How do I route API traffic between regions?

Routing API traffic between regions usually means choosing which regional endpoint a client should call, and how to fail over if a region is unhealthy. The best approach depends on whether you want:

• Latency-based routing: send users to the closest/fastest region
• Active-active: serve traffic from multiple regions at once
• Active-passive: one primary region, another stands by
• Failover only: route to a backup region if the primary fails

Common patterns

1) DNS-based routing

Use a global DNS provider or cloud DNS feature to return different regional IPs/endpoints based on:

• geographic location
• health checks
• latency

Examples:

• AWS Route 53 latency-based routing + health checks
• Azure Traffic Manager
• Google Cloud Load Balancing with global routing
• Cloudflare Load Balancer

Pros

• Simple
• Works well for public APIs

Cons

• DNS caching can delay failover
• Not ideal for very fast switchover

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2) Global load balancer / API gateway

Put a global load balancer in front of regional API deployments. It routes requests to the nearest or healthiest region.

Examples:

• AWS Global Accelerator
• Google Cloud External HTTP(S) Load Balancer
• Azure Front Door
• Cloudflare Load Balancer / CDN edge routing

Pros

• Faster failover than DNS
• Better observability and traffic control
• Can route at L7 using path/host/header rules

Cons

• More infrastructure cost
• More configuration complexity

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3) Client-side routing

The client app decides which region to call, based on:

• user locale
• stored preferences
• health endpoint response
• custom routing logic

Pros

• Maximum control
• Useful for internal services or mobile apps

Cons

• Harder to manage
• Requires client updates
• Weak for failover if clients are not well-behaved

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4) Service mesh / internal routing

For service-to-service traffic across regions, use:

• Istio
• Linkerd
• Consul
• Envoy-based global service discovery

Pros

• Great for microservices
• Can do retries, circuit breaking, locality-based routing

Cons

• Overkill for simple public APIs

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Recommended setup for most APIs

A common architecture is:

1. Deploy the API in each region
2. Use a global entry point (DNS or global load balancer)
3. Expose a health check endpoint per region
4. Replicate shared data or use a multi-region database strategy
5. Add failover rules and optionally latency-based routing

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Things to watch out for

Data consistency

If your API is stateful, routing is not enough. You also need:

• multi-region database replication
• sticky sessions or stateless design
• conflict resolution for writes

Session handling

Avoid server-local sessions if traffic can move regions. Prefer:

• JWTs
• centralized session store
• stateless auth

Latency and retries

Make sure clients and gateways:

• use reasonable timeouts
• retry only safe requests
• avoid retry storms during outages

DNS TTL

If using DNS, keep TTL low enough to allow changes, but not so low that resolution becomes expensive.

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Example decision guide

• Public API, simple failover → DNS-based routing
• Public API, fast failover/global performance → global load balancer
• Internal microservices → service mesh
• Mobile/web client controls region → client-side selection

If you want, I can also show:

• an AWS-specific design
• an Azure/GCP design
• a Cloudflare-based setup
• or a reference architecture diagram for multi-region API routing.