Enabling prometheus-exporter plugin with Discourse Docker instance

Installation
1

Hello,

I have an instance of Discourse running in a Docker container with the prometheus-exporter installed. We are using bundle exec rails server -b 0.0.0.0 to start the rails server (using /bin/unicorn/ gives the same error) and have specified the port mapping 9045:9045 and exposed port 9045.

The puma error logs show the following errors:

Prometheus Exporter, failed to send message Cannot assign requested address - connect(2) for "localhost" port 9405

2022-08-09 22:48:25 +0000 Rack app ("GET /metrics" - (172.22.0.1)): #<Errno::EADDRNOTAVAIL: Failed to open TCP connection to localhost:9405 (Cannot assign requested address - connect(2) for "localhost" port 9405)>

Is there something special Discourse normally does with puma to ensure that the prometheus-exporter can open a TCP connection on port 9405?

2

If you install Discourse following the official install guide it won’t use Puma, but Unicorn. All our plugins and themes assume an install that follows the official install.