Availability Zone Counts by Region — AWS vs Azure vs GCP

Availability Zone Architecture Comparison

Availability Zones (AZs) are the fundamental building blocks of cloud resilience. Each AZ is an isolated group of one or more data centers with redundant power, networking, and cooling.

AZ Count Summary

Provider	Min AZs	Max AZs	Most Common
AWS	3	6	3
Azure	3	3	3
GCP	3	4	3

AWS Availability Zones

AWS was the pioneer of the AZ concept. Key facts:

• us-east-1 has 6 AZs — the most of any region across all providers
• ap-northeast-1 (Tokyo) and ap-northeast-2 (Seoul) have 4 AZs each
• Most other regions have 3 AZs
• AZs are named with letters (e.g., us-east-1a, us-east-1b)
• AZ naming is per-account — us-east-1a in one account may map to a different physical AZ than in another account

Azure Availability Zones

Azure adopted AZs later but has standardized on 3 per region:

• All regions with AZs have exactly 3
• AZs are numbered 1, 2, 3
• Not all Azure regions have AZs — some older regions use "availability sets" instead
• Azure is expanding AZ support to all regions progressively

GCP Availability Zones

GCP calls them simply "zones":

• us-central1 has 4 zones — the most of any GCP region
• Most regions have 3 zones
• Zones are named with letters (e.g., us-central1-a, us-central1-b)
• Zone naming is consistent across all accounts (unlike AWS)

Architecture Implications

AZ Count	Recommended Pattern
3 AZs	Active-active across all 3, tolerates 1 AZ failure
4 AZs	Active in 3, warm standby in 4th, extra headroom
6 AZs	Spread across all 6 for maximum fault isolation