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Image Vector

The Gardenlet is deploying several different container images into the seed and the shoot clusters. The image repositories and tags are defined in a central image vector file. Obviously, the image versions defined there must fit together with the deployment manifests (e.g., some command-line flags do only exist in certain versions).

Example

images:
- name: pause-container
  sourceRepository: github.com/kubernetes/kubernetes/blob/master/build/pause/Dockerfile
  repository: registry.k8s.io/pause
  tag: "3.4"
  version: "1.20.x"
  architectures:
  - amd64
- name: pause-container
  sourceRepository: github.com/kubernetes/kubernetes/blob/master/build/pause/Dockerfile
  repository: registry.k8s.io/pause
  tag: "3.5"
  version: ">= 1.21"
  architectures:
  - amd64
...

That means that the Gardenlet will use the pause-container with tag 3.4 for all seed/shoot clusters with Kubernetes version 1.20.x, and tag 3.5 for all clusters with Kubernetes >= 1.21.

Image Vector Architecture

images:
- name: pause-container
  sourceRepository: github.com/kubernetes/kubernetes/blob/master/build/pause/Dockerfile
  repository: registry.k8s.io/pause
  tag: "3.5"
  architectures:
  - amd64
- name: pause-container
  sourceRepository: github.com/kubernetes/kubernetes/blob/master/build/pause/Dockerfile
  repository: registry.k8s.io/pause
  tag: "3.5"
  architectures:
  - arm64
- name: pause-container
  sourceRepository: github.com/kubernetes/kubernetes/blob/master/build/pause/Dockerfile
  repository: registry.k8s.io/pause
  tag: "3.5"
  architectures:
  - amd64
  - arm64
...

architectures is an optional field of image. It is a list of strings specifying CPU architecture of machines on which this image can be used. The valid options for the architectures field are as follows:

  • amd64 : This specifies that the image can run only on machines having CPU architecture amd64.
  • arm64 : This specifies that the image can run only on machines having CPU architecture arm64.

If an image doesn't specify any architectures, then by default it is considered to support both amd64 and arm64 architectures.

Overwrite Image Vector

In some environments it is not possible to use these "pre-defined" images that come with a Gardener release. A prominent example for that is Alicloud in China, which does not allow access to Google's GCR. In these cases, you might want to overwrite certain images, e.g., point the pause-container to a different registry.

⚠️ If you specify an image that does not fit to the resource manifest, then the seed/shoot reconciliation might fail.

In order to overwrite the images, you must provide a similar file to gardenlet:

images:
- name: pause-container
  sourceRepository: github.com/kubernetes/kubernetes/blob/master/build/pause/Dockerfile
  repository: my-custom-image-registry/pause
  tag: "3.4"
  version: "1.20.x"
- name: pause-container
  sourceRepository: github.com/kubernetes/kubernetes/blob/master/build/pause/Dockerfile
  repository: my-custom-image-registry/pause
  tag: "3.5"
  version: ">= 1.21"
...

During deployment of the gardenlet, create a ConfigMap containing the above content and mount it as a volume into the gardenlet pod. Next, specify the environment variable IMAGEVECTOR_OVERWRITE, whose value must be the path to the file you just mounted:

apiVersion: v1
kind: ConfigMap
metadata:
  name: gardenlet-images-overwrite
  namespace: garden
data:
  images_overwrite.yaml: |
    images:
    - ...
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: gardenlet
  namespace: garden
spec:
  template:
    ...
    spec:
      containers:
      - name: gardenlet
        env:
        - name: IMAGEVECTOR_OVERWRITE
          value: /charts-overwrite/images_overwrite.yaml
        volumeMounts:
        - name: gardenlet-images-overwrite
          mountPath: /charts-overwrite
        ...
      volumes:
      - name: gardenlet-images-overwrite
        configMap:
          name: gardenlet-images-overwrite
  ...

Image Vectors for Dependent Components

The gardenlet is deploying a lot of different components that might deploy other images themselves. These components might use an image vector as well. Operators might want to customize the image locations for these transitive images as well, hence, they might need to specify an image vector overwrite for the components directly deployed by Gardener.

It is possible to specify the IMAGEVECTOR_OVERWRITE_COMPONENTS environment variable to the gardenlet that points to a file with the following content:

components:
- name: etcd-druid
  imageVectorOverwrite: |
    images:
    - name: etcd
      tag: v1.2.3
      repository: etcd/etcd
...

The gardenlet will, if supported by the directly deployed component (etcd-druid in this example), inject the given imageVectorOverwrite into the Deployment manifest. The respective component is responsible for using the overwritten images instead of its defaults.