postgres_exporter DSN is not separately configurable, in conflict with the docs
The docs indicate that
postgres_exporter['host'] and password are configurable to a different value than
db_password, but this is not the case: https://gitlab.com/gitlab-org/omnibus-gitlab/blob/master/files/gitlab-cookbooks/monitoring/recipes/postgres-exporter.rb#L26-28.
I've tested this out on an omnibus install and the
postgres_exporter variables indeed have no effect.
My use case is running a single-node geo installation, for which
gitlab_rails['db_host'] must be set to an IP address (even if loopback), and not a socket path in order for the foreign data wrapper to authenticate itself properly (https://staging.gitlab.com/help/administration/geo/replication/troubleshooting.md#fixing-foreign-data-wrapper-errors).
This breaks the postgres_exporter's ability to collect metrics, and to fix it I need to either override the host to the socket path (via which it can access postgres without a password), or to configure a password. Neither of these are possible at the moment.
I'm happy to try to MR this, but figured I'd raise the issue anyway as I've not actually submitted an MR to omnibus before and eyeballs on issues are always good.