Automate image updates to Git

This guide walks you through configuring container image scanning and deployment rollouts with Flux.

For a container image you can configure Flux to:

• scan the container registry and fetch the image tags
• select the latest tag based on the defined policy (semver, calver, regex)
• replace the tag in Kubernetes manifests (YAML format)
• checkout a branch, commit and push the changes to the remote Git repository
• apply the changes in-cluster and rollout the container image

For production environments, this feature allows you to automatically deploy application patches (CVEs and bug fixes), and keep a record of all deployments in Git history.

Production CI/CD workflow

• DEV: push a bug fix to the app repository
• DEV: bump the patch version and release e.g. v1.0.1
• CI: build and push a container image tagged as registry.domain/org/app:v1.0.1
• CD: pull the latest image metadata from the app registry (Flux image scanning)
• CD: update the image tag in the app manifest to v1.0.1 (Flux cluster to Git reconciliation)
• CD: deploy v1.0.1 to production clusters (Flux Git to cluster reconciliation)

For staging environments, this features allow you to deploy the latest build of a branch, without having to manually edit the app deployment manifest in Git.

Staging CI/CD workflow

• DEV: push code changes to the app repository main branch
• CI: build and push a container image tagged as ${GIT_BRANCH}-${GIT_SHA:0:7}-$(date +%s)
• CD: pull the latest image metadata from the app registry (Flux image scanning)
• CD: update the image tag in the app manifest to main-2d3fcbd-1611906956 (Flux cluster to Git reconciliation)
• CD: deploy main-2d3fcbd-1611906956 to staging clusters (Flux Git to cluster reconciliation)

Prerequisites

You will need a Kubernetes cluster version 1.16 or newer and kubectl version 1.18. For a quick local test, you can use Kubernetes kind. Any other Kubernetes setup will work as well.

In order to follow the guide you’ll need a GitHub account and a personal access token that can create repositories (check all permissions under repo).

Export your GitHub personal access token and username:

export GITHUB_TOKEN=<your-token>
export GITHUB_USER=<your-username>

Install Flux

Install Flux with the image automation components:

flux bootstrap github \
  --components-extra=image-reflector-controller,image-automation-controller \
  --owner=$GITHUB_USER \
  --repository=flux-image-updates \
  --branch=main \
  --path=clusters/my-cluster \
  --read-write-key \
  --personal

The bootstrap command creates a repository if one doesn’t exist, and commits the manifests for the Flux components to the default branch at the specified path. It then configures the target cluster to synchronize with the specified path inside the repository.

Deploy a demo app

We’ll be using a tiny webapp called podinfo to showcase the image update feature.

Clone your repository with:

git clone https://github.com/$GITHUB_USER/flux-image-updates
cd flux-image-updates

Create a deployment for podinfo inside clusters/my-cluster:

cat <<EOF > ./clusters/my-cluster/podinfo-deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: podinfo
  namespace: default
spec:
  selector:
    matchLabels:
      app: podinfo
  template:
    metadata:
      labels:
        app: podinfo
    spec:
      containers:
        - name: podinfod
          image: ghcr.io/stefanprodan/podinfo:5.0.0
          imagePullPolicy: IfNotPresent
          ports:
            - name: http
              containerPort: 9898
              protocol: TCP
EOF

Commit and push changes to main branch:

git add -A && \
git commit -m "add podinfo deployment" && \
git push origin main

Tell Flux to pull and apply the changes or wait one minute for Flux to detect the changes on its own:

flux reconcile kustomization flux-system --with-source

Print the podinfo image deployed on your cluster:

$ kubectl get deployment/podinfo -oyaml | grep 'image:'
image: ghcr.io/stefanprodan/podinfo:5.0.0

Configure image scanning

Create an ImageRepository to tell Flux which container registry to scan for new tags:

flux create image repository podinfo \
--image=ghcr.io/stefanprodan/podinfo \
--interval=5m \
--export > ./clusters/my-cluster/podinfo-registry.yaml

The above command generates the following manifest:

apiVersion: image.toolkit.fluxcd.io/v1beta2
kind: ImageRepository
metadata:
  name: podinfo
  namespace: flux-system
spec:
  image: ghcr.io/stefanprodan/podinfo
  interval: 5m

For private images, you can create a Kubernetes secret in the same namespace as the ImageRepository with kubectl create secret docker-registry. Then you can configure Flux to use the credentials by referencing the Kubernetes secret in the ImageRepository:

kind: ImageRepository
spec:
  secretRef:
    name: regcred

Create an ImagePolicy to tell Flux which semver range to use when filtering tags:

flux create image policy podinfo \
--image-ref=podinfo \
--select-semver=5.0.x \
--export > ./clusters/my-cluster/podinfo-policy.yaml

