build: add example on how to use proxy with GHA

[dvdksn]

Signed-off-by: David Karlsson david.karlsson@docker.com

Proposed changes

Adds an example on how to set up a proxy with Docker GitHub Actions

Related issues (optional)

docker/build-push-action#822

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[crazy-max]

Thanks!

I wonder if we also need a page in "Building images" with a proxy page because we also need to explain that the proxy configuration from the Docker config is used if detected (see https://github.com/crazy-max/docker-build-push-action/blob/6509d7e99a330cd52fb169549758512aa83ca878/.github/workflows/ci.yml#L1021-L1040).

We also need to explain how to set proxy build args when doing a build instead of global daemon set: https://docs.docker.com/engine/reference/builder/#predefined-args. This will only work for RUN instructions and not for pulling imaging or fetching git repos. For this case it needs to be set in buildkit as env driver opt.

Let me know what sounds best

[dvdksn]

@crazy-max proxy configurations are described on this page, it includes information about config.json. It also describes how these settings are used for building, and using build-arg

[tonistiigi]

Not blocking this but it might be somewhat confusing to new readers why anyone would like to do this.

If we talk about just setting environment variables to buildkit containers then this could be in configure-builder where it is showing some other driver-opts like setting image.

For configuring a proxy for builds we usually mean either passing proxy env as with --build-arg or configuring the proxy setting in Docker CLI conf where buildx reads them.

[docker-robot]

Thanks for the pull request. We'd like to make our product docs better, but haven’t been able to review all the suggestions.
As our docs have also diverged, we do not have the bandwidth to review and rebase old pull requests.

If the updates are still relevant, review our contribution guidelines and rebase your pull request against the latest version of the docs, then mark it as fresh with a /remove-lifecycle stale comment.
If not, this pull request will be closed in 30 days. This helps our maintainers focus on the active pull requests.

Prevent pull requests from auto-closing with a /lifecycle frozen comment.

/lifecycle stale