Debug python application running in Docker

Question

I've just recently begun trying to wrap my head around Docker and have managed to get a development machine up and running. What i'm now trying to do is to be able to use the debugger in Visual Studio Code in my python application (specifically Django).

I've tried following the limited documentation of the python extension for VS Code which explains the parameters for remote debugging.

Dockerfile

FROM python:3.5.2
RUN apt-get update \
--no-install-recommends && rm -rf /var/lib/apt/lists/* \
&& mkdir -p /code \
EXPOSE 8000
WORKDIR /code
COPY requirements.txt /code
RUN /bin/bash --login -c "pip install -r requirements.txt"
ADD . /code
CMD []

docker-compose.yml

version: '2'
services:
    db:
        image: postgres
    web:
        build: .
        volumes:
            - .:/code
        ports:
            - "8000:8000"
        command: bash -c "./wait-for-it.sh db:5432 && python manage.py migrate && python manage.py runserver 0.0.0.0:8000 --noreload"
        depends_on:
            - db

launch.json

{
    "name": "Attach (Remote Debug)",
    "type": "python",
    "request": "attach",
    "localRoot": "${workspaceRoot}",
    "remoteRoot": "/code",
    "port": 8000,
    "secret": "debug_secret",
    "host": "localhost"
}

I've also added the line ptvsd.enable_attach("debug_secret", address = ('0.0.0.0', 8000)) to one of the project files

The Issue

When ever I start the debugger nothing happens and it looks like VS Code is waiting for a breakpoint to hit. But it never does.

Any ideas?

EDIT: Minor update

I have tried using different ports for the debugger aswell as exposing the new ports in docker-compose.yml without any success. It looks like the attach is successfull because the debugger doesn't crash but no breakpoint is triggered. I'm really stuck on this one.

Solution

See answer from theBarkman. I'll add that I was unable to use a secret to get this working. I did the following:

manage.py

import ptvsd
ptvsd.enable_attach(secret=None, address=('0.0.0.0', '3000'))

launch.json

{
        "name": "Attach Vagrant",
        "type": "python",
        "request": "attach",
        "localRoot": "${workspaceRoot}",
        "remoteRoot": "/code",
        "port": 3000,
        "secret": "",
        "host":"localhost"
    }

theBarkman · Accepted Answer · 2017-03-16 23:09:35Z

4

I've had the most success remote debugging dockerized Django projects by throwing the ptvsd code into my manage.py file and turning off Django's live code reload.

Since Django essentially spins up 2 servers when you runserver (one for that live code reloading, and the other for the actual app server`, ptvsd seems to get really confused which server it should watch. I could sort of get it to work by waiting for attachment, try/excepting the enable_attach method or breaking into the debugger - but breakpoints would never work, and I could only seem to debug a single file at a time.

If you use the django flag --noreload when spinning up the server, you can throw the ptvsd inside the manage.py file without all the waiting / breaking into the debugger nonsense, and enjoy a much more robust debugging experience.

manage.py:

import ptvsd
ptvsd.enable_attach(secret='mah_secret', address=('0.0.0.0', 3000))

run teh server:

python manage.py runserver 0.0.0.0:8000 --noreload

Hope this helps!

answered Mar 16, 2017 at 23:09

theBarkman

1314 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Mattias Over a year ago

This helped me a lot! I'll mark this as the solution but I should add that I could not get ptvsd.enable_attach to work with a secret. I solved this by setting secret=None and secret="" in launch.json.

theBarkman Over a year ago

That's strange, I've never had issues with the secret portion of the attach. Glad you got it working though! Goes without saying, but make sure that doesn't get accidentally deployed without a secret ;) lol

Community · Accepted Answer · 2020-06-20 09:12:55Z

3

I was trying to do something very similar to you and came across this issue/comment:

https://github.com/DonJayamanne/pythonVSCode/issues/252#issuecomment-245566383

In there it describes that in order to use breakpoints you need to use the ptvsd.break_into_debugger() function.

As an example:

import ptvsd
ptvsd.enable_attach(secret='my_secret',address = ('0.0.0.0', 3000))
ptvsd.wait_for_attach()
ptvsd.break_into_debugger()

As soon as I added this in my python script, my breakpoints worked. Hopefully it's of some use.

Edit Jan 24, 2017

In my DockerFile I installed ptvsd:

FROM kaixhin/theano
RUN pip install ptvsd
WORKDIR /src
EXPOSE 3000
ENTRYPOINT ["python","src/app.py"]
COPY . /src

It looks like your installing dependencies via your requirements.txt file, is ptvsd in your requirements.txt?

edited Jun 20, 2020 at 9:12

CommunityBot

11 silver badge

answered Jan 11, 2017 at 20:05

Colter McQuay

862 bronze badges

5 Comments

Mattias Over a year ago

Thanks! I'll try this when I get home

Mattias Over a year ago

Couldn't get it to work... Maybe i'm doing something wrong. Where have you placed your ptvsd function calls (which file)?

Colter McQuay Over a year ago

@Mattias I just added a reference of my DockerFile, are you installing ptvsd within your docker container?

Mattias Over a year ago

what I meant was, where do I put the ptvsd function calls? Do i need to but it in every file or only a single file? Could you maybe show the entire code where you use ptvsd? Thanks

Mattias Over a year ago

I think I have got it half working now... The problem now seems to be that the debugger stops after a few seconds. So I have no way of verifying that the debugger is actually working.

David Dehghan · Accepted Answer · 2018-03-08 09:30:14Z

0

a couple trouble shooting tips:

1) make sure your debug port is open. run this from your host.

nc -zv test.example.com 30302

2) make sure your webserve does not reload your app automatically. That will break the debugger connection. Put a print or log statement in your code which runs at startup time to make sure your app is not being loaded twice. This is for socketio running on flask. but django and other webservers have something similar.

socketio.run(app, host="0.0.0.0", port=5000, debug=True, use_reloader=False)

answered Mar 8, 2018 at 9:30

David Dehghan

25.3k11 gold badges113 silver badges101 bronze badges

Collectives™ on Stack Overflow

Debug python application running in Docker

Dockerfile

docker-compose.yml

launch.json

The Issue

EDIT: Minor update

Solution

3 Answers 3

2 Comments

Edit Jan 24, 2017

5 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

Dockerfile

docker-compose.yml

launch.json

The Issue

EDIT: Minor update

Solution

3 Answers 3

2 Comments

Edit Jan 24, 2017

5 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related