The above command generates the following manifest:

apiVersion: image.toolkit.fluxcd.io/v1beta2
kind: ImagePolicy
metadata:
  name: podinfo
  namespace: flux-system
spec:
  imageRepositoryRef:
    name: podinfo
  policy:
    semver:
      range: 5.0.x

A semver range that includes stable releases can be defined with 1.0.x (patch versions only) or >=1.0.0 <2.0.0 (minor and patch versions). If you want to include pre-release e.g. 1.0.0-rc.1, you can define a range like: ^1.x-0 or >1.0.0-rc <2.0.0-rc.

Commit and push changes to main branch:

git add -A && \
git commit -m "add podinfo image scan" && \
git push origin main

Tell Flux to pull and apply changes:

flux reconcile kustomization flux-system --with-source

Wait for Flux to fetch the image tag list from GitHub container registry:

$ flux get image repository podinfo
NAME    LAST SCAN                       SUSPENDED       READY   MESSAGE
podinfo 2020-12-13T17:51:48+02:00       False           True    successful scan: found 13 tags

For debugging purposes, to see a sample of the tags scanned by the ImageRepository, a list of ten latest tags scanned by the ImageRepository resource can be seen in the status of the resource:

$ kubectl -n flux-system describe imagerepositories podinfo
...
Status:
  Canonical Image Name:  ghcr.io/stefanprodan/podinfo
  Last Scan Result:
    Latest Tags:
      latest
      6.3.3
      6.3.2
      6.3.1
      6.3.0
      6.2.3
      6.2.2
      6.2.1
      6.2.0
      6.1.8
    Scan Time:  2020-12-13T17:51:48Z
    Tag Count:  13
  Observed Exclusion List:
    ^.*\.sig$
  Observed Generation:  2
...

Find which image tag matches the policy semver range with:

$ flux get image policy podinfo
NAME    LATEST IMAGE                            READY   MESSAGE
podinfo ghcr.io/stefanprodan/podinfo:5.0.3      True    Latest image tag for 'ghcr.io/stefanprodan/podinfo' resolved to 5.0.3

Configure image updates

Edit the podinfo-deployment.yaml and add a marker to tell Flux which policy to use when updating the container image:

spec:
  containers:
  - name: podinfod
    image: ghcr.io/stefanprodan/podinfo:5.0.0 # {"$imagepolicy": "flux-system:podinfo"}

Create an ImageUpdateAutomation to tell Flux which Git repository to write image updates to:

flux create image update flux-system \
--interval=30m \
--git-repo-ref=flux-system \
--git-repo-path="./clusters/my-cluster" \
--checkout-branch=main \
--push-branch=main \
--author-name=fluxcdbot \
--author-email=fluxcdbot@users.noreply.github.com \
--commit-template="{{range .Changed.Changes}}{{print .OldValue}} -> {{println .NewValue}}{{end}}" \
--export > ./clusters/my-cluster/flux-system-automation.yaml

The above command generates the following manifest:

apiVersion: image.toolkit.fluxcd.io/v1beta2
kind: ImageUpdateAutomation
metadata:
  name: flux-system
  namespace: flux-system
spec:
  interval: 30m
  sourceRef:
    kind: GitRepository
    name: flux-system
  git:
    checkout:
      ref:
        branch: main
    commit:
      author:
        email: fluxcdbot@users.noreply.github.com
        name: fluxcdbot
      messageTemplate: '{{range .Changed.Changes}}{{print .OldValue}} -> {{println .NewValue}}{{end}}'
    push:
      branch: main
  update:
    path: ./clusters/my-cluster
    strategy: Setters

Commit and push changes to main branch:

git add -A && \
git commit -m "add image updates automation" && \
git push origin main

Note that the ImageUpdateAutomation runs all the policies found in its namespace at the specified interval.

Tell Flux to pull and apply changes:

flux reconcile kustomization flux-system --with-source

In a couple of seconds, Flux will push a commit to your repository with the latest image tag that matches the podinfo policy:

$ git pull && cat clusters/my-cluster/podinfo-deployment.yaml | grep "image:"
image: ghcr.io/stefanprodan/podinfo:5.0.3 # {"$imagepolicy": "flux-system:podinfo"}

Wait for Flux to apply the latest commit on the cluster and verify that podinfo was updated to 5.0.3:

$ watch "kubectl get deployment/podinfo -oyaml | grep 'image:'"
image: ghcr.io/stefanprodan/podinfo:5.0.3

You can check the status of the image automation objects with:

flux get images all --all-namespaces

Configure image update for custom resources

Besides Kubernetes native kinds (Deployment, StatefulSet, DaemonSet, CronJob), Flux can be used to patch image references in any Kubernetes custom resource stored in Git.

