client_server_locations: "{{ matrix_synapse_workers_generic_worker_client_server_endpoints }}"
 matrix_nginx_proxy_synapse_generic_worker_federation_locations: "{{ matrix_synapse_workers_generic_worker_federation_endpoints }}"
+matrix_nginx_proxy_synapse_stream_writer_typing_stream_worker_client_server_locations: "{{ matrix_synapse_workers_stream_writer_typing_stream_worker_client_server_endpoints }}"
+matrix_nginx_proxy_synapse_stream_writer_to_device_stream_worker_client_server_locations: "{{ matrix_synapse_workers_stream_writer_to_device_stream_worker_client_server_endpoints }}"
+matrix_nginx_proxy_synapse_stream_writer_account_data_stream_worker_client_server_locations: "{{ matrix_synapse_workers_stream_writer_account_data_stream_worker_client_server_endpoints }}"
+matrix_nginx_proxy_synapse_stream_writer_receipts_stream_worker_client_server_locations: "{{ matrix_synapse_workers_stream_writer_receipts_stream_worker_client_server_endpoints }}"
+matrix_nginx_proxy_synapse_stream_writer_presence_stream_worker_client_server_locations: "{{ matrix_synapse_workers_stream_writer_presence_stream_worker_client_server_endpoints }}"
 matrix_nginx_proxy_synapse_media_repository_locations: "{{matrix_synapse_workers_media_repository_endpoints|default([]) }}"
 matrix_nginx_proxy_synapse_user_dir_locations: "{{ matrix_synapse_workers_user_dir_endpoints|default([]) }}"
 
@@ -1767,6 +1772,8 @@ matrix_nginx_proxy_systemd_wanted_services_list: |
   {{
     ['matrix-' + matrix_homeserver_implementation + '.service']
     +
+    (matrix_synapse_webserving_workers_systemd_services_list if matrix_homeserver_implementation == 'synapse' and matrix_synapse_workers_enabled)
+    +
     (['matrix-corporal.service'] if matrix_corporal_enabled else [])
     +
     (['matrix-ma1sd.service'] if matrix_ma1sd_enabled else [])
diff --git a/roles/matrix-nginx-proxy/defaults/main.yml b/roles/matrix-nginx-proxy/defaults/main.yml
index a7484215..88c99ea9 100644
--- a/roles/matrix-nginx-proxy/defaults/main.yml
+++ b/roles/matrix-nginx-proxy/defaults/main.yml
@@ -623,6 +623,11 @@ matrix_nginx_proxy_synapse_workers_enabled: false
 matrix_nginx_proxy_synapse_workers_list: []
 matrix_nginx_proxy_synapse_generic_worker_client_server_locations: []
 matrix_nginx_proxy_synapse_generic_worker_federation_locations: []
+matrix_nginx_proxy_synapse_stream_writer_typing_stream_worker_client_server_locations: []
+matrix_nginx_proxy_synapse_stream_writer_to_device_stream_worker_client_server_locations: []
+matrix_nginx_proxy_synapse_stream_writer_account_data_stream_worker_client_server_locations: []
+matrix_nginx_proxy_synapse_stream_writer_receipts_stream_worker_client_server_locations: []
+matrix_nginx_proxy_synapse_stream_writer_presence_stream_worker_client_server_locations: []
 matrix_nginx_proxy_synapse_media_repository_locations: []
 matrix_nginx_proxy_synapse_user_dir_locations: []
 
diff --git a/roles/matrix-nginx-proxy/templates/nginx/conf.d/matrix-synapse.conf.j2 b/roles/matrix-nginx-proxy/templates/nginx/conf.d/matrix-synapse.conf.j2
index 81e31a7c..bbce7462 100644
--- a/roles/matrix-nginx-proxy/templates/nginx/conf.d/matrix-synapse.conf.j2
+++ b/roles/matrix-nginx-proxy/templates/nginx/conf.d/matrix-synapse.conf.j2
@@ -1,23 +1,52 @@
 #jinja2: lstrip_blocks: "True"
 
 {% set generic_workers = matrix_nginx_proxy_synapse_workers_list | selectattr('type', 'equalto', 'generic_worker') | list %}
+{% set stream_writer_typing_stream_workers = matrix_nginx_proxy_synapse_workers_list | selectattr('type', 'equalto', 'stream_writer') | selectattr('stream_writer_stream', 'equalto', 'typing') | list %}
+{% set stream_writer_to_device_stream_workers = matrix_nginx_proxy_synapse_workers_list | selectattr('type', 'equalto', 'stream_writer') | selectattr('stream_writer_stream', 'equalto', 'to_device') | list %}
+{% set stream_writer_account_data_stream_workers = matrix_nginx_proxy_synapse_workers_list | selectattr('type', 'equalto', 'stream_writer') | selectattr('stream_writer_stream', 'equalto', 'account_data') | list %}
+{% set stream_writer_receipts_stream_workers = matrix_nginx_proxy_synapse_workers_list | selectattr('type', 'equalto', 'stream_writer') | selectattr('stream_writer_stream', 'equalto', 'receipts') | list %}
+{% set stream_writer_presence_stream_workers = matrix_nginx_proxy_synapse_workers_list | selectattr('type', 'equalto', 'stream_writer') | selectattr('stream_writer_stream', 'equalto', 'presence') | list %}
 {% set media_repository_workers = matrix_nginx_proxy_synapse_workers_list | selectattr('type', 'equalto', 'media_repository') | list %}
 {% set user_dir_workers = matrix_nginx_proxy_synapse_workers_list | selectattr('type', 'equalto', 'user_dir') | list %}
+
+{% macro render_worker_upstream(name, workers, matrix_nginx_proxy_enabled) %}
+{% if workers | length > 0 %}
+	upstream {{ name }} {
+		{% for worker in workers %}
+			{% if matrix_nginx_proxy_enabled %}
+				server "{{ worker.name }}:{{ worker.port }}";
+			{% else %}
+				server "127.0.0.1:{{ worker.port }}";
+			{% endif %}
+		{% endfor %}
+	}
+{% endif %}
+{% endmacro %}
+
+{% macro render_locations_to_upstream(locations, upstream_name) %}
+	{% for location in locations %}
+	location ~ {{ location }} {
+		proxy_pass http://{{ upstream_name }}$request_uri;
+		proxy_set_header Host $host;
+	}
+	{% endfor %}
+{% endmacro %}
+
 {% if matrix_nginx_proxy_synapse_workers_enabled %}
 	{% if matrix_nginx_proxy_synapse_cache_enabled %}
     	proxy_cache_path  {{ matrix_nginx_proxy_synapse_cache_path }} levels=1:2 keys_zone={{ matrix_nginx_proxy_synapse_cache_keys_zone_name }}:{{ matrix_nginx_proxy_synapse_cache_keys_zone_size }} inactive={{ matrix_nginx_proxy_synapse_cache_inactive_time }} max_size={{ matrix_nginx_proxy_synapse_cache_max_size_mb }}m;
 	{% endif %}
 	# Round Robin "upstream" pools for workers
 
-	{% if generic_workers %}
-	upstream generic_worker_upstream {
+	{% if generic_workers |length > 0 %}
+	upstream generic_workers_upstream {
 		# ensures that requests from the same client will always be passed
 		# to the same server (except when this server is unavailable)
 		hash $http_x_forwarded_for;
 
