A Guide to Multi-Region Disaster Recovery

2025-10-20

The Cloud Went Down. Your SaaS Doesn't Have To.

If you're in the tech world, your phone probably lit up today with news of the massive AWS outage. As reported in the news around the world, a failure in the US-EAST-1 region knocked out major services, from Snapchat and Reddit to Ticketmaster and Wealthsimple. For SaaS leaders, this is a recurring nightmare that highlights a critical truth: relying on a single cloud region is not a question of if it will fail, but when.

The cloud providers (AWS, Azure, Google) provide incredible tools, but they do not automatically make your application resilient. That responsibility is ours, the engineers and architects. Today’s outage wasn't a failure of "the cloud"; it was a failure of single-region architectures.

The good news is that building a truly resilient, multi-region SaaS product is not only possible but essential. I know because I’ve done it.

The Single-Region Trap: A Case Study in Risk

At a previous company, Hippo CMMS, I was faced with this exact vulnerability. Our entire SaaS platform was operating as a single process on a single physical machine within our data centers. There was no redundancy. A simple hardware failure, let alone a regional disaster, could have brought the entire product offline for all 800+ of our clients.

This is the "single-region trap." It’s fast, easy, and cheap to deploy everything to one region (like the US-EAST-1 region that failed today), but it creates a massive single point of failure (SPOF).

Our objective was clear: migrate to the cloud and architect a platform with high availability and multi-region failover, all with zero unscheduled downtime for our customers.

The Blueprint for a Multi-Region, Resilient SaaS

We successfully migrated the entire platform to Microsoft Azure in under six months, and the architectural principles we used are a blueprint for avoiding today's exact problem.

Here are the core components of a truly resilient multi-region architecture:

1. Global Traffic Management
This is the "front door" of your application. We used Azure Traffic Manager and Azure Front Door (AWS Route 53 with its health checks is a direct equivalent). This service does two things:

  • Geographic Routing: It sends users to the geographically closest data center for low latency.
  • Automatic Failover: This is the key. The traffic manager constantly runs health checks on all your regions. The moment it detected that our primary US region was unhealthy, it would automatically stop sending traffic there and reroute all users to our healthy Canadian region, with no human intervention required.

This strategy is most effective when you are running your tasks or containers in multiple regions all the time (an "active-active" or "active-passive" setup). If you are already auto-scaling your containers to two or more instances to handle load, you're already prepared for this. Simply deploy your application to a second region, set its default to 1 instance, and allow each region to scale independently. You likely won't see a significant increase in hosting costs, since you were already paying for auto-scaling, and now your API layer is protected from a single-region failure.

2. Replicated & Sharded Databases
Failing over your application servers is easy; failing over your data is the hard part. We moved our backend to Azure SQL Server and implemented a database sharding pattern using Elastic Pools.

  • Why Shard? It allowed us to guarantee data sovereignty (e.g., Canadian data must stay in Canada) while also enabling resilience.
  • How it Works: Each tenant's data was sharded. We used a Redis cache to store and quickly look up the database location for each user. In a failover event, the application servers in the new, healthy region would simply query the Redis cache, get the correct database connection string (which might still be in the original region or a replicated one), and continue operating. For a full DR, you would have geo-replicated database read-replicas that can be promoted to primary.

3. Stateless Application Tiers
Your application servers (running on Managed VMs, container instances, or Kubernetes) should be stateless. This means no user session data is stored on the server itself. All state should be externalized. This allows you to spin up new instances in a new region instantly during a failover without worrying about "losing" user sessions.

Going Deeper: The Circuit Breaker Pattern

A multi-region architecture protects you from a macro failure. But what about micro-failures? What happens when your application in the "healthy" region tries to call a single microservice that is failing? This can lead to a cascading failure that brings down your "healthy" region, too.

This is where the Circuit Breaker pattern is essential.

Think of it like an electrical circuit breaker in your home.

  • Closed State: Everything is normal. Requests from your "Orders" service flow to your "Payments" service.
  • Open State: The "Payments" service fails a few times (e.g., timeouts). The circuit "trips" and opens. For the next 30 seconds, all calls from "Orders" to "Payments" fail instantly. This is crucial: it stops the "Orders" service from locking up and waiting for a timeout, and it gives the "Payments" service time to recover without being hammered by requests.
  • Half-Open State: After the 30-second timeout, the circuit breaker lets one test request through. If it succeeds, the circuit closes. If it fails, the circuit opens again for another 30 seconds.

This pattern prevents a single failing component from creating a domino effect that takes down your entire application. It allows your app to gracefully degrade instead of crashing completely.

Checkout OpenFuse if you want to learn more.

The Cloud Is a Tool, Not a Crutch

Today’s AWS outage is a powerful reminder that the cloud providers give us the components, but we are the architects responsible for resilience.

If your SaaS product is confined to a single region, you are not just at risk—you are operating on borrowed time. Don't wait for the next outage to test your disaster recovery plan. Build for failure, and your application will be the one that stays online when the rest of the internet goes dark.