The image policy marker format is:

• {"$imagepolicy": "<policy-namespace>:<policy-name>"}
• {"$imagepolicy": "<policy-namespace>:<policy-name>:tag"}
• {"$imagepolicy": "<policy-namespace>:<policy-name>:name"}

These markers are placed inline in the target YAML, as a comment. The “Setter” strategy refers to kyaml setters which Flux can find and replace during reconciliation, when directed to do so by an ImageUpdateAutomation like the one above.

Here are some examples of using this marker in a variety of Kubernetes resources.

HelmRelease example:

apiVersion: helm.toolkit.fluxcd.io/v2
kind: HelmRelease
metadata:
  name: podinfo
  namespace: default
spec:
  values:
    image:
      repository: ghcr.io/stefanprodan/podinfo # {"$imagepolicy": "flux-system:podinfo:name"}
      tag: 5.0.0  # {"$imagepolicy": "flux-system:podinfo:tag"}

Tekton Task example:

apiVersion: tekton.dev/v1beta1
kind: Task
metadata:
  name: golang
  namespace: default
spec:
  steps:
    - name: golang
      image: docker.io/golang:1.15.6 # {"$imagepolicy": "flux-system:golang"}

Flux Kustomization example:

apiVersion: kustomize.toolkit.fluxcd.io/v1
kind: Kustomization
metadata:
  name: podinfo
  namespace: default
spec:
  images:
    - name: ghcr.io/stefanprodan/podinfo
      newName: ghcr.io/stefanprodan/podinfo # {"$imagepolicy": "flux-system:podinfo:name"}
      newTag: 5.0.0 # {"$imagepolicy": "flux-system:podinfo:tag"}

Kustomize config (kustomization.yaml) example:

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
- deployment.yaml
images:
- name: ghcr.io/stefanprodan/podinfo
  newName: ghcr.io/stefanprodan/podinfo # {"$imagepolicy": "flux-system:podinfo:name"}
  newTag: 5.0.0 # {"$imagepolicy": "flux-system:podinfo:tag"}

Push updates to a different branch

With .spec.git.push.branch you can configure Flux to push the image updates to different branch than the one used for checkout. If the specified branch doesn’t exist, Flux will create it for you.

kind: ImageUpdateAutomation
metadata:
  name: flux-system
spec:  
  git:
    checkout:
      ref:
        branch: main
    push:
      branch: flux-image-updates

You can use CI automation e.g. GitHub Actions such as Flux’s GitHub Actions Auto PR example to open a pull request against the checkout branch.

This way you can manually approve the image updates before they are applied on your clusters.

Configure the commit message

The .spec.git.commit.messageTemplate field is a string which is used as a template for the commit message.

The message template is a Go text template that lets you range over the objects and images e.g.:

kind: ImageUpdateAutomation
metadata:
  name: flux-system
spec:
  git:
    commit:
      messageTemplate: |
        Automated image update

        Automation name: {{ .AutomationObject }}

        Files:
        {{ range $filename, $_ := .Changed.FileChanges -}}
        - {{ $filename }}
        {{ end -}}

        Objects:
        {{ range $resource, $changes := .Changed.Objects -}}
        - {{ $resource.Kind }} {{ $resource.Name }}
          Changes:
        {{- range $_, $change := $changes }}
            - {{ $change.OldValue }} -> {{ $change.NewValue }}
        {{ end -}}
        {{ end -}}        
      author:
        email: fluxcdbot@users.noreply.github.com
        name: fluxcdbot

Trigger image updates with webhooks

You may want to trigger a deployment as soon as a new image tag is pushed to your container registry. In order to notify the image-reflector-controller about new images, you can setup webhook receivers.

First generate a random string and create a secret with a token field:

TOKEN=$(head -c 12 /dev/urandom | shasum | cut -d ' ' -f1)
echo $TOKEN

kubectl -n flux-system create secret generic webhook-token \	
--from-literal=token=$TOKEN

Define a receiver for DockerHub:

apiVersion: notification.toolkit.fluxcd.io/v1
kind: Receiver
metadata:
  name: podinfo
  namespace: flux-system
spec:
  type: dockerhub
  secretRef:
    name: webhook-token
  resources:
    - kind: ImageRepository
      name: podinfo

The notification-controller generates a unique URL using the provided token and the receiver name/namespace.