 		{% for worker in generic_workers %}
 			{% if matrix_nginx_proxy_enabled %}
-				server "matrix-synapse-worker-{{ worker.type }}-{{ worker.instanceId }}:{{ worker.port }}";
+				server "{{ worker.name }}:{{ worker.port }}";
 			{% else %}
 				server "127.0.0.1:{{ worker.port }}";
 			{% endif %}
@@ -25,29 +54,15 @@
 	}
 	{% endif %}
 
-	{% if media_repository_workers %}
-	upstream media_repository_upstream {
-		{% for worker in media_repository_workers %}
-			{% if matrix_nginx_proxy_enabled %}
-				server "matrix-synapse-worker-{{ worker.type }}-{{ worker.instanceId }}:{{ worker.port }}";
-			{% else %}
-				server "127.0.0.1:{{ worker.port }}";
-			{% endif %}
-		{% endfor %}
-	}
-	{% endif %}
+	{{ render_worker_upstream('stream_writer_typing_stream_workers_upstream', stream_writer_typing_stream_workers, matrix_nginx_proxy_enabled) }}
+	{{ render_worker_upstream('stream_writer_to_device_stream_workers_upstream', stream_writer_to_device_stream_workers, matrix_nginx_proxy_enabled) }}
+	{{ render_worker_upstream('stream_writer_account_data_stream_workers_upstream', stream_writer_account_data_stream_workers, matrix_nginx_proxy_enabled) }}
+	{{ render_worker_upstream('stream_writer_receipts_stream_workers_upstream', stream_writer_receipts_stream_workers, matrix_nginx_proxy_enabled) }}
+	{{ render_worker_upstream('stream_writer_presence_stream_workers_upstream', stream_writer_presence_stream_workers, matrix_nginx_proxy_enabled) }}
 
-	{% if user_dir_workers %}
-	upstream user_dir_upstream {
-		{% for worker in user_dir_workers %}
-			{% if matrix_nginx_proxy_enabled %}
-				server "matrix-synapse-worker-{{ worker.type }}-{{ worker.instanceId }}:{{ worker.port }}";
-			{% else %}
-				server "127.0.0.1:{{ worker.port }}";
-			{% endif %}
-		{% endfor %}
-	}
-	{% endif %}
+	{{ render_worker_upstream('media_repository_workers_upstream', media_repository_workers, matrix_nginx_proxy_enabled) }}
+
+	{{ render_worker_upstream('user_dir_workers_upstream', user_dir_workers, matrix_nginx_proxy_enabled) }}
 {% endif %}
 
 server {
@@ -65,21 +80,41 @@ server {
 	{% if matrix_nginx_proxy_synapse_workers_enabled %}
 		{# Workers redirects BEGIN #}
 
-		{% if generic_workers %}
+		{% if generic_workers | length > 0 %}
 			# https://github.com/matrix-org/synapse/blob/master/docs/workers.md#synapseappgeneric_worker
-			{% for location in matrix_nginx_proxy_synapse_generic_worker_client_server_locations %}
-			location ~ {{ location }} {
-				proxy_pass http://generic_worker_upstream$request_uri;
-				proxy_set_header Host $host;
-			}
-			{% endfor %}
+			{{ render_locations_to_upstream(matrix_nginx_proxy_synapse_generic_worker_client_server_locations, 'generic_workers_upstream') }}
+		{% endif %}
+
+		{% if stream_writer_typing_stream_workers | length > 0 %}
+			# https://matrix-org.github.io/synapse/latest/workers.html#the-typing-stream
+			{{ render_locations_to_upstream(matrix_nginx_proxy_synapse_stream_writer_typing_stream_worker_client_server_locations, 'stream_writer_typing_stream_workers_upstream') }}
+		{% endif %}
+
+		{% if stream_writer_to_device_stream_workers | length > 0 %}
+			# https://matrix-org.github.io/synapse/latest/workers.html#the-to_device-stream
+			{{ render_locations_to_upstream(matrix_nginx_proxy_synapse_stream_writer_to_device_stream_worker_client_server_locations, 'stream_writer_to_device_stream_workers_upstream') }}
+		{% endif %}
+
+		{% if stream_writer_account_data_stream_workers | length > 0 %}
+			# https://matrix-org.github.io/synapse/latest/workers.html#the-account_data-stream
+			{{ render_locations_to_upstream(matrix_nginx_proxy_synapse_stream_writer_account_data_stream_worker_client_server_locations, 'stream_writer_account_data_stream_workers_upstream') }}
 		{% endif %}
 
-		{% if media_repository_workers %}
+		{% if stream_writer_receipts_stream_workers | length > 0 %}
+			# https://matrix-org.github.io/synapse/latest/workers.html#the-receipts-stream
+			{{ render_locations_to_upstream(matrix_nginx_proxy_synapse_stream_writer_receipts_stream_worker_client_server_locations, 'stream_writer_receipts_stream_workers_upstream') }}
+		{% endif %}
+
+		{% if stream_writer_presence_stream_workers | length > 0 %}
+			# https://matrix-org.github.io/synapse/latest/workers.html#the-presence-stream
+			{{ render_locations_to_upstream(matrix_nginx_proxy_synapse_stream_writer_presence_stream_worker_client_server_locations, 'stream_writer_presence_stream_workers_upstream') }}
+		{% endif %}
+
+		{% if media_repository_workers | length > 0 %}
 			# https://github.com/matrix-org/synapse/blob/master/docs/workers.md#synapseappmedia_repository
 			{% for location in matrix_nginx_proxy_synapse_media_repository_locations %}
 			location ~ {{ location }} {
-				proxy_pass http://media_repository_upstream$request_uri;
+				proxy_pass http://media_repository_workers_upstream$request_uri;
 				proxy_set_header Host $host;
 
 				client_body_buffer_size 25M;
@@ -97,15 +132,10 @@ server {
 			{% endfor %}
 		{% endif %}
 
-		{% if user_dir_workers %}
+		{% if user_dir_workers | length > 0 %}
 			# FIXME: obsolete if matrix_nginx_proxy_proxy_matrix_user_directory_search_enabled is set
 			# https://github.com/matrix-org/synapse/blob/master/docs/workers.md#synapseappuser_dir
-			{% for location in matrix_nginx_proxy_synapse_user_dir_locations %}
-			location ~ {{ location }} {
-				proxy_pass http://user_dir_upstream$request_uri;
-				proxy_set_header Host $host;
-			}
-			{% endfor %}
+			{{ render_locations_to_upstream(matrix_nginx_proxy_synapse_user_dir_locations, 'user_dir_workers_upstream') }}
 		{% endif %}
 		{# Workers redirects END #}
 	{% endif %}
@@ -150,20 +180,15 @@ server {
 	gzip_types text/plain application/json;
 
