Fallback for Postgresql DB in AsyncSession in Python

Question

I am currently having two Postgresql Clusters attached to my Python FastAPI server

from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine
from sqlalchemy.orm import sessionmaker

primary_engine = create_async_engine("PRIMARY_DATABASE_URL", echo=False, future=True)
replica_engine = create_async_engine("REPLICA_DATABASE_URL", echo=False, future=True)


async def get_primary_session() -> AsyncSession:
    async_session = sessionmaker(primary_engine, class_=AsyncSession, expire_on_commit=False)
    async with async_session() as session:
        yield session

async def get_replica_session() -> AsyncSession:
    async_session = sessionmaker(replica_engine, class_=AsyncSession, expire_on_commit=False)
    async with async_session() as session:
        yield session

Now assume, that the replica crashes. What would be the best strategy to redirect the traffic back to the primary?

I currently have tried this:

async def get_replica_session() -> AsyncSession:
    try:
        async_session = sessionmaker(replica_engine, class_=AsyncSession, expire_on_commit=False)
        async with async_session() as session:
            yield session
    except:
        async_session = sessionmaker(primary_engine, class_=AsyncSession, expire_on_commit=False)
        async with async_session() as session:
            yield session

However, it used to throw Runtime errors? Hence, it would be great if you could give me some thoughts about it.

Fallback for Postgresql DB in AsyncSession in Python

0 Answers0