What you need to know about Startup and Shutdown Events in FastAPI and ASGI Applications

When building FastAPI and ASGI applications, it’s important to understand the concepts of startup and shutdown events. These events allow you to perform actions before the application starts and after it shuts down, respectively.

Startup Events

Startup events are triggered when the application is initialized. This is where you can perform tasks like setting up database connections, initializing caches, or loading configuration settings. In FastAPI, you can define startup event handlers using the app.on_event("startup") decorator.

from fastapi import FastAPI

app = FastAPI()

@app.on_event("startup")
async def startup_event():
    # Perform startup tasks here

Shutdown Events

Shutdown events are triggered when the application is shutting down. This is where you can perform tasks like closing database connections, cleaning up resources, or saving application state. In FastAPI, you can define shutdown event handlers using the app.on_event("shutdown") decorator.

@app.on_event("shutdown")
async def shutdown_event():
    # Perform shutdown tasks here

Order of Execution

It’s important to note that startup events are executed in the order they are defined, while shutdown events are executed in the reverse order. This means that if you have multiple event handlers, you can control the order in which they are executed by defining them accordingly.

Conclusion

Understanding startup and shutdown events in FastAPI and ASGI applications is crucial for ensuring that your application starts and stops gracefully. By utilizing these event handlers, you can perform necessary setup and cleanup tasks to ensure that your application runs smoothly.