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在 GitHub Actions 中使用命名上下文

Table of contents

你可以定义 额外的构建上下文， 并在 Dockerfile 中通过 FROM name 或 --from=name 访问它们。当 Dockerfile 定义了同名阶段时， 该阶段会被覆盖。

在 GitHub Actions 中，这对于复用其他构建的结果，或在你的工作流中将某个镜像固定到特定标签很有用。

Pin image to a tag

用固定版本的镜像替换 alpine:latest：

# syntax=docker/dockerfile:1
FROM alpine
RUN echo "Hello World"
name: ci

on:
  push:

jobs:
  docker:
    runs-on: ubuntu-latest
    steps:
      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v4

      - name: Build
        uses: docker/build-push-action@v7
        with:
          build-contexts: |
            alpine=docker-image://alpine:3.23
          tags: myimage:latest

Use image in subsequent steps

默认情况下，Docker Setup Buildx action 使用 docker-container 作为构建驱动，因此构建出的 Docker 镜像不会自动加载。

借助命名上下文，你可以复用已构建的镜像：

# syntax=docker/dockerfile:1
FROM alpine
RUN echo "Hello World"
name: ci

on:
  push:

jobs:
  docker:
    runs-on: ubuntu-latest
    steps:
      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v4
        with:
          driver: docker

      - name: Build base image
        uses: docker/build-push-action@v7
        with:
          context: "{{defaultContext}}:base"
          load: true
          tags: my-base-image:latest

      - name: Build
        uses: docker/build-push-action@v7
        with:
          build-contexts: |
            alpine=docker-image://my-base-image:latest
          tags: myimage:latest

Using with a container builder

如上一节所示，在使用命名上下文构建时我们并没有使用默认的 docker-container driver。这是因为该驱动由于隔离性 无法从 Docker 存储中加载镜像。要解决这个问题，你可以使用本地注册表 在工作流中推送你的基础镜像：

# syntax=docker/dockerfile:1
FROM alpine
RUN echo "Hello World"
name: ci

on:
  push:

jobs:
  docker:
    runs-on: ubuntu-latest
    services:
      registry:
        image: registry:3
        ports:
          - 5000:5000
    steps:
      - name: Set up QEMU
        uses: docker/setup-qemu-action@v4

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v4
        with:
          # network=host driver-opt needed to push to local registry
          driver-opts: network=host

      - name: Build base image
        uses: docker/build-push-action@v7
        with:
          context: "{{defaultContext}}:base"
          tags: localhost:5000/my-base-image:latest
          push: true

      - name: Build
        uses: docker/build-push-action@v7
        with:
          build-contexts: |
            alpine=docker-image://localhost:5000/my-base-image:latest
          tags: myimage:latest