World C2: Container Pipelines

Smart tags with metadata-action

You will learn: to label every image with its branch, version and commit.

Checked with GitHub Actions 2026-10 on 31 Oct 2026

The problem

The shop freezer holds 40 packs, all labelled latest. One pack made a customer sick. Which pack was it?

Watch

Tap the rule that writes the batch code: the commit.

0 of 1 found

are labels on the pack. docker/metadata-action writes them for you. Each rule adds a label when it fits the event.

Watch

Pick an event. Press Run and watch the line.

The metadata step prints the tags for the event you pick: push to main, a pull request, or a version tag.

What happened on GitHub

Push to mainPull requestPush tag v1.2.0

Workflow file .github/workflows/tags.yml

1name: Tags
2on:
3  push:
4    branches: [main]
5    tags: ['v*']
6  pull_request:
7permissions:
8  contents: read
9jobs:
10  tags:
11    runs-on: ubuntu-latest
12    steps:
13      - id: meta
14        uses: docker/metadata-action@v6
15        with:
16          images: ghcr.io/you/kedai-kancil
17          tags: |
18            type=ref,event=branch
19            type=ref,event=pr
20            type=semver,pattern={{version}}
21            type=sha

The line

Push to main · main

Pick an event and press Run. Then tap the station to read its log. The log lists the tags. Try all three events.

Try it

Which event makes which tag?

Drag a card into a box. Or tap the card, then tap the box.

Predict

You push the tag v1.3.0-rc.1, a test release. Which tags appear?

Check

Swipe right if the tag is good for production. Swipe left if it needs work.

Swipe right for good, left for needs work. Or use the buttons.

1 / 4kedai-kancil:1.2.0

You did it!

You can now give every image clear, traceable tags.

Go deeper (optional)

Add type=semver,pattern={{major}}.{{minor}} to also get 1.2. Set flavor: latest=false to stop latest. metadata-action also writes labels: pass labels: ${{ steps.meta.outputs.labels }} to the build.

Real rep (optional), in a public practice repo:

Real mission

Add the metadata step from this lesson to your image workflow.
Make a version tag.
git tag v0.1.0
Push the tag.
git push origin v0.1.0
Open the run and read the tags in the metadata step.

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