Regions and availability zones

AWS regions and availability zones

AWS has data centers all over the world, grouped into regions and availability zones. An AWS region is a separate geographic area, such as us-east-2 (Ohio), eu-west-1 (Ireland), and ap-southeast-2 (Sydney). Within each region, there are multiple data centers known as availability zones, such as us-east-2a, us-east-2b, and so on.

Each availability zone in the same region is isolated, but connected via low-latency links, so AWS makes it easy to deploy your infrastructure across multiple availability zones as if it was all in one big data center, such as running a cluster of EC2 instances, with the instances distributed across us-east-2a, us-east-2b, and us-east-2c. This makes your infrastructure resilient to the outage of an entire data center.

If you want to be resilient to the outage of an entire region (e.g., all data centers in us-east-2 going down), you can deploy your infrastructure across multiple regions, but this tends to be more difficult. Latency between regions is significantly higher, and as AWS treats regions completely independently, there isn’t much tooling for multi-region deployments built-in. You’ll need to replicate your infrastructure and data and solve multi-region latency and eventual consistency issues: check out Architecting Multi-Region SaaS Solutions on AWS and How to build a multi-region active-active architecture on AWS as starting points.