Feature request: Expose HTTP request metrics

[juliusv]

As far as I can see, kamal-proxy does not yet expose metrics about the requests it serves. It would be really nice if it tracked e.g. Prometheus metrics for things like:

• Request counts (including status code label dimension)
• Request duration histogram
• Request size histogram
• Response size histogram
• Current number of in-flight requests
• Etc.

[northeastprince]

Request metrics seen more like a responsibility for the apps themselves.

[juliusv]

That's ok, though it's pretty common to have them in both places. Usually apps are instrumented, and proxies / LBs like nginx, HAProxy, etc. also track metrics about requests going to their services and backends.

[gouthamve]

Can I request that this be reopened? Lets say the application is crashing and kamal-proxy is returning 5xx, we cannot alert on this because the app itself is down and kamal-proxy has no metrics.

Further, there can be cases where the proxy latency is different from app latencies, and the proxy latencies are much closer to what users see. It's best to also expose metrics from the proxy to diagnose this issue.

[polarctos]

Metrics via HTTP are now available, added in: #126 available in v0.9.1

kamal-proxy/internal/cmd/run.go

Line 30 in 950b252

runCommand.cmd.Flags().IntVar(&globalConfig.MetricsPort, "metrics-port", getEnvInt("METRICS_PORT", 0), "Publish metrics on the specified port (default zero to disable)")

You can add e.g. --metrics-port=9001 to enable it.

Whats not there yet is metrics via HTTPS port.

I was wondering about adding an additional flag --metrics-https=true to toggle setting the TLS config on the metrics server too.

[polarctos]

Opened a PR for HTTPS: #161

[kevinmcconnell]

@polarctos thanks for answering this!

I had some questions about the HTTPS option that I'd like to understand better. I've moved that discussion to the PR.