World C2: Container Pipelines

Layer cache in CI

You will learn: to keep your kek lapis layers between runs, so builds get fast.

Checked with GitHub Actions 2026-10 on 31 Oct 2026

The problem

On your laptop, a rebuild takes 10 seconds. On the belt, every build takes 4 minutes. Why?

Try it

Even with a cache, this recipe bakes npm ci again after every code change. Move the lines so it stays cached when src/cart.js changes.

Each recipe line adds one cake layer. Put the lines in a good order, then build.

Dockerfile (the recipe)

FROM node:24-alpine
WORKDIR /app
COPY . .
COPY package.json package-lock.json ./
RUN npm ci --omit=dev
CMD ["node", "server.js"]

You built it once. Next, you change src/cart.js.

The cake (your image)

CMD ["node", "server.js"]0B
RUN npm ci --omit=dev12.8MB
COPY package.json package-lock.json ./53.2kB
COPY . .36.9kB
WORKDIR /app8.19kB
FROM node:24-alpine181MB

Watch

Tap the line that saves today's layers for next time.

0 of 1 found

The can live in the GitHub Actions cache. cache-from reads old layers. cache-to saves new ones. mode=max keeps middle stages too.

Try it

Press Run. Then press Run again, and watch the build station.

Run it twice. Watch the second run take a shortcut.

What happened on GitHub

Push to main

Workflow file .github/workflows/image.yml

1name: Image
2on:
3  push:
4    branches: [main]
5permissions:
6  contents: read
7jobs:
8  image:
9    runs-on: ubuntu-latest
10    steps:
11      - uses: docker/setup-buildx-action@v4
12      - uses: docker/build-push-action@v7
13        with:
14          tags: kedai-kancil:ci
15          cache-from: type=gha
16          cache-to: type=gha,mode=max

The line

Push to main · main

Predict

Now you add a package, so package.json changes. What bakes again on the belt?

Check

Good cache habit? Swipe right for yes, left for “needs work”.

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

1 / 4

Copy the package files and install before copying the code

You did it!

You can now keep your layer cache between runs.

Go deeper (optional)

GitHub deletes caches nobody used for a while. Each repo also has a size limit. type=registry keeps the cache in GHCR instead. Two images? Give each its own scope, like type=gha,scope=api.

Real rep (optional):

Real mission

In a public practice repo, add cache-from and cache-to with type=gha.
Push once. Note how long the build step takes.
Change one line of code and push again. Compare the times.

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