How would you design a highly available web application across multiple AZs?
AWS · Advanced level
Answer
For a highly available web app, I deploy across multiple AZs with ALB, private app subnets, autoscaling compute, managed multi-AZ data services, monitoring, backups, and safe deployment/rollback patterns.
Technical explanation
High availability needs multiple AZs, health checks, autoscaling, resilient data services, and tested failure behavior.
Availability design should start from business impact, RTO/RPO, dependency mapping, and failure-mode testing, not only from deploying resources in multiple AZs.
Stateless compute, resilient data stores, health checks, rollback, backups, and game days are all required to prove resilience.
Lower recovery targets require higher cost, more automation, replicated data, pre-provisioned capacity, and regularly tested runbooks.
Hands-on example
1. Draw the workload dependency map, then define target RTO/RPO with the business owner.
2. Implement multi-AZ or multi-Region components required by those targets, including data replication and automated provisioning.
3. Run a game day: instance failure, AZ impairment, database failover, restore test, or regional failover depending on scope.
4. Measure actual recovery time/data loss and update the architecture or runbook if targets are missed.
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