Debugging Python within Docker

Often you need to run debugger within docker. It many cases it looks like this:

import pdb; pdb.set_trace()

Or:

import ipdb; ipdb.set_trace()

The following method works well in combination with docker-compose up:

1. Add the following line to your docker .yml file

stdin_open: true
tty: true

Example:

services:
  backend:
    stdin_open: true
    tty: true
    build: backend/
    command: python manage.py runserver 0.0.0.0:8000
    volumes:
      - ./backend:/backend
    ports:
      - "8000:8000"
    expose:
      - "8000"

2. Attach your running container

Running the docker ps command:

docker ps

And you would get something like this:

CONTAINER ID        IMAGE               COMMAND
abcdef012345        frontend            "npm run start"
ghijkl678910        backend             "python manage.py ..."

Note the backend <container id>.

Then run the docker attach command:

docker attach ghijkl678910

Now you can add pdb/ipdb set_trace statements in your code:

def view_index(request):
    # ...
    import ipdb; ipdb.set_trace()
    # ...

If you somehow get errors on Python 2.7, try replacing pdb/ipdb with pdbpp (pip install pdbpp).