Docker运行时出现ModuleNotFoundError: No module named 'flask'问题求助

问题根源 #

你采用了Docker多阶段构建，但仅将第一阶段（backend-builder）的代码目录/app复制到了第二阶段，没有同步该阶段安装的Python依赖。Flask等依赖是安装在backend-builder阶段Python环境的site-packages目录下，而非/app内，导致第二阶段运行容器时找不到对应的模块。

解决方案 #

方案1：完善多阶段构建，同步依赖

修改Dockerfile，在第二阶段同时复制代码和已安装的依赖文件：

# Use an official Python runtime as the base image
FROM python:3.9 AS backend-builder

# Set the working directory in the container
WORKDIR /app

# Copy the backend code into the container
COPY ./backend /app

# Install Python dependencies, including Flask
RUN pip install -r requirements.txt

#------------------Stage 1 Ends----------------------
#------------------Stage 2 Start---------------------
FROM python:3.9-slim-buster

# Set the working directory in the container
WORKDIR /app

# 复制代码和已安装的依赖包、可执行文件
COPY --from=backend-builder /app /app
COPY --from=backend-builder /usr/local/lib/python3.9/site-packages /usr/local/lib/python3.9/site-packages
COPY --from=backend-builder /usr/local/bin /usr/local/bin

# Expose the port
EXPOSE 5000

# Command to run the application
CMD ["python", "app.py"]

方案2：改用单阶段构建（适合对镜像体积要求不高的场景）

如果不需要极致压缩镜像大小，可简化为单阶段构建，避免依赖同步问题：

# Use an official Python runtime as the base image
FROM python:3.9-slim-buster

# Set the working directory in the container
WORKDIR /app

# Copy the backend code into the container
COPY ./backend /app

# Install Python dependencies, including Flask
RUN pip install -r requirements.txt

# Expose the port
EXPOSE 5000

# Command to run the application
CMD ["python", "app.py"]

验证步骤 #

1. 确认requirements.txt中包含Flask依赖（例如：Flask>=2.0.0）
2. 重新构建镜像：docker build -t my-flask-app .
3. 启动容器：docker run -p 5000:5000 my-flask-app

内容的提问来源于stack exchange，提问作者parmar pavan