Registry mirror

[AurelienGasser]

Registry mirrors allow base images to be pulled from an arbitrary Docker registry instead of the default index.docker.io.

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A similar feature exists in kaniko.

Registry mirrors are useful in various scenarios, including cases when internet connectivity is not available (e.g. VPC without internet gateway), and Dockerfiles cannot easily be modified.

We'd love to use makisu instead of kaniko (makisu is faster in our use-case!) but the lack of support for registry mirrors is a blocker.