 	{% if matrix_nginx_proxy_synapse_workers_enabled %}
-		{% if generic_workers %}
+		{% if generic_workers | length > 0 %}
 			# https://github.com/matrix-org/synapse/blob/master/docs/workers.md#synapseappgeneric_worker
-			{% for location in matrix_nginx_proxy_synapse_generic_worker_federation_locations %}
-			location ~ {{ location }} {
-				proxy_pass http://generic_worker_upstream$request_uri;
-				proxy_set_header Host $host;
-			}
-			{% endfor %}
+			{{ render_locations_to_upstream(matrix_nginx_proxy_synapse_generic_worker_federation_locations, 'generic_workers_upstream') }}
 		{% endif %}
-		{% if media_repository_workers %}
+		{% if media_repository_workers | length > 0 %}
 			# https://github.com/matrix-org/synapse/blob/master/docs/workers.md#synapseappmedia_repository
 			{% for location in matrix_nginx_proxy_synapse_media_repository_locations %}
 			location ~ {{ location }} {
-				proxy_pass http://media_repository_upstream$request_uri;
+				proxy_pass http://media_repository_workers_upstream$request_uri;
 				proxy_set_header Host $host;
 
 				client_body_buffer_size 25M;
diff --git a/roles/matrix-prometheus/templates/prometheus.yml.j2 b/roles/matrix-prometheus/templates/prometheus.yml.j2
index f3262f48..628f4f4f 100644
--- a/roles/matrix-prometheus/templates/prometheus.yml.j2
+++ b/roles/matrix-prometheus/templates/prometheus.yml.j2
@@ -37,11 +37,12 @@ scrape_configs:
         index: 0
   {% for worker in matrix_prometheus_scraper_synapse_workers_enabled_list %}
   {% if worker.metrics_port != 0 %}
-    - targets: ['matrix-synapse-worker-{{ worker.type }}-{{ worker.instanceId }}:{{ worker.metrics_port }}']
+    - targets: ['{{ worker.name }}:{{ worker.metrics_port }}']
       labels:
         instance: {{ matrix_domain }}
+		worker_id: {{ worker.id }}
         job: {{ worker.type }}
-        index: {{ worker.instanceId }}
+		app: {{ worker.app }}
   {% endif %}
   {% endfor %}
   {% endif %}
diff --git a/roles/matrix-synapse/defaults/main.yml b/roles/matrix-synapse/defaults/main.yml
index a7dab5b6..4213c4f1 100644
--- a/roles/matrix-synapse/defaults/main.yml
+++ b/roles/matrix-synapse/defaults/main.yml
@@ -398,6 +398,12 @@ matrix_synapse_workers_presets:
     federation_sender_workers_count: 1
     media_repository_workers_count: 0
     user_dir_workers_count: 0
+    stream_writer_events_stream_workers_count: 0
+    stream_writer_typing_stream_workers_count: 0
+    stream_writer_to_device_stream_workers_count: 0
+    stream_writer_account_data_stream_workers_count: 0
+    stream_writer_receipts_stream_workers_count: 0
+    stream_writer_presence_stream_workers_count: 0
   one-of-each:
     generic_workers_count: 1
     pusher_workers_count: 1
@@ -409,6 +415,12 @@ matrix_synapse_workers_presets:
     # user_dir workers are deprecated since Synapse v1.59. This will be removed.
     # See: https://github.com/matrix-org/synapse/blob/v1.59.0/docs/upgrade.md#deprecation-of-the-synapseappappservice-and-synapseappuser_dir-worker-application-types
     user_dir_workers_count: 0
+    stream_writer_events_stream_workers_count: 1
+    stream_writer_typing_stream_workers_count: 1
+    stream_writer_to_device_stream_workers_count: 1
+    stream_writer_account_data_stream_workers_count: 1
+    stream_writer_receipts_stream_workers_count: 1
+    stream_writer_presence_stream_workers_count: 1
 
 # Controls whether the matrix-synapse container exposes the various worker ports
 # (see `port` and `metrics_port` in `matrix_synapse_workers_enabled_list`) outside of the container.
@@ -421,6 +433,71 @@ matrix_synapse_workers_generic_workers_count: "{{ matrix_synapse_workers_presets
 matrix_synapse_workers_generic_workers_port_range_start: 18111
 matrix_synapse_workers_generic_workers_metrics_range_start: 19111
 
