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docs: named contexts
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# Named contexts | ||
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You can define [additional build contexts](https://docs.docker.com/engine/reference/commandline/buildx_build/#build-context) | ||
that can be accessed in your Dockerfile with `FROM name` or `--from=name`. When | ||
Dockerfile defines a stage with the same name it is overwritten. | ||
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This can be useful with GitHub Actions to reuse results from other builds or | ||
pin an image to a spcific tag in your workflow. | ||
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## Pin image to a specific tag | ||
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Replace `alpine:latest` with a pinned one: | ||
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```dockerfile | ||
# syntax=docker/dockerfile:1 | ||
FROM alpine | ||
RUN echo "Hello World" | ||
``` | ||
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```yaml | ||
name: ci | ||
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on: | ||
push: | ||
branches: | ||
- 'main' | ||
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jobs: | ||
docker: | ||
runs-on: ubuntu-latest | ||
steps: | ||
- | ||
name: Checkout | ||
uses: actions/checkout@v3 | ||
- | ||
name: Set up Docker Buildx | ||
uses: docker/setup-buildx-action@v2 | ||
- | ||
name: Build | ||
uses: docker/build-push-action@v3 | ||
with: | ||
context: . | ||
build-contexts: | | ||
alpine=docker-image://alpine:3.16 | ||
tags: myimage:latest | ||
``` | ||
## Usage of the built image in other build steps | ||
By default, the [`setup-buildx` action](https://github.com/docker/setup-buildx-action#about) | ||
uses `docker-container` as a build driver, so built Docker images are not | ||
available in the builder container. | ||
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With named contexts you can reuse the built image: | ||
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||
```dockerfile | ||
# syntax=docker/dockerfile:1 | ||
FROM alpine | ||
RUN echo "Hello World" | ||
``` | ||
|
||
```yaml | ||
name: ci | ||
on: | ||
push: | ||
branches: | ||
- 'main' | ||
jobs: | ||
docker: | ||
runs-on: ubuntu-latest | ||
steps: | ||
- | ||
name: Checkout | ||
uses: actions/checkout@v3 | ||
- | ||
name: Set up Docker Buildx | ||
uses: docker/setup-buildx-action@v2 | ||
- | ||
name: Build base image | ||
uses: docker/build-push-action@v3 | ||
with: | ||
context: base | ||
load: true | ||
tags: my-base-image:latest | ||
- | ||
name: Build | ||
uses: docker/build-push-action@v3 | ||
with: | ||
context: . | ||
build-contexts: | | ||
alpine=docker-image://my-base-image:latest | ||
tags: myimage:latest | ||
``` |