GitHub Action镜像构建问题：PR仅构建，合并/发布才推送到GHCR

GitHub Actions中，环境变量会自动将布尔值转换为字符串类型。你定义的DO_PUSH是布尔表达式，实际存储的是"true"或"false"字符串，而非布尔值。当你用if: env.DO_PUSH == true时，是在比较字符串和布尔值，结果永远不相等，所以触发推送的步骤不会执行；而env.DO_PUSH != true相当于字符串不等于布尔值，结果永远为真，所以"Only build"步骤始终运行。

方案1：直接在if条件中使用原表达式（推荐） #

去掉DO_PUSH环境变量，直接在需要判断的步骤里使用布尔表达式，避免类型转换问题：

name: Build

on:
  push:
    branches: ['main']
    tags: ['v*']
  pull_request:
    branches: ['main']

jobs:
  build-and-push:
    # ...
    
    steps:
      - 
        name: Checkout repository
        uses: actions/checkout@v3
      - 
        name: Log in to GHCR
        if: github.ref == 'refs/heads/main' || github.event_name == 'release'
        uses: docker/login-action@v2
        # ...
      - 
        name: Get Docker metadata
        if: github.ref == 'refs/heads/main' || github.event_name == 'release'
        id: meta
        uses: docker/metadata-action@v4
        # ...
      - 
        name: Only build
        if: github.ref != 'refs/heads/main' && github.event_name != 'release'
        uses: docker/build-push-action@v4
        with:
          context: .
          push: false
      - 
        name: Build and push
        if: github.ref == 'refs/heads/main' || github.event_name == 'release'
        uses: docker/build-push-action@v4
        with:
          context: .
          push: true
          # ...

方案2：保留环境变量，改用字符串比较 #

如果坚持使用DO_PUSH环境变量，需要在if条件中比较字符串值：

name: Build

on:
  push:
    branches: ['main']
    tags: ['v*']
  pull_request:
    branches: ['main']

env:
  # ...
  DO_PUSH: ${{ github.ref == 'refs/heads/main' || github.event_name == 'release' }}

jobs:
  build-and-push:
    # ...
    
    steps:
      - 
        name: Checkout repository
        uses: actions/checkout@v3
      - 
        name: Log in to GHCR
        if: env.DO_PUSH == 'true'
        uses: docker/login-action@v2
        # ...
      - 
        name: Get Docker metadata
        if: env.DO_PUSH == 'true'
        id: meta
        uses: docker/metadata-action@v4
        # ...
      - 
        name: Only build
        if: env.DO_PUSH != 'true'
        uses: docker/build-push-action@v4
        with:
          context: .
          push: false
      - 
        name: Build and push
        if: env.DO_PUSH == 'true'
        uses: docker/build-push-action@v4
        with:
          context: .
          push: true
          # ...

注意你的触发规则中，push事件包含了tags: ['v*']，但当前判断条件里只检查了github.event_name == 'release'，如果是通过推送标签触发的Action，github.event_name是push而非release，这会导致标签推送时无法触发推送步骤。如果需要支持标签推送时也推送镜像，需要把判断条件调整为：

github.ref == 'refs/heads/main' || startsWith(github.ref, 'refs/tags/v')

或者对应到环境变量的定义：

DO_PUSH: ${{ github.ref == 'refs/heads/main' || startsWith(github.ref, 'refs/tags/v') }}

内容的提问来源于stack exchange，提问作者theo