How to debug Python apps inside a Docker Container with VS Code

Learn how you can use a debugger in VS Code inside a Docker Container to debug Python apps.

This article shows how you can can use a debugger in VS Code to debug Python apps inside a Docker Container.

#more

Step 1: Add debugpy¶

First, we need to add debugpy. An implementation of the Debug Adapter Protocol for Python maintained by Microsoft.

We can install it with

pip install debugpy

Then add this code snippet at the top of your code:

import debugpy
debugpy.listen(("0.0.0.0", 5678))

Optionally, we can also add these lines to wait with script execution until we've attached VS Code.

print("Waiting for client to attach...")
debugpy.wait_for_client()

Step 2: Run the container¶

Now, run the container and map the port:

docker run -p 5678:5678 your_image

Or if you use docker-compose:

services:
  app:
    ...
    ports:
      - 5678:5678
    ...

Step 3: Open VS Code and connect Debugger¶

In VS Code, click on Run -> Add Configuration -> Remote Attach and then leave the default configuration as localhost and port 5678.

This creates a launch.json file inside the .vscode folder that tells the debugger to attach to port 5678 where the remote debug server is running.

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Python: Remote Attach",
            "type": "python",
            "request": "attach",
            "connect": {
                "host": "localhost",
                "port": 5678
            },
            "pathMappings": [
                {
                    "localRoot": "${workspaceFolder}",
                    "remoteRoot": "."
                }
            ],
            "justMyCode": true
        }
    ]
}

You can now set breakpoints and then click on Run -> Start Debugging to start the debugging session. Enjoy!

Further Resources¶

• Article: Debugging for Dockerized ML applications in Python
• Talk: Best Practices for Compose-managed Python Apps