Restrict NodeExporter to listen only on localhost by default
Description
Since Omnibus packages Prometheus and its collected exporters and runs them on the same host, we can leverage this to reduce the number of ports available externally.
Proposal
We should:
- By default have NodeExporter only listen on
localhost:9100
- Expose an option in gitlab.rb to override the listen address.
I believe NodeExporter offers a CLI argument (-web.listen-address) to allow us to configure this.