+# matrix_synapse_workers_stream_writer_events_stream_workers_count controls how many stream writers that handle the `events` stream to spawn.
+# More than 1 worker is also supported of this type.
+matrix_synapse_workers_stream_writer_events_stream_workers_count: "{{ matrix_synapse_workers_presets[matrix_synapse_workers_preset]['stream_writer_events_stream_workers_count'] }}"
+
+# matrix_synapse_workers_stream_writer_typing_stream_workers_count controls how many stream writers that handle the `typing` stream to spawn.
+# The count of these workers can only be 0 or 1.
+matrix_synapse_workers_stream_writer_typing_stream_workers_count: "{{ matrix_synapse_workers_presets[matrix_synapse_workers_preset]['stream_writer_typing_stream_workers_count'] }}"
+
+# matrix_synapse_workers_stream_writer_to_device_stream_workers_count controls how many stream writers that handle the `to_device` stream to spawn.
+# The count of these workers can only be 0 or 1.
+matrix_synapse_workers_stream_writer_to_device_stream_workers_count: "{{ matrix_synapse_workers_presets[matrix_synapse_workers_preset]['stream_writer_to_device_stream_workers_count'] }}"
+
+# matrix_synapse_workers_stream_writer_account_data_stream_workers_count controls how many stream writers that handle the `account_data` stream to spawn.
+# The count of these workers can only be 0 or 1.
+matrix_synapse_workers_stream_writer_account_data_stream_workers_count: "{{ matrix_synapse_workers_presets[matrix_synapse_workers_preset]['stream_writer_account_data_stream_workers_count'] }}"
+
+# matrix_synapse_workers_stream_writer_receipts_stream_workers_count controls how many stream writers that handle the `receipts` stream to spawn.
+# The count of these workers can only be 0 or 1.
+matrix_synapse_workers_stream_writer_receipts_stream_workers_count: "{{ matrix_synapse_workers_presets[matrix_synapse_workers_preset]['stream_writer_receipts_stream_workers_count'] }}"
+
+# matrix_synapse_workers_stream_writer_presence_stream_workers_count controls how many stream writers that handle the `presence` stream to spawn.
+# The count of these workers can only be 0 or 1.
+matrix_synapse_workers_stream_writer_presence_stream_workers_count: "{{ matrix_synapse_workers_presets[matrix_synapse_workers_preset]['stream_writer_presence_stream_workers_count'] }}"
+
+# A list of stream writer workers to enable. This list is built automatically based on other variables.
+# You're encouraged to enable/disable stream writer workers by setting `matrix_synapse_workers_stream_writer_*_stream_workers_count` variables, instead of adjusting this list manually.
+matrix_synapse_workers_stream_writers: |
+  {{
+    []
+    +
+    ([{'stream': 'events'}] * matrix_synapse_workers_stream_writer_events_stream_workers_count | int)
+    +
+    ([{'stream': 'typing'}] * matrix_synapse_workers_stream_writer_typing_stream_workers_count | int)
+    +
+    ([{'stream': 'to_device'}] * matrix_synapse_workers_stream_writer_to_device_stream_workers_count | int)
+    +
+    ([{'stream': 'account_data'}] * matrix_synapse_workers_stream_writer_account_data_stream_workers_count | int)
+    +
+    ([{'stream': 'receipts'}] * matrix_synapse_workers_stream_writer_receipts_stream_workers_count | int)
+    +
+    ([{'stream': 'presence'}] * matrix_synapse_workers_stream_writer_presence_stream_workers_count | int)
+  }}
+
+# matrix_synapse_stream_writers populates the `stream_writers` Synapse configuration used when Synapse workers are in use (`matrix_synapse_workers_enabled`).
+# What you see below is an initial default value which will be adjusted at runtime based on the value of `matrix_synapse_workers_stream_writers`.
+# Adjusting this value manually is generally not necessary.
+#
+# It's tempting to initialize this like this:
+# matrix_synapse_stream_writers:
+#   - typing: []
+#   - events: []
+#   - to_device: []
+#   - account_data: []
+#   - receipts: []
+#   - presence: []
+# .. but Synapse does not like empty lists (see https://github.com/matrix-org/synapse/issues/13804)
+matrix_synapse_stream_writers: {}
+
+# `matrix_synapse_workers_stream_writer_workers_` variables control the port numbers of various stream writer workers
+# defined in `matrix_synapse_workers_stream_writers`.
+# It should be noted that not all of the background worker types will need to expose HTTP services, etc.
+matrix_synapse_workers_stream_writer_workers_http_port_range_start: 20011
+matrix_synapse_workers_stream_writer_workers_replication_port_range_start: 25011
+matrix_synapse_workers_stream_writer_workers_metrics_range_start: 19111
+
 # matrix_synapse_workers_pusher_workers_count can only be 0 or 1 for now.
 # More instances are not supported due to a playbook limitation having to do with keeping `pusher_instances` in `homeserver.yaml` updated.
 # See https://github.com/matrix-org/synapse/commit/ddfdf945064925eba761ae3748e38f3a1c73c328
@@ -463,25 +540,36 @@ matrix_synapse_workers_user_dir_workers_metrics_range_start: 19661
 # as certain workers can only be spawned just once.
 #
 # Each worker instance in the list defines the following fields:
-# - `type` - the type of worker (`generic_worker`, etc.)
-# - `instanceId` - a string that identifies the worker. The combination of (`type` + `instanceId`) represents the name of the worker and must be unique.
+# - `id` - a string that uniquely identifies the worker
+# - `name` - a string that will be used as the container and systemd service name
+# - `type` - the type of worker (`generic_worker`, `stream_writer`, `pusher`, etc.)
+# - `app` - the Synapse app (https://matrix-org.github.io/synapse/latest/workers.html#available-worker-applications) that powers this worker (`generic_worker`, `federation_sender`, etc.).
+#           The `app` usually matches the `type`, but not always. For example, `type = stream_writer` workers are served by the `generic_worker` type.
 # - `port` - an HTTP port where the worker listens for requests (can be `0` for workers that don't do HTTP request processing)
 # - `metrics_port` - an HTTP port where the worker exports Prometheus metrics
+# - `replication_port` - an HTTP port where the worker serves `replication` endpoints (used by stream writers, etc.)
+# - `webserving` - tells whether this type of worker serves web (client or federation) requests, so that it can be injected as a dependency to the reverse-proxy
 #
 # Example of what this needs to look like, if you're defining it manually:
 # matrix_synapse_workers_enabled_list:
-#   - { type: generic_worker, instanceId: '18111', port: 18111, metrics_port: 19111 }
-#   - { type: generic_worker, instanceId: '18112', port: 18112, metrics_port: 19112 }
-#   - { type: generic_worker, instanceId: '18113', port: 18113, metrics_port: 19113 }
-#   - { type: generic_worker, instanceId: '18114', port: 18114, metrics_port: 19114 }
-#   - { type: generic_worker, instanceId: '18115', port: 18115, metrics_port: 19115 }
-#   - { type: generic_worker, instanceId: '18116', port: 18116, metrics_port: 19116 }
-#   - { type: pusher, instanceId: '0', port: 0, metrics_port: 19200 }
-#   - { type: appservice, instanceId: '0', port: 0, metrics_port: 19300 }
-#   - { type: federation_sender, instanceId: '0', port: 0, metrics_port: 19400 }
-#   - { type: media_repository, instanceId: '18551', port: 18551, metrics_port: 19551 }
+#   - { 'id': 'generic-worker-0', 'name': 'matrix-synapse-worker-generic-0', 'type': 'generic_worker', 'app': 'generic_worker', 'port': 18111, 'metrics_port': 19111, 'webserving': true }
+#   - { 'id': 'generic-worker-1', 'name': 'matrix-synapse-worker-generic-1', 'type': 'generic_worker', 'app': 'generic_worker', 'port': 18112, 'metrics_port': 19112, 'webserving': true }
+#   - { 'id': 'generic-worker-2', 'name': 'matrix-synapse-worker-generic-2', 'type': 'generic_worker', 'app': 'generic_worker', 'port': 18113, 'metrics_port': 19113, 'webserving': true }
+#   - { 'id': 'generic-worker-3', 'name': 'matrix-synapse-worker-generic-3', 'type': 'generic_worker', 'app': 'generic_worker', 'port': 18114, 'metrics_port': 19114, 'webserving': true }
+#   - { 'id': 'generic-worker-4', 'name': 'matrix-synapse-worker-generic-4', 'type': 'generic_worker', 'app': 'generic_worker', 'port': 18115, 'metrics_port': 19115, 'webserving': true }
+#   - { 'id': 'generic-worker-5', 'name': 'matrix-synapse-worker-generic-5', 'type': 'generic_worker', 'app': 'generic_worker', 'port': 18116, 'metrics_port': 19116, 'webserving': true }
+#   - { 'id': 'stream-writer-0-events', 'name': 'matrix-synapse-worker-stream-writer-0-events', 'type': 'stream_writer', 'app': 'generic_worker', 'stream_writer_stream': 'events', 'port': 0, 'replication_port': 25011, metrics_port: 19111, 'webserving': false }
+#   - { 'id': 'stream-writer-1-typing', 'name': 'matrix-synapse-worker-stream-writer-1-typing', 'type': 'stream_writer', 'app': 'generic_worker', 'stream_writer_stream': 'typing', 'port': 20012, 'replication_port': 25012, metrics_port: 19112, 'webserving': true }
+#   - { 'id': 'pusher-0', 'name': 'matrix-synapse-worker-pusher-0', 'type': 'pusher', 'app': 'pusher', 'port': 0, 'metrics_port': 19200, 'webserving': false }
+#   - { 'id': 'appservice-0', 'name': 'matrix-synapse-worker-appservice-0', 'type': 'appservice', 'port': 0, 'metrics_port': 19300, 'webserving': false }
+#   - { 'id': 'federation-sender-0', 'name': 'matrix-synapse-worker-federation-sender-0', 'type': 'federation_sender', 'port': 0, 'metrics_port': 19400, 'webserving': false }
+#   - { 'id': 'media-repository-0', 'name': 'matrix-synapse-worker-media-repository-0', 'type': 'media_repository', 'port': 18551, 'metrics_port': 19551, 'webserving': true }
 matrix_synapse_workers_enabled_list: []
 
+# matrix_synapse_instance_map holds the instance map used for mapping worker names (for certain generic workers only!) to where they live (host, port which handles replication traffic).
+# This is populated automatically based on `matrix_synapse_workers_enabled_list` during runtime, so you're not required to tweak it manually.
+matrix_synapse_instance_map: {}
+
 # Redis information
 matrix_synapse_redis_enabled: false
 matrix_synapse_redis_host: ""
diff --git a/roles/matrix-synapse/tasks/init.yml b/roles/matrix-synapse/tasks/init.yml
index 77696bce..8610a33b 100644
--- a/roles/matrix-synapse/tasks/init.yml
+++ b/roles/matrix-synapse/tasks/init.yml
@@ -8,15 +8,15 @@
 
