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ADR 0004: Deploy All Cloud Functions to europe-west1

  • Status: ✅ Accepted
  • Date: 2025-08-20
  • Deciders: Akshay
  • Tags: infrastructure, region

Context​

Firebase Cloud Functions default to us-central1. We need to pick a region for:

  • Latency to primary user base
  • Colocation with Firestore / Storage
  • Regulatory / data-residency fit
  • Cost parity

At the time of decision, the primary user base is in Europe (UK + Mainland), and the Firebase project was provisioned with a multi-region bucket in eur3 (Europe).

Options Considered​

A. us-central1 (default)​

  • Pros: Default; lowest latency to GCP control plane; widest feature set
  • Cons: 100-200ms RTT from Europe; data crosses Atlantic on every call

B. europe-west1 (Belgium)​

  • Pros: Low latency to UK/EU users; colocated with Firebase eur3 storage; same GCP price class as us-central1
  • Cons: Slightly fewer preview features land first; some 3rd-party services have US-only endpoints

C. europe-west2 (London)​

  • Pros: Closest to UK users
  • Cons: ~10% more expensive; no Firebase-specific advantage over west1

D. asia-south1​

  • Pros: Low latency to India-based contributors
  • Cons: Not where users are; further from Firestore eur3

Decision​

Deploy all Cloud Functions to europe-west1. Codified as REGION = "europe-west1" in shared/config.ts so it's imported by every function.

Consequences​

Positive​

  • Low user-perceived latency on callable functions (~30-60ms from UK)
  • Colocated with storage → no cross-region egress on Storage triggers
  • One region = one source of truth

Negative​

  • Client code must specify the region explicitly, or calls silently route to us-central1 and fail. This is an ongoing footgun:

    // ✅ Correct
    FirebaseFunctions.instanceFor(region: 'europe-west1');

    // ❌ Silent failure
    FirebaseFunctions.instance;

  • Documented prominently in Troubleshooting and Frontend Overview

  • Preview Firebase features sometimes launch in us-central1 first and are unavailable to us for weeks

Neutral​

  • Flutter uses FirebaseFunctions.instanceFor(region: 'europe-west1'); the admin web app uses getFunctions(app, 'europe-west1').
  • When running the emulator, the region is ignored — tests work regardless

Follow-up Actions​

  • Centralize REGION constant in shared/config.ts
  • Document in every relevant doc page (overview, troubleshooting, frontend, deployment)
  • Verify every current Flutter Functions client specifies europe-west1
  • Verify the admin Functions client specifies europe-west1
  • Consider a single Flutter wrapper if the number of direct clients grows

References​