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Asked: 2024-09-27T12:26:52+05:30 In:

I am trying to implement logging for my FastAPI endpoints that are deployed in a Docker container. However, I’m not seeing any log output in my console or logs. How can I set up Python logging in a way that it correctly captures log messages from my FastAPI application running in Docker? Any suggestions or guidance on this would be greatly appreciated.

I’ve been working on a FastAPI project that I’ve containerized with Docker, and I’m encountering a major issue with logging. I’ve been trying to implement logging for my endpoints so I can keep track of requests and errors, but I’m just not getting any log output in my console or logs after deploying the container. It’s really frustrating because I need this information to debug some API issues.

Here’s what I’ve done so far: I set up a logging configuration in my FastAPI app using Python’s built-in logging module. The intention was to capture both info and error level logs. In my Dockerfile, I made sure to expose the correct port and run the FastAPI application using `uvicorn`. I also set the `–host` and `–port` options, but when I look at the container logs, it’s like my logging settings are completely ignored.

I’ve checked the basic things, like ensuring that my logging configuration is actually being invoked when the app starts, and I’ve made sure to set the logging level to DEBUG to get more visibility. But still, nothing! I’ve also looked into redirecting logs to stdout, since Docker captures stdout and stderr, but I’m not sure if I’m doing that part correctly.

Has anyone faced a similar issue? Or does anyone have a working example of setting up logging in a FastAPI application deployed in Docker? I’m really keen to know if there’s a specific way to set up the logging configuration to work seamlessly within a Docker environment. Is there something I might be missing in the setup, or could it be a Docker-specific issue? Any insights or sample code snippets would be super helpful. Thanks in advance for any help!

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    2 Answers

    1. Logging Issues in FastAPI with Docker

      It sounds like you’re dealing with a frustrating situation! I’ve been there too. Setting up logging can be tricky, especially when you’re trying to make it work within a Docker container. Here are a few things you might want to check:

      1. Logging Configuration

      Make sure your logging configuration is set to log to stdout. In your FastAPI app, you can configure logging like this:

      import logging
from fastapi import FastAPI

app = FastAPI()

logging.basicConfig(
    level=logging.DEBUG,
    format="%(asctime)s - %(name)s - %(levelname)s - %(message)s"

      This ensures your logs get printed correctly. The `format` helps you see more details.

      2. Dockerfile Configuration

      In your Dockerfile, ensure you’re using the right commands to run your FastAPI app. A simple example could look like this:

      FROM python:3.9
WORKDIR /app
COPY . .
RUN pip install -r requirements.txt
CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000"]

      This `CMD` command runs the FastAPI app, and it should also carry over logging output to Docker logs.

      3. Check Docker Logs

      After you run your container, use `docker logs ` to see the logs. Don’t forget that if your container is crashing, it might not have a chance to log anything.

      4. Ensure Proper Exception Handling

      Make sure that you’re catching exceptions in your endpoints and logging them. You can use FastAPI’s exception handlers for that:

      from fastapi import HTTPException

@app.get("/items/{item_id}")
async def read_item(item_id: int):
    if item_id < 0:
        logging.error("Negative item ID queried!")
        raise HTTPException(status_code=400, detail="Item ID must be a positive integer")
    return {"item_id": item_id}

      5. Docker Compose or Kubernetes

      If you're using Docker Compose or Kubernetes, make sure you're not routing logs somewhere unexpected. Sometimes, services can override or redirect logging in unexpected ways.

      6. Debugging Tips

      If nothing seems to work, consider running your FastAPI app outside Docker to see if the logging works there. This can help you figure out if it's a Docker issue or something with the app itself.

      Hope this helps you troubleshoot the issue, and you get those logs working soon!

    2. It seems that you’re facing a common issue related to logging when containerizing a FastAPI application with Docker. To ensure that your logging configuration is functional and outputs to the console correctly, double-check your setup to make sure logs are directed to stdout. FastAPI, when run with Uvicorn, has its default logging configured to emit logs to stderr. You might want to customize your logging setup using the built-in `logging` module to explicitly direct logs to stdout. For instance, you can set up a stream handler like this:

      import logging
import sys

logging.basicConfig(
    level=logging.DEBUG,
    format="%(asctime)s - %(name)s - %(levelname)s - %(message)s",
    handlers=[logging.StreamHandler(sys.stdout)]
)

      This ensures that your logs are visible in the Docker logs. Additionally, make sure that you are using the correct log levels in your application code; for example, using `logger.info()` and `logger.error()` statements at appropriate places to capture normal operation and errors. Lastly, verify your Docker run command and settings. If you need to see logs directly, use the command docker logs -f your_container_name to tail the logs. If everything is set up as described but still not outputting logs, it may help to run your FastAPI application outside of Docker to isolate the issue to either your app or Docker environmental settings.

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