Find the URL with:

$ kubectl -n flux-system get receiver/podinfo

NAME      READY   STATUS
podinfo   True    Receiver initialised with URL: /hook/bed6d00b5555b1603e1f59b94d7fdbca58089cb5663633fb83f2815dc626d92b

Log in to DockerHub web interface, go to your image registry Settings and select Webhooks. Fill the form “Webhook URL” by composing the address using the receiver LB and the generated URL http://<LoadBalancerAddress>/<ReceiverURL>.

Incident management

Suspend automation

During an incident you may wish to stop Flux from pushing image updates to Git.

You can suspend the image automation directly in-cluster:

flux suspend image update flux-system

Or by editing the ImageUpdateAutomation manifest in Git:

kind: ImageUpdateAutomation
metadata:
  name: flux-system
  namespace: flux-system
spec:
  suspend: true

Once the incident is resolved, you can resume automation with:

flux resume image update flux-system

If you wish to pause the automation for a particular image only, you can suspend/resume the image scanning:

flux suspend image repository podinfo

Revert image updates

Assuming you’ve configured Flux to update an app to its latest stable version:

flux create image policy podinfo \
--image-ref=podinfo \
--select-semver=">=5.0.0"

If the latest version e.g. 5.0.1 causes an incident in production, you can tell Flux to revert the image tag to a previous version e.g. 5.0.0 with:

flux create image policy podinfo \
--image-ref=podinfo \
--select-semver=5.0.0

Or by changing the semver range in Git:

kind: ImagePolicy
metadata:
  name: podinfo
  namespace: flux-system
spec:
  policy:
    semver:
      range: 5.0.0

Based on the above configuration, Flux will patch the podinfo deployment manifest in Git and roll out 5.0.0 in-cluster.

When a new version is available e.g. 5.0.2, you can update the policy once more and tell Flux to consider only versions greater than 5.0.1:

flux create image policy podinfo \
--image-ref=podinfo \
--select-semver=">5.0.1"

ImageRepository cloud providers authentication

Two methods are available for authenticating container registers as ImageRepository resources in Flux:

• Automated authentication mechanisms (where the controller retrieves the credentials itself and is only available for the three major cloud providers), or
• a CronJob which does not rely on native platform support in Flux, (instead storing credentials as Kubernetes secrets which are periodically refreshed.)

Native authentication mechanisms have been implemented in Flux for the three major cloud providers, but they have to be set in the individual ImageRepository resources. Please see individual sections on how to do this.

ImagePolicy Examples

Select the latest main branch build tagged as ${GIT_BRANCH}-${GIT_SHA:0:7}-$(date +%s) (numerical):

kind: ImagePolicy
spec:
  filterTags:
    pattern: '^main-[a-fA-F0-9]+-(?P<ts>.*)'
    extract: '$ts'
  policy:
    numerical:
      order: asc

A more strict filter would be ^main-[a-fA-F0-9]+-(?P<ts>[1-9][0-9]*). Before applying policies in-cluster, you can validate your filters using regex101.com.

Select the latest stable version (semver):

kind: ImagePolicy
spec:
  policy:
    semver:
      range: '>=1.0.0'

Select the latest stable patch version in the 1.x range (semver):

kind: ImagePolicy
spec:
  policy:
    semver:
      range: '>=1.0.0 <2.0.0'

Select the latest version including pre-releases (semver):

kind: ImagePolicy
spec:
  policy:
    semver:
      range: '>=1.0.0-0'

Select the latest release candidate (semver):

kind: ImagePolicy
spec:
  filterTags:
    pattern: '.*-rc.*'
  policy:
    semver:
      range: '^1.x-0'

Select the latest version by extracting the semver from tags in the format <semver>-<distro> e.g. Redis on DockerHub:

kind: ImagePolicy
spec:
  filterTags:
    pattern: '^(?P<semver>[0-9]*\.[0-9]*\.[0-9]*)-(alpine[0-9]*\.[0-9]*)'
    extract: '$semver'
  policy:
    semver:
      range: '>=1.0.0'

Select the latest release tagged as RELEASE.<RFC3339-TIMESTAMP> e.g. Minio (alphabetical):

kind: ImagePolicy
spec:
  filterTags:
    pattern: '^RELEASE\.(?P<timestamp>.*)Z$'
    extract: '$timestamp'
  policy:
    alphabetical:
      order: asc