Home Assistant uses PostgreSQL for recording the history of entity
states. Since we had been using the in-cluster database server for
this, the data were migrated to the new external PostgreSQL server
automatically when the backup from the former was restored on the
latter. It follows, then, that we can point Home Assistant to the
new server as well.
Home Assistant uses SQLAlchemy, which in turn uses _libpq_ via
_psycopg_, as a client for PostgreSQL. It doesn't expose any
configuration parameters beyond the "database URL" directly, but we
can use the standard environment variables to specify the certificate
and private key for authentication. In fact, the empty `postgresql://`
URL is sufficient, and indicates that _all_ of the connection parameters
should be taken from environment variables. This makes specifying the
parameters for both the `wait-for-db` init container and the main
container take the exact same environment variables, so we can use
YAML anchors to share their definitions.
Dustin