How to Fix uvicorn Suppressing Python's Syslog for gelf Driver in Your FastAPI Application

Discover how to solve the issue of `uvicorn` not logging Python's syslog messages to your `gelf` logging instance in FastAPI.
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This video is based on the question https://stackoverflow.com/q/65428781/ asked by the user 'programmar' ( https://stackoverflow.com/u/8126904/ ) and on the answer https://stackoverflow.com/a/65479547/ provided by the user 'programmar' ( https://stackoverflow.com/u/8126904/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Issue: Uvicorn Suppressing Python's Syslog Messages

If you are running a FastAPI application using the uvicorn web server within a Docker container and are trying to log messages via Python's syslog, you might encounter a problem where those syslog messages are not appearing in your logging instance via the gelf driver. Instead, you only see the default uvicorn logging messages. This can be frustrating, especially if your application relies on syslog for logging critical information.

The Setup: FastAPI and Uvicorn with Docker

In your setup, you have:

A Docker container running Ubuntu 18 with rsyslog as a logging service.

A FastAPI application powered by the uvicorn web server.

The application is successfully logging messages to the logging instance using the gelf driver.

You've noticed that while uvicorn logs appear in your logging instance, syslog messages sent via Python’s syslog module do not.

Here's an example of the code you might be using for logging in your FastAPI app:

[[See Video to Reveal this Text or Code Snippet]]

Despite this setup working correctly within the container (as confirmed by rsyslog’s log files), the gelf logging instance fails to capture the syslog messages.

Why Is This Happening?

The core of the problem lies with gelf ignoring syslog messages, which usually happens due to the way gelf interfaces with log sources. Essentially:

When uvicorn manages the logging, it might be configured in a way that bypasses your syslog settings.

Though syslog messages are being recorded correctly in rsyslog, they do not seem to make the journey to the gelf logging instance.

The Solution: Create a Custom Logging Function

To overcome these limitations and ensure that your desired logs are sent to gelf, you can build your own logging function. This function can both log to syslog and print messages to standard output to ensure that everything is captured correctly.

Step-by-Step Solution

Define a Custom Logging Function:
Create a function that logs messages to both syslog and prints them to the console.

[[See Video to Reveal this Text or Code Snippet]]

Replace Syslog Calls with Your Custom Logger:
Update your FastAPI application to use this custom logging function.

[[See Video to Reveal this Text or Code Snippet]]

Test the Integration:
Run your FastAPI application again and check your gelf logging instance to verify that both syslog messages and standard output are now being captured.

Conclusion

By utilizing a custom logging function that incorporates both syslog and print statements, you can resolve the issue of uvicorn suppressing Python's syslog messages when using the gelf driver. This solution ensures that you retain the advantages of using syslog for structured logging while also ensuring visibility within your logging infrastructure.

If you encounter further issues or errors, consider checking your Docker and rsyslog configurations for any additional settings that may affect logging visibility. Happy coding!