Docker multi-stage builds with Flask¶

When containerizing a Python application, it is standard practice to use a Docker multi-stage build. This technique separates the environment needed for development and building from the minimal environment required to run the application in production^[400-devops__09-Scripting-Language__python__introduction__part-4.http__README.md].

Base Image Configuration¶

The process typically begins by defining a base stage using a specific Python version, such as python:3.9.6-alpine3.13^[400-devops__09-Scripting-Language__python__introduction__part-4.http__README.md#L24-L25]. In a Flask workflow, this stage is often named dev and sets up the initial working directory^[400-devops__09-Scripting-Language__python__introduction__part-4.http__README.md#L24-L25].

Dependency Management¶

Flask is an external package that must be installed via pip^[400-devops__09-Scripting-Language__python__introduction__part-4.http__README.md]. To ensure consistency, dependencies are listed in a requirements.txt file^[400-devops__09-Scripting-Language__python__introduction__part-4.http__README.md]. Within the Docker build process, this file is copied into the image before the application code to leverage Docker layer caching, and pip install is executed to install the necessary libraries^[400-devops__09-Scripting-Language__python__introduction__part-4.http__README.md#L328-L329].

Application Runtime¶

The final stage of the Dockerfile is usually aliased as runtime^[400-devops__09-Scripting-Language__python__introduction__part-4.http__README.md#L327]. This stage creates a clean working directory (e.g., /app), copies in the installed dependencies from the build stage, and adds the application source code (e.g., app.py)^[400-devops__09-Scripting-Language__python__introduction__part-4.http__README.md#L328-L331].

Environment variables, such as FLASK_APP, are defined to configure the runtime, and the entry point is set to start the server, typically using flask run -h 0.0.0 -p 5000^[400-devops__09-Scripting-Language__python__introduction__part-4.http__README.md#L332-L334].

Volume Mounting¶

For data persistence, it is critical to separate application code from data directories. When running the container, volumes should be mounted to specific directories (e.g., /data) rather than the root application folder to prevent overwriting application files with configuration or data files^[400-devops__09-Scripting-Language__python__introduction__part-4.http__README.md#L345-L353].

Sources¶

^[400-devops__09-Scripting-Language__python__introduction__part-4.http__README.md]