AWS Interview Questions
29 AWS questions from real DevOps and cloud interviews, sorted by seniority: IAM, VPC networking, EC2 and scaling, S3 durability, ECS, EKS and Lambda.
What is the difference between a Region and an Availability Zone?
A Region is a geographic location with its own isolated set of infrastructure. An Availability Zone is one or more discrete data centres inside a Region, with independent power, cooling and networking.
| Region | Availability Zone | |
|---|---|---|
| Scope | A geography, such as eu-west-1 | A failure domain inside one, such as eu-west-1a |
| Isolation | Almost total. Most services do not replicate across Regions by default | Independent power, cooling and network |
| Latency between | Tens to hundreds of milliseconds | Single-digit milliseconds |
| Used for | Data residency, disaster recovery | High availability within a Region |
The consequence worth stating: spreading across AZs is how you survive a data centre failure and it is cheap, whereas spreading across Regions is how you survive a Region failure and it is expensive and complicated. Most designs should do the first and very few need the second.
One detail that catches people out: AZ names are mapped per account, so eu-west-1a in your account is not necessarily the same physical zone as in someone else's.