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  "description": "An availability zone (AZ) is an isolated data centre within a cloud region. AZs in the same region share low-latency private network links but use physically separate buildings, power, cooling, and uplinks, so a fault in one AZ does not propagate to the others. AZs are the cloud's unit of fault isolation below the region level.\n\n\nWhy multi-AZ matters\n\n * Hardware failures. A single AZ can lose power, network, or cooling. Workloads spanning multiple AZs survive.\n * Software upgrades. Provider rol",
  "path": "/engineering-glossary/availability-zone-cloud-failure-domain/",
  "publishedAt": "2026-05-12T18:49:33.000Z",
  "site": "https://sahilkapoor.com",
  "tags": [
    "AWS",
    "Region",
    "Cloud Computing",
    "Kubernetes"
  ],
  "textContent": "**An availability zone (AZ)** is an isolated data centre within a cloud region. AZs in the same region share low-latency private network links but use physically separate buildings, power, cooling, and uplinks, so a fault in one AZ does not propagate to the others. AZs are the cloud's unit of fault isolation below the region level.\n\n## Why multi-AZ matters\n\n  * **Hardware failures.** A single AZ can lose power, network, or cooling. Workloads spanning multiple AZs survive.\n  * **Software upgrades.** Provider rollouts often happen one AZ at a time; multi-AZ deployments stay available during these.\n  * **SLA tiers.** Many managed services only offer their stronger SLA when configured multi-AZ.\n\n\n\n## Common multi-AZ patterns\n\n  * **Load-balanced stateless services.** Run replicas across AZs behind a load balancer; if one AZ fails, traffic routes to the others.\n  * **Multi-AZ databases.** RDS Multi-AZ, Aurora, MongoDB Atlas replica sets, ElastiCache replication groups.\n  * **AZ-aware Kubernetes.** Pod topology spread constraints place replicas in different AZs.\n\n\n\n## Cost considerations\n\nInter-AZ traffic in AWS is billed per GB in each direction (about USD 0.01 per GB in 2026). Chatty multi-AZ deployments can produce surprising data-transfer bills; chatty internal traffic is often the largest hidden cost in AWS architectures.\n\n🔗\n\n**Related Terms**\nAWS, Region, Cloud Computing, Kubernetes.",
  "title": "Availability Zone",
  "updatedAt": "2026-05-13T19:14:27.530Z"
}