At the fintech startup we served financial data to users across Europe, Asia, and the US. Latency mattered because stale stock data is worse than no stock data. We went multi-region not because it was trendy but because a user in Singapore waiting 400ms for a London API response was a user who stopped trusting the product.
That experience taught me something most architecture blogs skip over: multi-region isn’t a scaling decision. It’s a commitment. You’re signing up for a permanent increase in operational surface area, and most teams underestimate what that means on a Tuesday night when replication lag spikes and nobody remembers which region owns writes.
When It Actually Makes Sense
Three situations. That’s it.
Your users are genuinely global and latency affects the product. Not “we have a few customers in Asia.” I mean latency is measurably hurting conversion, trust, or functionality. At the fintech startup, financial data delayed by hundreds of milliseconds was functionally wrong. That’s a real reason.
Compliance requires data residency. GDPR was forcing this conversation for European users. If you must keep EU citizen data in EU, you need a region there. No architecture cleverness gets around legal requirements.
A regional outage is an existential threat. If your product going down for four hours costs more than running a second region for a year, the math works. For most startups I’ve seen – including what we’re building now at Decloud in the EF batch – it doesn’t.
When It Doesn’t
Here is a test I use: if your team doesn’t have 24/7 on-call coverage today, you aren’t ready for multi-region. Full stop.
A second region doesn’t help if nobody is awake to failover when it matters. I’ve watched startups deploy to three regions and then have a single engineer handle incidents at 3am because “the architecture is redundant.” The architecture isn’t the bottleneck. The people are.
Single-region with multiple availability zones handles most failure scenarios. It’s cheaper, the mental model is simpler, and your deploys don’t need a coordination protocol. If you’re a team under twenty engineers, start here and stay here until the pain is specific and measurable.
The Patterns, Briefly
Active-passive is the safe choice. One region handles writes. The other sits warm, ready for failover. You pay for underutilized infrastructure, but your data model stays sane. This is what I would recommend for most teams dipping a toe in.
Active-active is the ambitious choice. Both regions serve traffic and accept writes. Latency improves for everyone. Failover is faster because traffic already flows everywhere. But now you need conflict resolution, and conflict resolution is where engineers go to suffer.
Follow-the-sun is niche. The primary region rotates with time zones. It works for batch workloads and internal tools. I’ve never seen it work well for user-facing products.
Data Will Ruin Your Week
Every multi-region conversation eventually becomes a data conversation. You can handwave traffic routing and load balancing. You can’t handwave “what happens when two regions write to the same row at the same time.”
Classify your data before you do anything else:
- Global and consistent: User accounts, billing state, permissions. This data must be correct everywhere. Synchronous replication or a single write region.
- Regional and isolated: User-generated content tied to geography, local caches. This can live in one region without drama.
- Derived and disposable: Caches, search indexes, computed feeds. Rebuild it if it breaks. Don’t replicate it.
Synchronous replication gives you consistency but adds cross-region latency to every write. Async replication keeps things fast but introduces eventual consistency, which is a polite way of saying “your users might see stale data and you need a plan for that.”
Conflict resolution deserves its own paragraph because it deserves your fear. Last-write-wins sounds simple until you realize your clock synchronization across regions isn’t as tight as you assumed. Application-level merge logic sounds correct until you realize every new feature needs to account for it. CRDTs sound elegant until you realize they only work for specific data structures. Pick your poison. Test it under failure conditions, not just happy paths.
Traffic Routing
Three options, increasing in complexity:
DNS-based routing is cheap and simple. It’s also slow to failover because DNS caching means some users will hit the wrong region for minutes after a switch. Fine for read-heavy traffic. Dangerous if you need fast failover.
Global load balancers give you health checks and faster failover. They cost more and add operational surface. Worth it if your availability targets demand sub-minute recovery.
Application-level routing lets clients or APIs pick a region based on account or data ownership. Maximum flexibility. Maximum chance of a subtle routing bug sending writes to the wrong region.
The Honest Cost
Multi-region costs aren’t just “two of everything.” The infrastructure doubling is the easy part to budget. The hard costs are:
- Cross-region data transfer fees. These add up fast and nobody notices until the bill arrives.
- Doubled deploy pipelines, doubled monitoring, doubled alerting noise.
- On-call engineers who now need to understand two regions and the interactions between them.
- Every new feature ships slower because someone has to ask “does this work multi-region?”
At Google for Startups in Seoul, I watched teams burn runway on infrastructure sophistication that their user base didn’t justify. The startup that nailed single-region reliability shipped faster than the one with a beautiful multi-region setup and a three-person team drowning in operational overhead.
My Actual Advice
If you’re reading this in 2019 and wondering whether to go multi-region: probably don’t. Deploy to a single region with multiple availability zones. Set up proper backups and a disaster recovery plan. Get your deployment pipeline fast enough that you can ship fixes in minutes, not hours.
When the pain becomes specific – real latency complaints from real users in a real geography, a compliance requirement with a real deadline, a post-mortem that shows a regional outage cost real money – then revisit. Start with active-passive. Keep your write path simple. Accept that you’re trading velocity for resilience and make that trade deliberately.
Multi-region isn’t wrong. But it’s almost never urgent, and doing it before you’re ready makes everything else slower.