 # Unless `matrix_synapse_workers_enabled_list` is explicitly defined,
 # we'll generate it dynamically.
-- ansible.builtin.import_tasks: "{{ role_path }}/tasks/synapse/workers/init.yml"
+- ansible.builtin.include_tasks: "{{ role_path }}/tasks/synapse/workers/init.yml"
   when: "matrix_synapse_enabled and matrix_synapse_workers_enabled and matrix_synapse_workers_enabled_list|length == 0"
 
 - ansible.builtin.set_fact:
     matrix_systemd_services_list: "{{ matrix_systemd_services_list + ['matrix-synapse.service'] }}"
   when: matrix_synapse_enabled | bool
 
-- name: Ensure systemd services for workers are injected
-  ansible.builtin.include_tasks: "{{ role_path }}/tasks/synapse/workers/util/inject_systemd_services_for_worker.yml"
+- name: Ensure workers are injected into various places
+  ansible.builtin.include_tasks: "{{ role_path }}/tasks/synapse/workers/util/inject_worker.yml"
   with_items: "{{ matrix_synapse_workers_enabled_list }}"
   loop_control:
     loop_var: matrix_synapse_worker_details
@@ -65,9 +65,9 @@
         matrix_synapse_worker_nginx_metrics_configuration_block: |
           {% for worker in matrix_synapse_workers_enabled_list %}
           {% if worker.metrics_port != 0 %}
-          location /metrics/synapse/worker/{{ worker.type }}-{{ worker.instanceId }} {
+          location /metrics/synapse/worker/{{ worker.id }} {
             resolver 127.0.0.11 valid=5s;
-            set $backend "matrix-synapse-worker-{{ worker.type }}-{{ worker.instanceId }}:{{ worker.metrics_port }}";
+            set $backend "{{ worker.name }}:{{ worker.metrics_port }}";
             proxy_pass http://$backend/_synapse/metrics;
             proxy_set_header Host $host;
           }
diff --git a/roles/matrix-synapse/tasks/synapse/workers/init.yml b/roles/matrix-synapse/tasks/synapse/workers/init.yml
index 3aa61923..fe613e70 100644
--- a/roles/matrix-synapse/tasks/synapse/workers/init.yml
+++ b/roles/matrix-synapse/tasks/synapse/workers/init.yml
@@ -7,18 +7,47 @@
 - name: Build generic workers
   ansible.builtin.set_fact:
     worker:
+      id: "generic-worker-{{ item }}"
+      name: "matrix-synapse-worker-generic-{{ item }}"
       type: 'generic_worker'
-      instanceId: "{{ matrix_synapse_workers_generic_workers_port_range_start + item }}"
+      app: 'generic_worker'
+      webserving: true
       port: "{{ matrix_synapse_workers_generic_workers_port_range_start + item }}"
       metrics_port: "{{ matrix_synapse_workers_generic_workers_metrics_range_start + item }}"
   register: "matrix_synapse_workers_list_results_generic_workers"
   loop: "{{ range(0, matrix_synapse_workers_generic_workers_count | int) | list }}"
 
