prometheus-adapter: allow to set custom prometheus URL path

[xaurx]

There is no way to specify prometheus listening on non-root endpoint to prometheus-adapter.
e.g. http://prometheus-svc:9090/prometheus.

There are solutions possible:

• check if port == 0 and omit ":port" from URL at all
• add new value param

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• DCO signed
• Chart Version bumped
• Variables are documented in the README.md

[k8s-ci-robot]

Hi @xaurx. Thanks for your PR.

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[davidkarlsen]

shouldn't this be /prometheus by default?

[xaurx]

@davidkarlsen By default prometheus serves / URI (root). There is an option to add some prefix for Prometheus URIs and make it serve /prefix/. This is used in environments where you want to share same hostname for multiple services and route HTTP requests based on URI path via API gateway.

[steven-sheehy]

As a user of the chart, I think it's pretty silly that you have to specify components of a URL (port and path) in addition to the prometheus.url. It should just be prometheus.url and it should include the port and path as URLs usually do. This would be a non-backwards compatible change, though.

[xaurx]

As a user of the chart, I think it's pretty silly that you have to specify components of a URL (port and path) in addition to the prometheus.url. It should just be prometheus.url and it should include the port and path as URLs usually do. This would be a non-backwards compatible change, though.

@steven-sheehy Yes, I found it silly as well, but quickly realised PR won't be accepted if breaks current users. Another option is to check if port is zero, then we can omit ":" before the port and substitute URL only.
I think it should look like this than:
- --prometheus-url={{ .Values.prometheus.url }}{{ if ne .Values.prometheus.port 0 }}:{{ .Values.prometheus.port }}{{end}}
If this is ok to everybody, I can rework this way...

[xaurx]

/assign @lachie83

[steven-sheehy]

/approve
/ok-to-test

[steven-sheehy]

Please bump chart version

[xaurx]

Please bump chart version

@steven-sheehy done

[xaurx]

@steven-sheehy anything else to do?

[steven-sheehy]

@xaurx It LGTM, but we need someone with commit rights to lgtm it.

@davidkarlsen or @mattfarina Mind reviewing?

[mattfarina]

cc @MattiasGees

[mattfarina]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mattfarina, steven-sheehy, xaurx

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