How do you add caching to FastAPI endpoints to improve performance?

FastAPI has no built-in cache, but several patterns work well: in-process caching with functools.lru_cache / cachetools, Redis-backed caching with fastapi-cache2, and HTTP caching headers for client-side caching.

# Option 1: In-process LRU cache for slow dependencies
from functools import lru_cache
from fastapi import FastAPI, Depends
from typing import Annotated

app = FastAPI()

@lru_cache(maxsize=128)
def get_config_from_db(key: str) -> str:
    # Called once per unique key, then cached in memory
    return f"value_for_{key}"

@app.get("/config/{key}")
def get_config(key: str):
    return {"value": get_config_from_db(key)}

# Option 2: Redis cache with fastapi-cache2
# pip install fastapi-cache2[redis]
from fastapi_cache import FastAPICache
from fastapi_cache.backends.redis import RedisBackend
from fastapi_cache.decorator import cache
from redis import asyncio as aioredis
from contextlib import asynccontextmanager

@asynccontextmanager
async def lifespan(app: FastAPI):
    redis = aioredis.from_url("redis://localhost")
    FastAPICache.init(RedisBackend(redis), prefix="myapp-cache")
    yield

app = FastAPI(lifespan=lifespan)

@app.get("/expensive")
@cache(expire=60)  # cache for 60 seconds in Redis
async def expensive_operation():
    import asyncio
    await asyncio.sleep(2)  # simulate slow DB query
    return {"result": "computed"}

# Option 3: HTTP Cache-Control headers
from fastapi.responses import Response

@app.get("/public-data")
def public_data(response: Response):
    response.headers["Cache-Control"] = "public, max-age=3600"
    return {"data": "cacheable by CDN and browsers"}

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