matrix-docker-ansible-deploy/docs/configuring-playbook-external-postgres.md

Using an external PostgreSQL server (optional)

By default, this playbook would set up a PostgreSQL database server on your machine, running in a Docker container. If that's alright, you can skip this.

If you'd like to use an external PostgreSQL server that you manage, you can edit your configuration file (inventory/matrix.<your-domain>/vars.yml). It should be something like this:

matrix_postgres_enabled: false

# Rewire Synapse to use your external Postgres server
matrix_synapse_database_host: "your-postgres-server-hostname"
matrix_synapse_database_user: "your-postgres-server-username"
matrix_synapse_database_password: "your-postgres-server-password"
matrix_synapse_database_database: "your-postgres-server-database-name"

The database (as specified in matrix_synapse_database_database) must exist and be accessible with the given credentials. It must be empty or contain a valid Synapse database. If empty, Synapse would populate it the first time it runs.

Note: the external server that you specify in matrix_synapse_database_host must be accessible from within the matrix-synapse Docker container (and possibly other containers too). This means that it either needs to be a publicly accessible hostname or that it's a hostname on the same Docker network where all containers installed by this playbook run (a network called matrix by default). Using a local PostgreSQL instance on the host (running on the same machine, but not in a container) is not possible.