+- name: Build stream writer workers
+  ansible.builtin.set_fact:
+    worker:
+      id: "stream-writer-{{ item }}-{{ item.stream }}"
+      # Names must not include understores. Certain stream writer streams (to_device, account_data, ..) do, so we fix them up.
+      name: "matrix-synapse-worker-stream-writer-{{ idx }}-{{ item.stream | replace('_', '-') }}"
+      type: 'stream_writer'
+      app: "generic_worker"
+      webserving: "{{ item.stream in matrix_synapse_workers_webserving_stream_writer_types }}"
+      stream_writer_stream: "{{ item.stream }}"
+      port: "{{ matrix_synapse_workers_stream_writer_workers_http_port_range_start + idx }}"
+      replication_port: "{{ matrix_synapse_workers_stream_writer_workers_replication_port_range_start + idx }}"
+      metrics_port: "{{ matrix_synapse_workers_stream_writer_workers_metrics_range_start + idx }}"
+  register: "matrix_synapse_workers_list_results_stream_writer_workers"
+  loop: "{{ matrix_synapse_workers_stream_writers }}"
+  loop_control:
+    index_var: idx
+
+- name: Populate matrix_synapse_stream_writers from enabled stream writer workers list
+  ansible.builtin.set_fact:
+    matrix_synapse_stream_writers: "{{ matrix_synapse_stream_writers | combine ({item.ansible_facts.worker.stream_writer_stream: [item.ansible_facts.worker.name]}) }}"
+  with_items: "{{ matrix_synapse_workers_list_results_stream_writer_workers.results }}"
+
 - name: Build federation sender workers
   ansible.builtin.set_fact:
     worker:
+      id: "federation-sender-{{ item }}"
+      name: "matrix-synapse-worker-federation-sender-{{ item }}"
       type: 'federation_sender'
-      instanceId: "{{ item }}"
+      app: 'federation_sender'
+      webserving: false
       port: 0
       metrics_port: "{{ matrix_synapse_workers_federation_sender_workers_metrics_range_start + item }}"
   register: "matrix_synapse_workers_list_results_federation_sender_workers"
@@ -28,8 +57,11 @@
 - name: Build pusher workers
   ansible.builtin.set_fact:
     worker:
+      id: "pusher-{{ item }}"
+      name: "matrix-synapse-worker-pusher-{{ item }}"
       type: 'pusher'
-      instanceId: "{{ item }}"
+      app: 'pusher'
+      webserving: false
       port: 0
       metrics_port: "{{ matrix_synapse_workers_pusher_workers_metrics_range_start + item }}"
   register: "matrix_synapse_workers_list_results_pusher_workers"
@@ -39,8 +71,11 @@
 - name: Build appservice workers
   ansible.builtin.set_fact:
     worker:
+      id: "appservice-{{ item }}"
+      name: "matrix-synapse-worker-appservice-{{ item }}"
       type: 'appservice'
-      instanceId: "{{ item }}"
+      app: 'appservice'
+      webserving: false
       port: 0
       metrics_port: "{{ matrix_synapse_workers_appservice_workers_metrics_range_start + item }}"
   register: "matrix_synapse_workers_list_results_appservice_workers"
@@ -49,8 +84,11 @@
 - name: Build media_repository workers
   ansible.builtin.set_fact:
     worker:
+      id: "media-repository-{{ item }}"
+      name: "matrix-synapse-worker-media-repository-{{ item }}"
       type: 'media_repository'
-      instanceId: "{{ matrix_synapse_workers_media_repository_workers_port_range_start + item }}"
+      app: 'media_repository'
+      webserving: true
       port: "{{ matrix_synapse_workers_media_repository_workers_port_range_start + item }}"
       metrics_port: "{{ matrix_synapse_workers_media_repository_workers_metrics_range_start + item }}"
   register: "matrix_synapse_workers_list_results_media_repository_workers"
@@ -62,6 +100,8 @@
     {{
       matrix_synapse_workers_list_results_generic_workers.results
       +
+      matrix_synapse_workers_list_results_stream_writer_workers.results
+      +
       matrix_synapse_workers_list_results_federation_sender_workers.results
       +
       matrix_synapse_workers_list_results_pusher_workers.results
diff --git a/roles/matrix-synapse/tasks/synapse/workers/util/inject_systemd_services_for_worker.yml b/roles/matrix-synapse/tasks/synapse/workers/util/inject_systemd_services_for_worker.yml
deleted file mode 100644
index 2ecb3f2b..00000000
--- a/roles/matrix-synapse/tasks/synapse/workers/util/inject_systemd_services_for_worker.yml
+++ /dev/null
@@ -1,19 +0,0 @@
----
-# The tasks below run before `validate_config.yml`.
-# To avoid failing with a cryptic error message, we'll do validation here.
-#
-# This check is mostly relevant to people who explicitly define `matrix_synapse_workers_enabled_list`
-# (Synapse Workers users from the earlier days of this PR - https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/456).
-#
-# In the future, it should be possible to remove this check.
-# Our own code which dynamically builds `matrix_synapse_workers_enabled_list` does things right.
-- name: Fail if instanceId not defined for worker
-  ansible.builtin.fail:
-    msg: "Synapse workers (like {{ matrix_synapse_worker_details | to_json }}) need to define an instanceId property (type + instanceId must be unique)"
-  when: "'instanceId' not in matrix_synapse_worker_details"
-
-- ansible.builtin.set_fact:
-    matrix_synapse_worker_systemd_service_name: "matrix-synapse-worker-{{ matrix_synapse_worker_details.type }}-{{ matrix_synapse_worker_details.instanceId }}.service"
-
-- ansible.builtin.set_fact:
-    matrix_systemd_services_list: "{{ matrix_systemd_services_list + [matrix_synapse_worker_systemd_service_name] }}"
diff --git a/roles/matrix-synapse/tasks/synapse/workers/util/inject_worker.yml b/roles/matrix-synapse/tasks/synapse/workers/util/inject_worker.yml
new file mode 100644
index 00000000..4f6b4398
--- /dev/null
+++ b/roles/matrix-synapse/tasks/synapse/workers/util/inject_worker.yml
@@ -0,0 +1,65 @@
+---
+# The tasks below run before `validate_config.yml`.
+# To avoid failing with a cryptic error message, we'll do validation here.
+#
+# This check is mostly relevant to people who explicitly define `matrix_synapse_workers_enabled_list`
+# (Synapse Workers users from the earlier days of this PR - https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/456).
+#
+# In the future, it should be possible to remove this check.
+# Our own code which dynamically builds `matrix_synapse_workers_enabled_list` does things right.
+- name: Fail if required property not defined for worker
+  ansible.builtin.fail:
+    msg: "Synapse workers (like {{ matrix_synapse_worker_details | to_json }}) need to define a `{{ item }}` property"
+  with_items:
+    - id
+    - name
+    - type
+    - app
+    - port
+    - webserving
+  when: "item not in matrix_synapse_worker_details"
+
+# Names are used for container names and systemd services.
+# Routing happens based on container names, so Synapse processes that try to route to workers with underscores in the name will complain. Example:
+# > InvalidCodepoint Codepoint U+005F at position 46 of 'matrix-synapse-worker-stream-writer-3-account_data' not allowed
+- name: Fail if worker name includes underscore
+  ansible.builtin.fail:
+    msg: "Unrecognized Synapse worker `name`: `{{ matrix_synapse_worker_details.name }}`. It must not include underscores"
+  when: "'_' in matrix_synapse_worker_details.name"
+
+- name: Fail if worker type unknown
+  ansible.builtin.fail:
+    msg: "Unrecognized Synapse worker `type`: `{{ matrix_synapse_worker_details.type }}`. Supported types are: {{ matrix_synapse_known_worker_types | join(', ') }}"
+  when: "matrix_synapse_worker_details.type not in matrix_synapse_known_worker_types"
+
+- name: Fail if worker app unknown
+  ansible.builtin.fail:
+    msg: "Unrecognized Synapse worker `app`: `{{ matrix_synapse_worker_details.app }}`. Supported types are: {{ matrix_synapse_workers_avail_list | join(', ') }}"
+  when: "matrix_synapse_worker_details.app not in matrix_synapse_workers_avail_list"
+
+- block:
+    - name: Fail if stream_writer_stream not defined for stream_writer worker
+      ansible.builtin.fail:
+        msg: >-
+          Synapse stream_writer workers (such as {{ item }}) need to define a valid `stream_writer_stream` property
+          (not `{{ matrix_synapse_worker_details.stream_writer_stream|default('undefined') }}`).
+          Supported types are: {{ matrix_synapse_workers_known_stream_writer_stream_types | join(', ') }}
+      when: "'stream_writer_stream' not in matrix_synapse_worker_details or matrix_synapse_worker_details.stream_writer_stream not in matrix_synapse_workers_known_stream_writer_stream_types"
+
+    - name: Fail if replication_port not defined for stream_writer worker
+      ansible.builtin.fail:
+        msg: "Synapse background workers of type stream_writer (such as {{ item }}) need to define a valid `replication_port` property"
+      when: "'replication_port' not in matrix_synapse_worker_details"
+  when: "matrix_synapse_worker_details.type == 'stream_writer'"
+
+- ansible.builtin.set_fact:
+    matrix_systemd_services_list: "{{ matrix_systemd_services_list + [matrix_synapse_worker_details.name + '.service'] }}"
+
+- ansible.builtin.set_fact:
+    matrix_synapse_webserving_workers_systemd_services_list: "{{ matrix_synapse_webserving_workers_systemd_services_list + [matrix_synapse_worker_details.name + '.service'] }}"
+  when: matrix_synapse_worker_details.webserving | bool
+
+# Inject stream writers and various other background workers into the instance map.
+- ansible.builtin.set_fact:
+    matrix_synapse_instance_map: "{{ matrix_synapse_instance_map | combine({matrix_synapse_worker_details.name: {'host': matrix_synapse_worker_details.name, 'port': matrix_synapse_worker_details.replication_port}}) }}"
+  when: matrix_synapse_worker_details.type in matrix_synapse_known_instance_map_eligible_worker_types
diff --git a/roles/matrix-synapse/tasks/synapse/workers/util/setup_files_for_worker.yml b/roles/matrix-synapse/tasks/synapse/workers/util/setup_files_for_worker.yml
index d6d4924f..d3f30917 100644
--- a/roles/matrix-synapse/tasks/synapse/workers/util/setup_files_for_worker.yml
+++ b/roles/matrix-synapse/tasks/synapse/workers/util/setup_files_for_worker.yml
@@ -1,13 +1,9 @@
 ---
 
 - ansible.builtin.set_fact:
-    matrix_synapse_worker_systemd_service_name: "matrix-synapse-worker-{{ matrix_synapse_worker_details.type }}-{{ matrix_synapse_worker_details.instanceId }}"
-
-- ansible.builtin.set_fact:
-    matrix_synapse_worker_container_name: "{{ matrix_synapse_worker_systemd_service_name }}"
-
-- ansible.builtin.set_fact:
-    matrix_synapse_worker_config_file_name: "worker.{{ matrix_synapse_worker_details.type }}_{{ matrix_synapse_worker_details.instanceId }}.yaml"
+    matrix_synapse_worker_systemd_service_name: "{{ matrix_synapse_worker_details.name }}"
+    matrix_synapse_worker_container_name: "{{ matrix_synapse_worker_details.name }}"
+    matrix_synapse_worker_config_file_name: "worker.{{ matrix_synapse_worker_details.name }}.yaml"
 
