Debug python service in container

What if you have a python service (flask, Django,...) running in a docker container and you want to debug the code.

There is a way to do that debugpy

Tools required:

1. vs code
2. docker

Follow the following steps to debug the code:

1. add debugpy to the requirements file

debugpy

1. forward the port for debugging from the docker container

   1. If creating a container from Dockerfile then expose the port following way:
      https://docs.docker.com/engine/reference/builder/#expose
      

      
      EXPOSE 10001
      
      

   2. If using docker-compose then expose the port following way:
      

      version: "3.7"
      services:
        python-service:
          container_name: python-service
          build:
            context: .
            args:
              DEV: 1
          command: sh setup/run-backend-docker.sh --reload
          restart: on-failure:5
          volumes:
            - ./:/usr/src/app/
            - /var/run/docker.sock:/var/run/docker.sock    
          ports:
            - 10001:10001
      

      Here code will decide in /usr/src/app/ inside docker container.

2. Open the code in vs code and create a folder with name .vscode in parent folder. And create the following 2 files inside it.

   1. launch.json
      

      {
          // 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": [
              { // simple attach to running container - works good
                  "name": "Python Attach",
                  "type": "python",
                  "request": "attach",
                  "port": 10001,
                  "host": "localhost",
                  "pathMappings": [
                      {
                          "localRoot": "${workspaceFolder}/",
                          "remoteRoot": "/usr/src/app/"
                      }
                  ]
              }
          ]
      
      

   2. tasks.json
      

   {
       "label": "docker-compose-start",
       "type": "shell",
       "command": "docker compose -f docker-compose.dev.yml up -d --build -d",
       "isBackground": true,
       "problemMatcher": [
         {
           "pattern": [{ "regexp": ".", "file": 1, "location": 2, "message": 3, }],
           "background": {
             "activeOnStart": true,
             "beginsPattern": "^(Building py-service)$",
             "endsPattern": "^(Creating|Recreating|Starting) (py-container) ... (done)$",
           }
         },
       ],
     }
   

   Here we are using docker-compose to create a python service. That's why in the command we specified docker-compose -f docker-compose.dev.yml up -d --build -d, if you are using Dockerfile use the following command: docker run —name container_name image_name.

   Reference: https://docs.docker.com/engine/reference/run/

3. Now, let's add a listener which will keep track of your button and enables when you will press F5 (in vs code) to debug and attach the debugger.
   
   For that add the following line before our service app
   
   

import multiprocessing

if multiprocessing.current_process().pid > 1:
    import debugpy

    debugpy.listen(("0.0.0.0", 10001))
    print("⏳ VS Code debugger can now be attached, press F5 in VS Code ⏳", flush=True)
    debugpy.wait_for_client()
    print("🎉 VS Code debugger attached, enjoy debugging 🎉", flush=True)

app = create_app()

Reference :

1. debug flask
2. debug flask in docker-compose