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