 - name: Ensure configuration exists for {{ matrix_synapse_worker_systemd_service_name }}
   ansible.builtin.template:
diff --git a/roles/matrix-synapse/tasks/validate_config.yml b/roles/matrix-synapse/tasks/validate_config.yml
index bcb71c75..1fc70816 100644
--- a/roles/matrix-synapse/tasks/validate_config.yml
+++ b/roles/matrix-synapse/tasks/validate_config.yml
@@ -32,6 +32,11 @@
   with_items:
     - "matrix_synapse_workers_pusher_workers_count"
     - "matrix_synapse_workers_federation_sender_workers_count"
+    - "matrix_synapse_workers_stream_writer_typing_stream_workers_count"
+    - "matrix_synapse_workers_stream_writer_to_device_stream_workers_count"
+    - "matrix_synapse_workers_stream_writer_account_data_stream_workers_count"
+    - "matrix_synapse_workers_stream_writer_receipts_stream_workers_count"
+    - "matrix_synapse_workers_stream_writer_presence_stream_workers_count"
 
 - name: (Deprecation) Catch and report renamed settings
   ansible.builtin.fail:
diff --git a/roles/matrix-synapse/templates/synapse/homeserver.yaml.j2 b/roles/matrix-synapse/templates/synapse/homeserver.yaml.j2
index 04c4b3cf..86d03be4 100644
--- a/roles/matrix-synapse/templates/synapse/homeserver.yaml.j2
+++ b/roles/matrix-synapse/templates/synapse/homeserver.yaml.j2
@@ -352,13 +352,13 @@ worker_app: synapse.app.homeserver
 
 # thx https://oznetnerd.com/2017/04/18/jinja2-selectattr-filter/
 # reduce the main worker's offerings to core homeserver business
-{% if matrix_synapse_workers_enabled_list | selectattr('type', 'equalto', 'federation_sender') | list  %}
+{% if matrix_synapse_workers_enabled_list | selectattr('type', 'equalto', 'federation_sender') | list | length > 0  %}
 send_federation: false
 {% endif %}
-{% if matrix_synapse_workers_enabled_list | selectattr('type', 'equalto', 'media_repository') | list  %}
+{% if matrix_synapse_workers_enabled_list | selectattr('type', 'equalto', 'media_repository') | list | length > 0  %}
 enable_media_repo: false
 {% endif %}
-{% if matrix_synapse_workers_enabled_list | selectattr('type', 'equalto', 'pusher') | list  %}
+{% if matrix_synapse_workers_enabled_list | selectattr('type', 'equalto', 'pusher') | list | length > 0  %}
 start_pushers: false
 {% endif %}
 
@@ -2870,6 +2870,7 @@ opentracing:
 #  worker1:
 #    host: localhost
 #    port: 8034
+instance_map: {{ matrix_synapse_instance_map | to_json }}
 
 # Experimental: When using workers you can define which workers should
 # handle event persistence and typing notifications. Any worker
@@ -2878,6 +2879,7 @@ opentracing:
 #stream_writers:
 #  events: worker1
 #  typing: worker1
+stream_writers: {{ matrix_synapse_stream_writers | to_json }}
 
 # The worker that is used to run background tasks (e.g. cleaning up expired
 # data). If not provided this defaults to the main process.
diff --git a/roles/matrix-synapse/templates/synapse/prometheus/external_prometheus.yml.example.j2 b/roles/matrix-synapse/templates/synapse/prometheus/external_prometheus.yml.example.j2
index b194c3c2..1501697d 100644
--- a/roles/matrix-synapse/templates/synapse/prometheus/external_prometheus.yml.example.j2
+++ b/roles/matrix-synapse/templates/synapse/prometheus/external_prometheus.yml.example.j2
@@ -24,8 +24,8 @@ scrape_configs:
           job: "master"
           index: "0"
 {% for worker in matrix_synapse_workers_enabled_list %}
-  - job_name: 'synapse-{{ worker.type }}-{{ worker.instanceId }}'
-    metrics_path: /metrics/synapse/worker/{{ worker.type }}-{{ worker.instanceId }}
+  - job_name: '{{ worker.name }}'
+    metrics_path: /metrics/synapse/worker/{{ worker.id }}
     scheme: {{ 'https' if matrix_nginx_proxy_https_enabled|default(true) else 'http' }}
 {% if matrix_nginx_proxy_proxy_matrix_metrics_basic_auth_enabled|default(true) %}
     basic_auth:
@@ -35,6 +35,7 @@ scrape_configs:
     static_configs:
       - targets: ['{{ matrix_server_fqn_matrix }}:{{ matrix_nginx_proxy_container_https_host_bind_port|default(443) if matrix_nginx_proxy_https_enabled|default(true) else matrix_nginx_proxy_container_http_host_bind_port|default(80) }}']
         labels:
+          worker_id: {{ worker.id }}
           job: "{{ worker.type }}"
-          index: "{{ worker.instanceId }}"
+          app: {{ worker.app }}
 {% endfor %}
diff --git a/roles/matrix-synapse/templates/synapse/systemd/matrix-synapse-worker.service.j2 b/roles/matrix-synapse/templates/synapse/systemd/matrix-synapse-worker.service.j2
index 4a38251d..96b65a0a 100644
--- a/roles/matrix-synapse/templates/synapse/systemd/matrix-synapse-worker.service.j2
+++ b/roles/matrix-synapse/templates/synapse/systemd/matrix-synapse-worker.service.j2
@@ -43,7 +43,7 @@ ExecStart={{ matrix_host_command_docker }} run --rm --name {{ matrix_synapse_wor
 			{{ arg }} \
 			{% endfor %}
 			{{ matrix_synapse_docker_image }} \
-			run -m synapse.app.{{ matrix_synapse_worker_details.type }} -c /data/homeserver.yaml -c /data/{{ matrix_synapse_worker_config_file_name }}
+			run -m synapse.app.{{ matrix_synapse_worker_details.app }} -c /data/homeserver.yaml -c /data/{{ matrix_synapse_worker_config_file_name }}
 
 
 ExecStop=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} kill {{ matrix_synapse_worker_container_name }} 2>/dev/null || true'
diff --git a/roles/matrix-synapse/templates/synapse/systemd/matrix-synapse.service.j2 b/roles/matrix-synapse/templates/synapse/systemd/matrix-synapse.service.j2
index 027114fb..eed50ad1 100644
--- a/roles/matrix-synapse/templates/synapse/systemd/matrix-synapse.service.j2
+++ b/roles/matrix-synapse/templates/synapse/systemd/matrix-synapse.service.j2
@@ -12,7 +12,7 @@ Wants={{ service }}
 
 {% if matrix_synapse_workers_enabled %}
 {% for matrix_synapse_worker_details in matrix_synapse_workers_enabled_list %}
-Wants=matrix-synapse-worker-{{ matrix_synapse_worker_details.type }}-{{ matrix_synapse_worker_details.port }}.service
+Wants={{ matrix_synapse_worker_details.name }}.service
 {% endfor %}
 {% endif %}
 
diff --git a/roles/matrix-synapse/templates/synapse/worker.yaml.j2 b/roles/matrix-synapse/templates/synapse/worker.yaml.j2
index 33789b0c..c9637a83 100644
--- a/roles/matrix-synapse/templates/synapse/worker.yaml.j2
+++ b/roles/matrix-synapse/templates/synapse/worker.yaml.j2
@@ -1,27 +1,38 @@
 #jinja2: lstrip_blocks: "True"
-worker_app: synapse.app.{{ matrix_synapse_worker_details.type }}
-worker_name: {{ matrix_synapse_worker_details.type ~ ':' ~ matrix_synapse_worker_details.port }}
+worker_app: synapse.app.{{ matrix_synapse_worker_details.app }}
+worker_name: {{ matrix_synapse_worker_details.name }}
 
