flux-mirror

README

flux-mirror

Flux Mirror is a CLI for mirroring Helm charts, OCI artifacts and container images between registries using a declarative approach.

The intended use case is feeding an internal mirror registry that backs Flux OCIRepository and Kubernetes Deployments, so clusters never reach out to upstream registries at reconcile time.

It also enables migration away from HTTP/S HelmRepository sources: chart versions are republished as OCI Helm artifacts that HelmRelease consumes via an OCIRepository in spec.chartRef, dropping the runtime dependency on upstream chart repositories.

[!NOTE] This repository is in early development and the plugin system is not yet available in a stable release of Flux. Instructions for installing and using flux-mirror as a Flux CLI plugin will be added here once RFC-0013 ships in Flux 2.9 or later.

Features

• OCI artifacts — mirror container images, OCI Helm charts, Flux OCI artifacts, and any other OCI-addressable artifact between registries. Manifests and blobs are copied byte-for-byte; multi-arch manifest lists are mirrored as a whole, no platform filtering.
• Helm charts — mirror charts from HTTP/S Helm repositories to an OCI registries. Chart bytes are re-published as a deterministic Helm-OCI artifact, so drift detection on re-runs is content-based and stable.
• OCI 1.1 referrers — opt-in mirror of cosign signatures, SBOMs, and attestations attached to artifacts.
• Selector pipeline — for OCI artifacts, a four-step regex → semver → sort → top-N filter. For charts, a semver constraint plus top-N. Sort by semver, alphabetical, or numerical.
• Idempotent — destination digests are compared per tag/version. Re-runs copy only what's missing or drifted.
• Drift gating — destination drift (different content under the same tag) is reported as a distinct outcome and exit code, so audit pipelines can differentiate "out of date" from "mutated tags".
• Ambient auth — credentials come from ~/.docker/config.json and the configured credential helpers (ACR, ECR, GAR, etc.). One docker login covers source and destination.
• Structured output — text and yaml/json for downstream tooling, plus a verbose mode that streams every blob and manifest digest for diagnosing TLS, auth, or push failures.

Install

Download the binary for your platform from the releases page, or build from source:

go install github.com/fluxcd/flux-mirror/cmd/flux-mirror@latest

Quickstart

Authenticate once against the destination and optionally source registries:

docker login ghcr.io

Write a config file describing what to mirror:

# flux-mirror.yaml
apiVersion: mirror.fluxcd.io/v1alpha1
kind: Config
charts:
  - name: external-dns
    source: https://kubernetes-sigs.github.io/external-dns/
    destination: oci://ghcr.io/my-org/charts
    version: ">=1.15.0"
    limit: 3
artifacts:
  - source: registry.k8s.io/external-dns/external-dns
    destination: ghcr.io/my-org/external-dns
    selector:
      semver: ">=0.15.0"
      limit: 3
    includeReferrers: true

Run the sync:

flux-mirror sync flux-mirror.yaml

You can also read the config from stdin:

flux-mirror sync - < flux-mirror.yaml

Preview without writing:

flux-mirror sync flux-mirror.yaml --dry-run

Force a resync of drifted tags e.g. latest:

flux-mirror sync flux-mirror.yaml --overwrite

See examples/ for more configurations and docs/sync.md for the full flag reference.

Running in CI

flux-mirror sync is designed for unattended runs. The exit code separates real failures from drift, so a CI gate can react to each independently:

Code	Meaning
0	Clean run, every tag was copied or skipped as expected.
1	At least one tag job failed (network error, push rejected, retries exhausted).
2	No failures, but at least one tag drifted with overwrite: false (configurable with --drift-exit-code).

The --no-progress flag suppresses the live spinner so log output stays clean in CI:

flux-mirror sync flux-mirror.yaml --no-progress

When the destination registry is known to be immutable, drift can be reported without failing the CI job:

flux-mirror sync flux-mirror.yaml --no-progress --drift-exit-code=0

For downstream tooling, emit a structured report:

flux-mirror sync flux-mirror.yaml -o json | jq '.entries[].outcomes'

GitHub Actions

The fluxcd/flux-mirror/actions/setup composite action installs the CLI on Ubuntu, macOS, and Windows runners.

Example workflow:

name: mirror-charts

on:
  schedule:
    - cron: "0 */6 * * *"
  workflow_dispatch:

jobs:
  sync:
    runs-on: ubuntu-latest
    permissions:
      contents: read
      packages: write
    steps:
      - name: Checkout
        uses: actions/checkout@v6
      - name: Setup Flux Mirror CLI
        uses: fluxcd/flux-mirror/actions/setup@main
      - name: Login to GHCR
        uses: docker/login-action@v4
        with:
          registry: ghcr.io
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}
      - name: Sync Kubernetes SIGs Charts
        run: flux-mirror sync kubernetes-sigs.yaml --no-progress

Docker

The ghcr.io/fluxcd/flux-mirror image can be used in container-based CI pipelines:

docker run --rm \
  -e DOCKER_CONFIG=/.docker \
  -v "$PWD/flux-mirror.yaml:/config.yaml:ro" \
  -v "$HOME/.docker/config.json:/.docker/config.json:ro" \
  ghcr.io/fluxcd/flux-mirror:latest sync /config.yaml --no-progress

Kubernetes

To run flux-mirror sync from inside a cluster on a schedule, see the examples/cronjob.yaml manifest. It bundles a ConfigMap with the sync config and a CronJob that mounts the destination registry credentials from a Secret created via flux create secret oci.

Commands

Command	Description
flux-mirror sync [CONFIG]	Mirror Helm charts and OCI artifacts described by a YAML config.
flux-mirror version	Print the CLI version.

Run flux-mirror <command> --help for the full flag list.

Documentation

• Sync command reference — flags, output modes, outcomes, exit codes, and example invocations.
• Config specification — YAML schema for artifacts and charts entries, selector pipeline, overwrite semantics, defaults.
• Examples — runnable configs for common mirror scenarios.

License

The Flux Mirror project is Apache 2.0 licensed and accepts contributions via GitHub pull requests.