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207 lines
3.3 KiB
Go
207 lines
3.3 KiB
Go
## 7.10 WORKDIR 指定工作目录
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### 基本语法
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```docker
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WORKDIR <工作目录路径>
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```
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`WORKDIR` 指定后续指令的工作目录。如果目录不存在，Docker 会自动创建。
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---
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### 基本用法
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```docker
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WORKDIR /app
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RUN pwd # 输出 /app
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RUN echo "hello" > world.txt # 创建 /app/world.txt
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COPY . . # 复制到 /app/
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```
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---
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### 为什么需要 WORKDIR
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#### 常见错误
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```docker
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## ❌ 错误：cd 在下一个 RUN 中无效
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RUN cd /app
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RUN echo "hello" > world.txt # 文件在根目录！
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```
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#### 原因分析
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```
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RUN cd /app
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↓
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启动容器 → cd /app（仅内存变化）→ 提交镜像层 → 容器销毁
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│
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↓ 工作目录未改变！
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RUN echo "hello" > world.txt
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↓
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启动新容器（工作目录在 /）→ 创建 /world.txt
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```
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每个 RUN 都在新容器中执行，**前一个 RUN 的内存状态（包括工作目录）不会保留**。
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#### 正确做法
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```docker
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## ✅ 正确：使用 WORKDIR
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WORKDIR /app
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RUN echo "hello" > world.txt # 创建 /app/world.txt
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```
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---
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### 相对路径
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WORKDIR 支持相对路径，基于上一个 WORKDIR：
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```docker
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WORKDIR /a
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WORKDIR b
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WORKDIR c
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RUN pwd # 输出 /a/b/c
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```
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---
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### 使用环境变量
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```docker
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ENV APP_HOME=/app
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WORKDIR $APP_HOME
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RUN pwd # 输出 /app
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```
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---
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### 多阶段构建中的 WORKDIR
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```docker
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## 构建阶段
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FROM node:20 AS builder
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WORKDIR /build
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COPY package*.json ./
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RUN npm install
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COPY . .
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RUN npm run build
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## 生产阶段
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FROM nginx:alpine
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WORKDIR /usr/share/nginx/html
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COPY --from=builder /build/dist .
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```
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---
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### 最佳实践
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#### 1. 尽早设置 WORKDIR
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```docker
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FROM node:20
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WORKDIR /app # 尽早设置
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COPY package*.json ./
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RUN npm install
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COPY . .
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CMD ["node", "server.js"]
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```
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#### 2. 使用绝对路径
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```docker
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## ✅ 推荐：绝对路径，意图明确
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WORKDIR /app
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## ⚠️ 避免：相对路径可能造成混淆
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WORKDIR app
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```
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#### 3. 不要用 RUN cd
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```docker
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## ❌ 避免
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RUN cd /app && echo "hello" > world.txt
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## ✅ 推荐
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WORKDIR /app
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RUN echo "hello" > world.txt
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```
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#### 4. 适时重置 WORKDIR
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```docker
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WORKDIR /app
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## ... 应用相关操作 ...
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WORKDIR /data
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## ... 数据相关操作 ...
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...
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```
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---
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### 与其他指令的关系
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| 指令 | WORKDIR 的影响 |
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|------|---------------|
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| `RUN` | 在 WORKDIR 中执行命令 |
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| `CMD` | 在 WORKDIR 中启动 |
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| `ENTRYPOINT` | 在 WORKDIR 中启动 |
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| `COPY` | 相对目标路径基于 WORKDIR |
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| `ADD` | 相对目标路径基于 WORKDIR |
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```docker
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WORKDIR /app
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RUN pwd # /app
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COPY . . # 复制到 /app
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CMD ["./start.sh"] # /app/start.sh
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```
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---
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### 运行时覆盖
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使用 `-w` 参数覆盖工作目录：
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```bash
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$ docker run -w /tmp myimage pwd
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/tmp
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```
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---
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### 本章小结
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| 要点 | 说明 |
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|------|------|
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| **作用** | 设置后续指令的工作目录 |
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| **语法** | `WORKDIR /path` |
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| **自动创建** | 目录不存在会自动创建 |
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| **持久性** | 影响后续所有指令，直到下次 WORKDIR |
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| **不要用** | `RUN cd /path`（无效） |
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### 延伸阅读
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- [COPY 复制文件](7.2_copy.md)：文件复制
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- [RUN 执行命令](../04_image/4.5_build.md)：执行构建命令
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- [最佳实践](../16_appendix/16.1_best_practices.md)：Dockerfile 编写指南
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