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_use_external: true
matrix_postgres_connection_hostname: "your-postgres-server-hostname"
matrix_postgres_connection_username: "your-postgres-server-username"
matrix_postgres_connection_password: "your-postgres-server-password"
matrix_postgres_db_name: "your-postgres-server-database-name"

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