Add `proxy-url` command line option

[kriswuollett]

What would you like to be added:

Add proxy-url command line option to override cluster setting in selected context config.

Why is this needed:

Golang doesn't support HTTPS_PROXY for localhost addresses as noted in #1653. Avoids the need to statically set proxy urls for each of the clusters defined in a config file.

[xyz-li]

/assign

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/lifecycle stale

[k8s-triage-robot]

The Kubernetes project currently lacks enough active contributors to adequately respond to all issues.

This bot triages un-triaged issues according to the following rules:

• After 90d of inactivity, lifecycle/stale is applied
• After 30d of inactivity since lifecycle/stale was applied, lifecycle/rotten is applied
• After 30d of inactivity since lifecycle/rotten was applied, the issue is closed

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/lifecycle rotten

[ardaguclu]

I think you can use kubectl proxy command for this case or modify your host file from localhost to something else. Because Go probably checks the equality of localhost and using something different will enable HTTPS_PROXY env var.

I think, we'd not prefer adding flag for this;

/close

[k8s-ci-robot]

@ardaguclu: Closing this issue.

In response to this:

I think you can use kubectl proxy command for this case or modify your host file from localhost to something else. Because Go probably checks the equality of localhost and using something different will enable HTTPS_PROXY env var.

I think, we'd not prefer adding flag for this;

/close

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[BenTheElder]

I think you can use kubectl proxy command for this case or modify your host file from localhost to something else. Because Go probably checks the equality of localhost and using something different will enable HTTPS_PROXY env var.

editing /etc/hosts is not portable / generally painful

go specifically checks for localhost hostname or loopback IP addresses previously reported in https://github.com/kubernetes/kubectl/issues/743 https://cs.opensource.google/go/x/net/+/refs/tags/v0.39.0:http/httpproxy/proxy.go;l=178-185

this only happens if you use FromEnvironment() proxy config, which we don't use in the code path where proxy-url is set in kubeconfig

if you set proxy-url in your kubeconfig, then we bypass the go stdlib behavior to ignore proxy for localhost (https://github.com/kubernetes-sigs/kind/issues/3900#issuecomment-2757706919)

it makes sense that the env would continue to use FromEnvironment, but a flag could be treated like setting it in the kubeconfig

this turns out to be annoying for testing kubectl, because kind clusters are on localhost ... https://github.com/kubernetes-sigs/kind/issues/3900

(especially because when testing there may not be a kubeconfig, there may only be --server and related flags, but there is no equivalent for the proxy-url config option)

cc @kubernetes/sig-cli-leads can we reconsider allowing --proxy-url to behave like proxy-url in config in the way that --server does?

I think this is a recurring problem for testing with proxies, some examples:

https://github.com/kubernetes/kubectl/issues/1653 https://github.com/kubernetes/kubectl/issues/743 https://github.com/kubernetes-sigs/kind/issues/3900

[ardaguclu]

Makes sense. Let's reopen this and continue discussions /reopen

[k8s-ci-robot]

@ardaguclu: Reopened this issue.

In response to this:

Makes sense. Let's reopen this and continue discussions /reopen

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[soltysh]

cc @kubernetes/sig-cli-leads can we reconsider allowing --proxy-url to behave like proxy-url in config in the way that --server does?

We don't have a --proxy-url flag exposed anywhere, but it seems like a reasonable addition.

[mpuckett159]

/triage accepted

[DevanOBoyle]

I'd like to take a crack at this

[rushmash91]

Hi @DevanOBoyle, Are you still working on this?

I've implemented the --proxy-url flag discussed here. The implementation adds the flag to ConfigFlags and treats it like setting proxy-url in kubeconfig, which bypasses Go's FromEnvironment() limitation for localhost addresses.

@ardaguclu @soltysh @mpuckett159 Here's the small PR for review and further discussions: https://github.com/kubernetes/kubernetes/pull/133069 /assign