3.2.3.11. Configuring Health Checks (Route 53, ALB)

First Principle: Actively monitoring the operational status of application endpoints ensures that traffic is only directed to healthy resources, preventing requests from reaching failing components and maintaining a seamless user experience.

Resilience in distributed systems demands continuous vigilance over component health. Health checks embody this, which is fundamental to achieving high availability and fault-tolerant traffic management.

• Amazon Route 53 Health Checks (Amazon Route 53 health checks monitor the health of various endpoints.) Includes IP addresses, domain names, or even the status of other Route 53 health checks. When an endpoint becomes unhealthy, Route 53 can automatically update DNS records based on configured routing policies (e.g., failover, latency-based, weighted). This is practically relevant for enabling automatic failover to a disaster recovery site or distributing traffic only among healthy instances globally.
• Elastic Load Balancing (ALB) Health Checks (ALB Target Groups perform automated health checks on registered targets.) Includes EC2 instances, containers) using specified protocols (HTTP, HTTPS, TCP). If a target fails a configured number of checks, ALB automatically takes it out of rotation, preventing new requests from being sent to it. This ensures that traffic within a region is always directed to healthy application instances, significantly improving application reliability.

Key Health Check Types:

• Route 53 Health Checks: Monitor endpoints (IPs, domains), update DNS for global routing/failover.
• ALB Health Checks: Monitor targets in Target Groups, remove unhealthy from load balancer rotation.

Scenario: A DevOps team manages a critical global web application. They need to ensure that local application instances are healthy before receiving traffic from an ALB, and that if an entire regional deployment becomes unhealthy, global DNS routes users away from that region.

Reflection Question: How would you configure ALB Target Group health checks and Amazon Route 53 health checks to actively monitor the operational status of application endpoints, ensuring traffic is only directed to healthy resources at both the local (within region) and global levels?

By configuring robust health checks in both Route 53 and ALB, you establish a multi-layered defense against service disruptions, ensuring continuous application availability and a superior user experience.

💡 Tip: When configuring health checks, consider the impact of your chosen interval and unhealthy threshold. Shorter intervals and lower thresholds detect issues faster but can lead to "flapping" if endpoints are intermittently unstable. Longer settings reduce flapping but increase detection time.