Скачать или смотреть How to Run FastAPI App and TCP Server as Async Tasks in the Same Event Loop

Learn how to efficiently run a FastAPI application alongside a TCP server using asynchronous tasks, enabling seamless communication between different instances.
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Running a FastAPI App and TCP Server as Async Tasks in the Same Event Loop

When building applications that require both HTTP and TCP communication, developers face the challenge of running these servers concurrently without blocking each other. This issue becomes even more complex when it involves handling multiple ports and ensuring that communication is smooth and effective between different client instances. In this guide, we will explore how to run a FastAPI application alongside a TCP server using asynchronous tasks within the same event loop.

Understanding the Challenge

Imagine you have a setup where:

Client 1 connects to a TCP server running on a different instance on ports 8001, 8002, and 8003.

The server is responsible for relaying raw data from the TCP socket to a websocket client connected on the FastAPI port (8000).

You are able to establish a TCP connection but encounter issues when trying to listen for incoming TCP traffic on those additional ports.

In the original implementation, the TCP server does not seem to get activated, resulting in failed socket connections. This is likely due to the way asynchronous tasks are being launched and handled in FastAPI.

Solution Overview

To address the problem, you need to ensure that the TCP servers start before the yield statement in the lifespan event handler. This ensures that they are active while the FastAPI application is running. Below is a structured approach to achieve this.

Step 1: Modify the Lifespan Event

Change your startup_event function to initialize and start the TCP servers properly. Here's how to do it:

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

Step 2: Implement TCP Server Creation Logic

Ensure that the TCP server logic can handle incoming data efficiently. Here's a skeleton for the start_tcp_server function:

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

Step 3: Ensure Proper Shutdown Logic

While it’s crucial to start the TCP servers effectively, proper shutdown procedures must also be in place to avoid abrupt terminations. Optionally implement a stopping mechanism for each TCP server.

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

Full Implementation

Integrating all these changes, your main FastAPI application would look something like this:

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

Conclusion

By adjusting the server startup sequence and ensuring proper event handling, it's possible to run a FastAPI app and multiple TCP servers seamlessly within the same event loop. This architecture not only streamlines communication between clients but also enhances the scalability and responsiveness of your application. Happy coding!