Azure vs AWS Reliability

The Reliability Gap

Azure has had a rough stretch. Major global outages in 2023, 2024, and 2025 took down core services for hours, sometimes affecting authentication (Entra ID), meaning customers couldn't even log in to assess the damage. The July 2024 CrowdStrike/Azure incident wasn't strictly Azure's fault, but it exposed how deeply coupled many Azure-dependent organizations are to a single failure domain.

AWS has outages too. But the pattern is different: AWS outages tend to be regional and service-scoped. A DynamoDB issue in us-east-1 doesn't take down S3 in eu-west-1. Azure's architecture has more global dependencies (particularly around Entra ID and Azure AD) where a single control plane failure cascades globally.

Architectural Differences

Azure: Resource groups and regions

Azure organizes resources into resource groups within a subscription. Many control plane operations (Azure AD, Management Groups, some Azure Monitor features) are global services. When a global service goes down, everything goes down.

AWS: Regions as independent deployments

AWS regions are designed to be fully independent. Each region has its own IAM control plane, its own service endpoints, and its own data plane. A failure in us-east-1 doesn't propagate to eu-west-1 (with rare exceptions like IAM's global endpoint for some operations).

This architectural choice means:

AWS services fail independently and regionally
Multi-region on AWS gives you genuine isolation
You can build around single-region failures without relying on the provider's global resilience

Availability Zones

Both providers have AZs (physically separated data centers within a region). AWS has been running AZs longer and has more consistent implementation. Each AZ is a real independent failure domain with separate power, cooling, and networking. Azure's AZ implementation is newer and has had growing pains.

Real-World Impact

The question isn't "does the provider go down?" — both do. The question is:

How often? AWS has fewer major incidents per year.
How broadly? AWS failures tend to be regional; Azure's can be global.
How long? AWS typically restores faster (hours, not half-days).
Can you architect around it? Easier on AWS due to regional independence.

What AWS Does Better

Regional isolation: Your us-east-1 stack genuinely doesn't depend on us-west-2 (if designed correctly)
Service-level SLAs: Individual services have their own uptime guarantees you can architect against
Multi-AZ by default: Most managed services (RDS, ElastiCache, ECS) run multi-AZ with a checkbox, not a redesign
Transparent post-mortems: AWS publishes detailed incident reports that help you understand what failed and why

What AWS Doesn't Solve

us-east-1 concentration: Many AWS services have dependencies on us-east-1 (IAM global endpoint, some S3 operations, Route 53). If you're us-east-1-dependent, a major incident there still hurts.
Single-region applications: If you only deploy to one region on AWS, you have the same SPOF as Azure. Just with better odds.
Shared fate with the provider: No matter the cloud, if their control plane is down, you can't deploy or modify resources. The data plane (running workloads) typically continues, but you can't fix things.

Building for Resilience on AWS

The advantage of AWS isn't that it never goes down. It's that the architecture makes it possible to tolerate failures:

Multi-AZ: Survive a data center failure (free for most services, minimal extra cost for others)
Multi-region: Survive a region failure (expensive, complex, but possible with DynamoDB Global Tables, Aurora Global Database, and now Cognito multi-region replication)
Cell-based architecture: Isolate blast radius so one failure only affects a subset of customers
Chaos engineering: Tools like AWS Fault Injection Service let you test resilience before incidents happen

The Migration Argument

If your team is evaluating migration partly because of Azure reliability:

Moving to AWS doesn't guarantee zero downtime. You still need to design for failure
But AWS gives you better building blocks for redundancy
The multi-region story on AWS is more mature and better documented
You gain genuine regional independence that Azure's architecture doesn't fully provide

The teams that get the most out of switching are the ones that don't just move their existing architecture. They redesign for the redundancy model AWS provides.