Step 1 of 9 · Intro

Design a web tier that survives a zone failure

Spread across zones, size for N+1, and know what each failover really does.

How it works

• ›An ALB sends requests only to healthy targets in the zones you enable. Each target is checked every 30 seconds by default and removed after 2 failed checks, so about 60 seconds.
• ›In an RDS Multi-AZ DB instance deployment the one standby supports failover but does not serve reads. In a Multi-AZ DB cluster deployment two standbys can serve reads. Aurora Replicas serve reads and are the failover targets.
• ›Aurora recommends putting replicas in different Availability Zones from the writer.
• ›Limits come from AWS documentation (default quotas in us-east-1). Where AWS publishes no figure, such as how many requests a container or database handles, the lab states its assumption on the component.

What you'll build

1. A zone-aware stack for 4,000 requests a second
2. Capacity that survives losing a task
3. The arithmetic of losing a whole zone
4. A peak design with a cache
5. An empty cache at peak
6. A database that survives its writer failing
7. Failover that applications ride out