Migrating to Firebase Gen 2 Cloud Functions

Firebase has recently pushed heavily toward their Gen 2 architecture, built explicitly on top of Google Cloud Run. While Gen 1 functions were strictly tied to App Engine architecture, Gen 2 brings massive advantages in concurrency and cold-start mitigations.

Why Migrate?

1. Massive Concurrency: A single Gen 2 instance can process up to 1,000 concurrent requests. Gen 1 restricted you to 1 request per instance, meaning 1,000 requests caused 1,000 cold starts.
2. Native Cloud Run Integration: You can treat Gen 2 functions directly as Cloud Run containers.
3. Traffic Splitting: Safely rollout an A/B test of backend logic instantly.

The Pain Points of Migration

Be cautious of the runtime environment changes. The firebase-functions/v2 SDK completely restructures how triggers are declared:

typescript
// Gen 1
exports.myFn = functions.https.onRequest((req, res) => { ... });

// Gen 2
import { onRequest } from "firebase-functions/v2/https";
export const myFn = onRequest({ cors: true, maxInstances: 10 }, (req, res) => { ... });

The most common failure during transition is IAM permission errors. Gen 2 uses the default Compute Engine Service Account by default rather than the App Engine one. Check your GCP IAM roles!