Aframp Backend

Rust/Axum backend for the Aframp platform — multi-region, edge-cached, globally distributed.

---

Global Edge-Caching & Read-Only Replicas (Issue #348)

Architecture Overview

Client
  │
  ▼
CloudFront (edge PoP — <30 ms for /public/*)
  │
  ▼
Route 53 Latency Routing  ──►  us-east-1 ALB  ──►  Primary DB (RW)
                           ──►  eu-west-1 ALB  ──►  Read Replica
                           ──►  ap-southeast-1 ALB ► Read Replica

• CloudFront caches /public/* at the edge (TTL 5 min, stale-while-revalidate 60 s).
• Route 53 latency routing directs each client to the nearest regional ALB.
• Each regional gateway detects its region via the REGION env var and connects to the local read replica for eventual-consistency reads.
• Strong-consistency requests are routed to the primary (us-east-1) via the X-Consistency: strong header.

---

Eventual vs Strong Consistency — Endpoint Mapping

Path prefix	Consistency	Cache policy	DB target	Notes
/public/*	Eventual	public, max-age=300, stale-while-revalidate=60	Read replica	Exchange rates, fee schedules, public docs
/api/v1/rates	Eventual	public, max-age=300, stale-while-revalidate=60	Read replica	Rate feed — tolerates 5 min staleness
/api/v1/fees	Eventual	public, max-age=300, stale-while-revalidate=60	Read replica	Fee structures
/account/*	Strong	no-store, private	Primary	Balances, profile, KYC status
/api/v1/onramp/*	Strong	no-store, private	Primary	Payment initiation
/api/v1/offramp/*	Strong	no-store, private	Primary	Redemption / withdrawal
/api/v1/mint/*	Strong	no-store, private	Primary	Token minting
/api/v1/transaction*	Strong	no-store, private	Primary	Transaction history writes
/api/v1/transfer*	Strong	no-store, private	Primary	Transfers
/api/v1/redemption*	Strong	no-store, private	Primary	Redemption flow
/health/edge	N/A	no-store	Primary (lag check)	DNS failover probe

Forcing Strong Consistency

Any endpoint can be forced to the primary by sending:

X-Consistency: strong

The gateway will:

1. Set X-Route-Primary: true on the response (read by the load balancer).
2. Select DATABASE_URL (primary) instead of DATABASE_READ_REPLICA_URL.

Consistency Header Flow

Request  ──► Gateway middleware (edge_cache.rs)
              │
              ├─ X-Consistency: strong?
              │     YES → X-Route-Primary: true, use DATABASE_URL
              │     NO  → use DATABASE_READ_REPLICA_URL (if available)
              │
              └─ Path-based Cache-Control injected on response

---

Health & Failover

GET /health/edge — used by Route 53 health checks.

Condition	HTTP	DNS action
All dependencies healthy, lag ≤ 5 s	200 OK	No action
Replication lag > 5 s	503	Route 53 fails over to next region
Any dependency down	503	Route 53 fails over to next region

Response body example:

{ "status": "healthy", "region": "eu-west-1", "replication_lag_secs": 0 }

---

Infrastructure

File	Purpose
infra/terraform/edge.tf	CloudFront distribution + path-based cache policies
infra/terraform/global_lb.tf	Route 53 latency routing + health checks

Required Environment Variables (per region)

Variable	Description
REGION	AWS region this instance runs in (e.g. eu-west-1)
DATABASE_URL	Primary PostgreSQL URL (us-east-1)
DATABASE_READ_REPLICA_URL	Local read replica URL

---

Latency Verification

# Run against staging
BASE_URL=https://staging-api.aframp.io ./dist-test.sh

# Run against production with regional IP overrides
US_EAST_1_IP=1.2.3.4 EU_WEST_1_IP=5.6.7.8 AP_SOUTHEAST_1_IP=9.10.11.12 \
  ./dist-test.sh https://api.aframp.io

Target: < 30 ms average for /public/* endpoints (cache hit at CloudFront PoP).