What is ArgoCD Image Updater and how does it automate container image updates?

ArgoCD Image Updater is an optional add-on controller that monitors container registries for new image tags and automatically updates the image tag references used by ArgoCD Applications — without requiring a CI pipeline to commit changes back to Git manually.

Image Updater watches Applications annotated with argocd-image-updater.argoproj.io/image-list. On each poll cycle it queries the container registry, determines the newest tag satisfying the configured update strategy, then updates the Application's image either by writing a commit back to Git (git write-back mode) or patching the Application's parameter overrides directly in ArgoCD (in-cluster mode).

metadata:
  annotations:
    argocd-image-updater.argoproj.io/image-list: myapp=docker.io/myorg/myapp
    argocd-image-updater.argoproj.io/myapp.update-strategy: semver
    argocd-image-updater.argoproj.io/myapp.allow-tags: regexp:^v[0-9]+\.[0-9]+\.[0-9]+$
    argocd-image-updater.argoproj.io/write-back-method: git

In git write-back mode, Image Updater commits the updated image tag to a dedicated branch or the tracked branch, creating a full audit trail in Git. ArgoCD then detects the commit and syncs normally, preserving GitOps principles.

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