Add some Prometheus metrics:

[tomwilkie]

Change Description

Add some Prometheus metrics:

• cloudsql_proxy_active_connections
• cloudsql_proxy_max_connections
• cloudsql_proxy_connections_total
• cloudsql_proxy_connections_errors_total

Checklist

• Make sure to open an issue as a
  bug/issue
  before writing your code! That way we can discuss the change, evaluate
  designs, and agree on the general idea.
• Ensure the tests and linter pass
• Appropriate documentation is updated (if necessary)

Relevant issues:

• Fixes Add support for metrics / tracing #169

[kurtisvg]

2 quick high level thoughts:

1. I'd much rather target Opencensus and be able to support both Prometheus and Stackdriver metrics
2. We probably (at least initially) mark the flag as experimental - particularly because I would ideally like to be able to provide more instance specific connections, and don't want to have to do a major version bump if that effects the metric surface.

[Carrotman42]

Just so that we are clear about what the impact of adding this dependency is, do you mind reporting the before/after size of the binary?

[tomwilkie]

I'd much rather target Opencensus and be able to support both Prometheus and Stackdriver metrics

I thought Opencensus was deprecated and Opentelemetry wasn't ready yet... Either way not super familiar with either. I think there are plenty of ways to get Prometheus metrics into stackdriver.

We probably (at least initially) mark the flag as experimental - particularly because I would ideally like to be able to provide more instance specific connections, and don't want to have to do a major version bump if that effects the metric surface.

Done!

Just so that we are clear about what the impact of adding this dependency is, do you mind reporting the before/after size of the binary?

twilkie@MacBook-Pro cloudsql-proxy % git checkout  master 
twilkie@MacBook-Pro cloudsql-proxy % GOOS=linux go build ./cmd/cloud_sql_proxy
twilkie@MacBook-Pro cloudsql-proxy % ls -l cloud_sql_proxy                   
-rwxr-xr-x  1 twilkie  staff  16391258 15 Oct 09:50 cloud_sql_proxy

twilkie@MacBook-Pro cloudsql-proxy % git checkout  prometheus 
Switched to branch 'prometheus'
twilkie@MacBook-Pro cloudsql-proxy % GOOS=linux go build ./cmd/cloud_sql_proxy
twilkie@MacBook-Pro cloudsql-proxy % ls -l cloud_sql_proxy                    
-rwxr-xr-x  1 twilkie  staff  17930396 15 Oct 09:51 cloud_sql_proxy

[kurtisvg]

I thought Opencensus was deprecated and Opentelemetry wasn't ready yet... Either way not super familiar with either. I think there are plenty of ways to get Prometheus metrics into stackdriver.

OpenCensus isn't deprecated, but most of the feature work is focused on OpenTelemetry. OpenTelemetry is currently in Beta and is supposed to GA sometime before the end of the year.

You can export Prometheus metrics to Stackdriver, but requires you to collect them in a prometheus server and export them. Using OpenCensus means we could provide users an option to specify an exporter to either Prometheus or Stackdriver (or one of the other supported exporters).

[withnale]

Is this PR dead now? It was going to provide really useful visibility

[enocom]

As mentioned in #600, we're working on some major structural improvements in addition to waiting for OpenTelemetry to go GA. Once those are done, we're going to circle back and add first-class support for metrics and tracing to the proxy. For now, I'd like to leave this PR open for reference in case others need Prometheus support with the caveat that we're not going to merge it.

[enocom]

As of #1215, we have support for Prometheus metrics in the v2 branch. We're working on a migration guide and making v2 the main branch, but until then I'm going to close this.