Container Images

Dynamic configuration of container images.

There are usually 2 different scenarios where Container Images need to be specified:

  1. When deploying third party applications like nginx, redis, … (e.g. via the Helm integration ).
    • In this case, image versions/tags rarely change, and if they do, this is an explicit change to the deployment. This means it’s fine to have the image versions/tags directly in the deployment manifests.
  2. When deploying your own applications.
    • In this case, image versions/tags might change very rapidly, sometimes multiple times per hour. Having these versions/tags directly in the deployment manifests can easily lead to commit spam and hard to manage multi-environment deployments.

kluctl offers a better solution for the second case.

images.get_image()

This is solved via a templating function that is available in all templates/resources. The function is part of the global images object and expects the following arguments:

images.get_image(image)

  • image
    • The image name/repository. It is looked up the list of fixed images.

The function will lookup the given image in the list of fixed images and return the last match.

Example deployment:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-deployment
spec:
  template:
    spec:
      containers:
      - name: c1
        image: "{{ images.get_image('registry.gitlab.com/my-group/my-project') }}"

Fixed images

Fixed images can be configured multiple methods:

  1. Command line argument --fixed-image
  2. Command line argument --fixed-images-file
  3. Target definition
  4. Global ‘images’ variable

Command line argument --fixed-image

You can pass fixed images configuration via the --fixed-image argument . Due to environment variables support in the CLI, you can also use the environment variable KLUCTL_FIXED_IMAGE_XXX to configure fixed images.

The format of the --fixed-image argument is --fixed-image image<:namespace:deployment:container>=result. The simplest example is --fixed-image registry.gitlab.com/my-group/my-project=registry.gitlab.com/my-group/my-project:1.1.2.

Command line argument --fixed-images-file

You can also configure fixed images via a yaml file by using --fixed-images-file /path/to/fixed-images.yaml. file:

images:
  - image: registry.gitlab.com/my-group/my-project
    resultImage: registry.gitlab.com/my-group/my-project:1.1.2

The file must contain a single root list named images with each entry having the following form:

images:
  - image: <image_name>
    resultImage: <result_image>
    # optional fields
    namespace: <namespace>
    deployment: <kind>/<name>
    container: <name>

image and resultImage are required. All the other fields are optional and allow to specify in detail for which object the fixed is specified.

Target definition

The target definition can optionally specify an images field that can contain the same fixed images configuration as found in the --fixed-images-file file.

Global ‘images’ variable

You can also define a global variable named images via one of the variable sources . This variable must be a list of the same format as the images list in the --fixed-images-file file.

This option allows to externalize fixed images configuration, meaning that you can maintain image versions outside the deployment project, e.g. in another Git repository .