Lifespan event error FastAPI

Why This Happens

In FastAPI, an error occurred during startup or shutdown events. This is one of the most common FastAPI errors developers encounter. Understanding the root cause helps you fix it quickly and prevent it from recurring.

The Problem

@app.on_event('startup')
async def startup():
    raise Exception('DB down')

The Fix

@app.on_event('startup')
async def startup():
    try:
        await init_db()
    except Exception as e:
        logger.error(f'Startup failed: {e}')

Step-by-Step Fix

1. 1

   Identify the error

   Look at the error message: lifespan event error. This tells you exactly what went wrong.

2. 2

   Find the cause

   Check the stack trace to find which line of your FastAPI code triggered this error.

3. 3

   Apply the fix

   Use the corrected code pattern shown above. Test to confirm the error is resolved.