 {% if matrix_synapse_replication_listener_enabled %}
 worker_replication_host: matrix-synapse
 worker_replication_http_port: {{ matrix_synapse_replication_http_port }}
 {% endif %}
 
-{% set has_listeners = (matrix_synapse_worker_details.type not in [ 'appservice', 'federation_sender', 'pusher' ] or matrix_synapse_metrics_enabled) %}
-
 {% set http_resources = [] %}
 
-{% if matrix_synapse_worker_details.type in ['generic_worker', 'user_dir'] %}
+{% if matrix_synapse_worker_details.type == 'user_dir' %}
   {% set http_resources = http_resources + ['client'] %}
 {% endif %}
-{% if matrix_synapse_worker_details.type in ['generic_worker'] %}
-  {% set http_resources = http_resources+ ['federation'] %}
+{% if matrix_synapse_worker_details.type == 'generic_worker' %}
+  {% set http_resources = http_resources + ['client', 'federation'] %}
 {% endif %}
-{% if matrix_synapse_worker_details.type in ['media_repository'] %}
+{#
+  None of the background workers need to handle federation traffic.
+  Only some of the stream writers need to handle client traffic.
+#}
+{% if matrix_synapse_worker_details.type == 'stream_writer' and matrix_synapse_worker_details.webserving %}
+  {% set http_resources = http_resources + ['client'] %}
+{% endif %}
+{% if matrix_synapse_worker_details.type == 'media_repository' %}
   {% set http_resources = http_resources + ['media'] %}
 {% endif %}
 
-{% if http_resources|length > 0 or matrix_synapse_metrics_enabled %}
+{% set replication_http_resources = [] %}
+{% if matrix_synapse_worker_details.type == 'stream_writer' %}
+  {# All background workers need to handle replication traffic. #}
+  {% set replication_http_resources = replication_http_resources + ['replication'] %}
+{% endif %}
+
+{% if http_resources|length > 0 or matrix_synapse_metrics_enabled or replication_http_resources|length > 0 %}
 worker_listeners:
 {% if http_resources|length > 0 %}
   - type: http
@@ -36,6 +47,13 @@ worker_listeners:
     bind_addresses: ['0.0.0.0']
     port: {{ matrix_synapse_worker_details.metrics_port }}
 {% endif %}
+{% if replication_http_resources|length > 0 %}
+  - type: http
+    bind_addresses: ['::']
+    port: {{ matrix_synapse_worker_details.replication_port }}
+    resources:
+      - names: {{ replication_http_resources|to_json }}
+{% endif %}
 {% endif %}
 
 {% if matrix_synapse_worker_details.type == 'generic_worker' %}
diff --git a/roles/matrix-synapse/vars/main.yml b/roles/matrix-synapse/vars/main.yml
index 2d9b62cf..e8b0e49c 100644
--- a/roles/matrix-synapse/vars/main.yml
+++ b/roles/matrix-synapse/vars/main.yml
@@ -36,3 +36,58 @@ matrix_synapse_workers_generic_worker_federation_endpoints: "{{ matrix_synapse_w
 # matrix_synapse_workers_generic_worker_federation_endpoints_regex contains the regex used in matrix_synapse_workers_generic_worker_federation_endpoints.
 # It's intentionally put in a separate variable, to avoid tripping ansible-lint's var-spacing rule.
 matrix_synapse_workers_generic_worker_federation_endpoints_regex: '.*(/_matrix/federation|/_matrix/key).*'
+
+# matrix_synapse_workers_stream_writer_typing_stream_worker_client_server_endpoints contains the endpoints serviced by the `typing` stream writer.
+# See: https://matrix-org.github.io/synapse/latest/workers.html#the-typing-stream
+matrix_synapse_workers_stream_writer_typing_stream_worker_client_server_endpoints:
+  - ^/_matrix/client/(api/v1|r0|v3|unstable)/rooms/.*/typing
+
+# matrix_synapse_workers_stream_writer_to_device_stream_worker_client_server_endpoints contains the endpoints serviced by the `to_device` stream writer.
+# See: https://matrix-org.github.io/synapse/latest/workers.html#the-to_device-stream
+matrix_synapse_workers_stream_writer_to_device_stream_worker_client_server_endpoints:
+  - ^/_matrix/client/(r0|v3|unstable)/sendToDevice/
+
+# matrix_synapse_workers_stream_writer_account_data_stream_worker_client_server_endpoints contains the endpoints serviced by the `account_data` stream writer.
+# See: https://matrix-org.github.io/synapse/latest/workers.html#the-account_data-stream
+matrix_synapse_workers_stream_writer_account_data_stream_worker_client_server_endpoints:
+  - ^/_matrix/client/(r0|v3|unstable)/.*/tags
+  - ^/_matrix/client/(r0|v3|unstable)/.*/account_data
+
+# matrix_synapse_workers_stream_writer_receipts_stream_worker_client_server_endpoints contains the endpoints serviced by the `recepts` stream writer.
+# See: https://matrix-org.github.io/synapse/latest/workers.html#the-receipts-stream
+matrix_synapse_workers_stream_writer_receipts_stream_worker_client_server_endpoints:
+  - ^/_matrix/client/(r0|v3|unstable)/rooms/.*/receipt
+  - ^/_matrix/client/(r0|v3|unstable)/rooms/.*/read_markers
+
+# matrix_synapse_workers_stream_writer_presence_stream_worker_client_server_endpoints contains the endpoints serviced by the `presence` stream writer.
+# See: https://matrix-org.github.io/synapse/latest/workers.html#the-presence-stream
+matrix_synapse_workers_stream_writer_presence_stream_worker_client_server_endpoints:
+  - ^/_matrix/client/(api/v1|r0|v3|unstable)/presence/
+
+# matrix_synapse_workers_known_stream_writer_stream_types contains the list of stream writer stream types that the playbook recognizes.
+# This is used for validation purposes. If adding support for a new type, besides adding it to this list,
+# don't forget to actually configure it where appropriate (see worker.yaml.j2`, the nginx proxy configuration, etc).
+matrix_synapse_workers_known_stream_writer_stream_types: ['events', 'typing', 'to_device', 'account_data', 'receipts', 'presence']
+
+# matrix_synapse_workers_webserving_stream_writer_types contains a list of stream writer types that serve web (client) requests.
+# Not all stream writers serve web requests. Some just perform background tasks.
+matrix_synapse_workers_webserving_stream_writer_types: ['typing', 'to_device', 'account_data', 'receipts', 'presence']
+
+# matrix_synapse_workers_systemd_services_list contains a list of systemd services (one for each worker systemd service which serves web requests).
+# This list is built during runtime.
+# Not all workers serve web requests. Those that don't won't be injected here.
+matrix_synapse_webserving_workers_systemd_services_list: []
+
+# matrix_synapse_known_worker_types contains the list of known worker types.
+# A worker type is different than a worker app (e.g. `generic_worker`).
+# For example, the `stream_writer` worker type is served by the `generic_worker` app, but is a separate type that we recognize.
+matrix_synapse_known_worker_types: |
+  {{
+    matrix_synapse_workers_avail_list
+    +
+    ['stream_writer']
+  }}
+
+# matrix_synapse_known_instance_map_eligible_worker_types contains the list of worker types that are to be injected into `matrix_synapse_instance_map`.
+matrix_synapse_known_instance_map_eligible_worker_types:
+  - stream_writer