How does Renovate update Docker image versions in Dockerfiles?

Renovate's dockerfile manager extracts FROM image references and raises PRs when newer tags are available. It supports both tag-based and digest-based pinning.

# Dockerfile — Renovate parses FROM lines
FROM node:20.11.0-alpine3.19
# → PR to update to node:20.12.0-alpine3.19

# Digest pinning (immutable)
FROM node:20@sha256:a1b2c3d4...  # Renovate updates digest when node:20 changes

{
  "packageRules": [
    {
      "matchManagers": ["dockerfile"],
      "matchPackageNames": ["node"],
      "allowedVersions": "20",
      "matchUpdateTypes": ["minor", "patch"],
      "automerge": true
    }
  ],
  "digest": {
    "enabled": true,
    "automerge": true
  }
}

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