Designing systems that are both highly available and cost-efficient is a core challenge in AWS architecture. You want your applications to be resilient to failures, but you also need to avoid unnecessary spending. The key principles for achieving this balance are: using multiple Availability Zones (multi-AZ), minimizing overprovisioning, and designing for effective failover.

Balancing redundancy and cost always involves trade-offs. More redundancy—such as running extra standby servers or using multi-region deployments—increases availability but also raises costs. To optimize, you need to assess your application's tolerance for downtime and degraded performance. For many workloads, a single standby instance per AZ is sufficient, especially if auto scaling can quickly add capacity after a failure. Using managed services like RDS Multi-AZ or DynamoDB global tables can provide resilience with less operational overhead, but always review the cost implications of each option.

Right-sizing your resources and leveraging automation are essential:

• Avoid overprovisioning by monitoring usage patterns and scaling only when needed;
• Remember that the most cost-effective high availability comes from smart architecture choices, not simply adding more infrastructure.