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Configuring the Registry Mirror Extension

Introduction

Use-case

containerd allows registry mirrors to be configured. Use-cases are:

  • Usage of public mirror(s) - for example circumvent issues with the upstream registry such as rate limiting, outages and others.
  • Usage of private mirror(s) - for example reduce network costs by using a private mirror running in the same network.

Solution

The registry-mirror extension allows registry mirror configuration to be configured via the Shoot spec directly.

How does it work?

When the extension is enabled, the containerd daemon on the Shoot cluster Nodes gets configured to use as a mirror the requested mirrors. For example, if for upstream docker.io the mirror https://mirror.gcr.io is configured in the Shoot spec, then containerd gets configured to first pull the image from the mirror (https://mirror.gcr.io in that case). If this image pull operation fails, containerd falls back to the upstream itself (docker.io in that case).

The extension is based on the contract described in containerd Registry Configuration. The corresponding upstream documentation in containerd is Registry Configuration - Introduction.

Shoot Configuration

The Shoot specification has to be adapted to include the registry-mirror extension configuration.

Below is an example of registry-mirror extension configuration as part of the Shoot spec:

apiVersion: core.gardener.cloud/v1beta1
kind: Shoot
metadata:
  name: crazy-botany
  namespace: garden-dev
spec:
  extensions:
  - type: registry-mirror
    providerConfig:
      apiVersion: mirror.extensions.gardener.cloud/v1alpha1
      kind: MirrorConfig
      mirrors:
      - upstream: docker.io
        hosts:
        - host: "https://mirror.gcr.io"
          capabilities: ["pull"]

The providerConfig field is required.

The providerConfig.mirrors field contains information about the registry mirrors to configure. It is a required field. At least one mirror has to be specified.

The providerConfig.mirror[].upstream field is the remote registry host to mirror. It is a required field. The value must be a valid DNS subdomain (RFC 1123). It must not include a scheme or port.

The providerConfig.mirror[].hosts field represents the mirror hosts to be used for the upstream. At least one mirror host has to be specified.

The providerConfig.mirror[].hosts.host field is the mirror host. It is a required field. The value must include a scheme - http:// or https://.

The providerConfig.mirror[].hosts.capabilities field represents the operations a host is capable of performing. This also represents the set of operations for which the mirror host may be trusted to perform. Defaults to ["pull"]. The supported values are pull and resolve. See the capabilities field documentation for more information which operations are considered trusted ones against public/private mirrors.