debug python code running in docker container from host using vscode

Question

I have a container running on my host with a python process and I have the vs code installed on the host. Is it possible to debug the python process from the host installed vscode? If yes, how can this be achieved?

Answer 1

Since I do not know what python process you have running, I'll use FastAPI as an example.

1. First, you need to define a new configuration in the file <project_root>/.vscode/launch.json . To access this file, you can go to the Run & Debug section on the activity bar, and press the cog/wheel at the top.

Add a new item in the configurations like shown below.

{
    "version": "0.2.0",
    "configurations": [
        {
        "name": "Python: Remote Attach",
        "type": "python",
        "request": "attach",
        "connect": {
            "host": "localhost",
            "port": 5678
        },
        "pathMappings": [
            {
            "localRoot": "${workspaceFolder}",
            "remoteRoot": "."
            }
        ]
        }
    ]
}

2. Now you need to include debugpy . If you are using a requirements file, you can just add it there. If you use Poetry , you can run poetry add debugpy in your terminal (the Dockerfile example shows how you can use Poetry in a docker image).

3. First option - In your Dockerfile you need to run debugpy and make it listen for port 5678 . Now the debugger will start every time you run the container and await attachment.

FROM python:3.10.0

# Set the working directory:
WORKDIR /usr/src

# Copy the pyproject.toml file (or requirements.txt) to cache them in the docker layer:
COPY [ "./src/pyproject.toml", "./"]

# Set the python path if needed.
# For example, if main.py is not located in the project root:
ENV PYTHONPATH="$PYTHONPATH:${PWD}"

# Upgrade pip and install Poetry:
RUN pip install --upgrade pip && pip install poetry==1.1.12

# Project initialization using Poetry:
RUN poetry config virtualenvs.create false \
    && poetry install --no-interaction --no-ansi

# Run the application:
CMD ["python", "-m", "debugpy", "--wait-for-client", "--listen", "0.0.0.0:5678", "-m", "uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000", "--reload", "--reload-exclude", "tests"]

EXPOSE 8000 5678

4. Second option - Set up the debugger in the main.py file by adding the lines below. This means that the debugger will be attached to the container when it starts; if the debugger variable is set to True.

debugger = True

if __name__ == "__main__":
    if debugger:
        import debugpy
        debugpy.listen(("0.0.0.0", 5678))
        debugpy.wait_for_client()

    uvicorn.run(
        "main:app",
        host="localhost",
        port=8000,
        log_level="info",
        reload=True,
    )

5. Both examples need the Dockerfile to expose the port 5678 . Now, after running the container, the debugger will "pause" and await attachment. To attach the debugger, go back to Run & Debug section on the activity bar in VSCode and select Python: Remote Attach from the dropdown menu and press play.

Now you should be able to use the debugger inside the docker container.