Automated Failover Mechanics

Hope is not a strategy. Automation is.

Health Checks: The Eyes of the System

Load Balancers use health checks to ask backends "Are you alive?".

L3 Check: Ping. (Is the server on?)
L4 Check: TCP Connect. (Is Nginx listening on port 80?)
L7 Check: HTTP Request to /healthz. (Is the application logic working? Can it talk to the DB?)

Warning: Deep health checks (checking DB connectivity) can cause "Cascading Failure". If the DB slows down, all app servers fail health checks simultaneously, causing a total outage. Use shallow checks for load balancing.

Circuit Breakers

If a microservice is failing, stop calling it. A circuit breaker (in client code) "opens" and returns a default error instantly instead of waiting for a timeout. This gives the failing service time to recover.