Enable debugging in a Django project with Docker

Hi! In this post i’m going to show you how to debug your Django code with Docker.

In a Django project with 3 images (django, postgres and redis) you can't debug your code.

Our project run without any issue:

$ docker-compose up
Starting redis_1        ... done
Starting postgres_1     ... done
Starting celeryworker_1 ... done
Starting django_1       ... done
Starting flower_1       ... done
Starting celerybeat_1   ... done
Attaching to redis_1, postgres_1, celerybeat_1, django_1, celeryworker_1, flower_1
...
...
django_1        | Performing system checks...
django_1        |
django_1        | System check identified no issues (0 silenced).
django_1        | August 25, 2019 - 02:29:42
django_1        | Django version 2.0.9, using settings 'config.settings.local'
django_1        | Starting development server at http://0.0.0.0:8000/
django_1        | Quit the server with CONTROL-C.

But, if we put a breakpoint into our code (import pdb; pdb.set_trace()), we get this kind of error:

django_1        | Performing system checks...
django_1        |
django_1        | > /app/config/urls.py(12)<module>()
django_1        | -> path(settings.ADMIN_URL, admin.site.urls),
django_1        | (Pdb)
django_1        | Unhandled exception in thread started by <function check_errors.<locals>.wrapper at 0x7f959fef4400>
django_1        | Traceback (most recent call last):
django_1        |   File "/usr/local/lib/python3.6/site-packages/django/utils/autoreload.py", line 225, in wrapper
...
...
django_1        |   File "/app/config/urls.py", line 12, in <module>
django_1        |     path(settings.ADMIN_URL, admin.site.urls),
django_1        |   File "/app/config/urls.py", line 12, in <module>
django_1        |     path(settings.ADMIN_URL, admin.site.urls),
django_1        |   File "/usr/local/lib/python3.6/bdb.py", line 51, in trace_dispatch
django_1        |     return self.dispatch_line(frame)
django_1        |   File "/usr/local/lib/python3.6/bdb.py", line 70, in dispatch_line
django_1        |     if self.quitting: raise BdbQuit
django_1        | bdb.BdbQuit

What do we have to do to resolve this? We need to run django server in other terminal instance:

These are the steps:

1- Open other terminal instance
2- Run docker-compose ps to view running containers÷

$ docker-compose ps
django_1         /entrypoint /start               Up       0.0.0.0:8000->8000/tcp
postgres_1       docker-entrypoint.sh postgres    Up       5432/tcp
redis_1          docker-entrypoint.sh redis ...   Up       6379/tcp

3- Run docker rm -f django_1 to remove containers
4- Then, run docker-compose run --rm --service-ports django:

$ docker-compose run --rm --service-ports django
Starting postgres_1 ... done
PostgreSQL is available
Operations to perform:
  Apply all migrations: admin, auth, contenttypes, sessions
Running migrations:
  No migrations to apply.
Performing system checks...

System check identified no issues (0 silenced).
August 25, 2019 - 02:54:59
Django version 2.0.9, using settings 'config.settings.local'
Starting development server at http://0.0.0.0:8000/
Quit the server with CONTROL-C

5- Now, you can put a breakpoint! Save the changes and...

Performing system checks...

> /app/config/urls.py(12)<module>()
-> path(settings.ADMIN_URL, admin.site.urls),
(Pdb)

I hope you find it useful!