I'm building a multi-region API setup and need request routing

Sure — request routing in a multi-region API setup usually comes down to choosing how clients reach a region and how requests are steered across regions safely.

Common routing patterns

1) Global DNS routing

Use a global DNS provider to return the IP/hostname of the nearest or healthiest region.

Pros

• Simple
• Cheap
• Easy to operate

Cons

• DNS caching can make failover slow
• Limited per-request intelligence
• Harder to do fine-grained traffic shaping

Best for

• Basic geo routing
• Active-active setups with tolerant failover requirements

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2) Global load balancer / edge proxy

Put a global traffic manager in front of regional services.

Examples:

• Cloudflare Load Balancer
• AWS Route 53 + Global Accelerator
• Azure Front Door
• GCP Cloud Load Balancing

Pros

• Faster failover
• Health checks
• Can do geo, latency, weighted, and failover routing
• Better control than DNS alone

Cons

• More cost
• More moving parts
• Can introduce an extra hop

Best for

• Production multi-region APIs
• Low-latency or high-availability requirements

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3) Client-side routing

The client or SDK selects the region, often using a region map or service discovery endpoint.

Pros

• Very flexible
• Can optimize based on user/session/business logic

Cons

• More complex clients
• Harder to update
• Not ideal for public APIs without controlled clients

Best for

• Internal services
• Mobile/desktop apps with managed SDKs

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Routing strategies

Latency-based

Route to the region with the lowest estimated latency.

Good when:

• You want speed
• Regions are similar in capability

Watch out for:

• Users getting bounced unexpectedly
• Cross-region data access increasing latency

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Geo-based

Route by user geography.

Good when:

• Data residency matters
• You want users to stay in a nearby region

Watch out for:

• Geography does not always equal lowest latency
• Border cases can be inconsistent

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Weighted

Send some percentage of traffic to each region.

Good when:

• Gradual rollouts
• Canarying a new region
• Load balancing uneven capacity

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Failover / active-passive

Primary region handles traffic until it fails, then secondary takes over.

Good when:

• Simplicity matters
• Strong consistency or simpler data architecture is needed

Downside:

• Secondary capacity may sit idle
• Failover can still be tricky if data is not replicated properly

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Active-active

Multiple regions serve traffic simultaneously.

Good when:

• You need higher availability
• You want lower latency globally

Watch out for:

• Data consistency
• Session affinity
• Conflict resolution
• Operational complexity

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Key design concerns

1) Session and state handling

If requests can move between regions, avoid region-local session state unless you have:

• Stateless auth tokens
• Shared session store
• Sticky routing

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2) Data locality

If your API reads/writes a database, route users to the region where their data lives when possible.

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3) Health checks

Use:

• Liveness checks for instance health
• Readiness checks for regional readiness
• Synthetic checks from multiple geographies if possible

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4) Failover behavior

Decide:

• Automatic or manual failover?
• How fast should it happen?
• What happens to in-flight requests?
• Do you retry at the edge or client?

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5) Idempotency

If requests might be retried across regions, ensure:

• POST/PUT operations are idempotent where possible
• Idempotency keys are supported for writes

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Practical recommendation

For most multi-region APIs, a strong default is:

• Global load balancer or edge proxy
• Latency-based routing
• Health checks with automatic failover
• Stateless API tier
• Region-aware data strategy
• Weighted routing for gradual cutovers

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Simple architecture example

Client
  -> Global edge / load balancer
    -> Region A API
    -> Region B API
    -> Region C API

Routing decision based on:

1. Geo/latency
2. Regional health
3. Weighted policy
4. Failover if unhealthy

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If you want, I can also help you design:

1. a routing architecture for AWS/Azure/GCP,
2. a failover strategy,
3. or a routing decision flowchart for your API.