Health checks

Periodic probes tell the load balancer which instances can take traffic. A shorter interval detects failures faster but adds load; a deep check that tests the database can take every server out at once if the database blips.

Where it shows up in real systems

  • Application load balancer

    It terminates TLS, routes by path or host and stops sending traffic to an instance that fails its health checks. The algorithm matters: least-connections absorbs uneven requests better than round robin, and sticky sessions create hot spots.

    In production: AWS Application Load Balancer, NGINX, Envoy, HAProxy, Azure Application Gateway

  • Service discovery

    Clients look up where a service lives instead of hard-coding addresses, so instances can come and go during scaling and failures.

    In production: Consul, Kubernetes Services, AWS Cloud Map, Eureka

See it break, then fix it

Build an architecture, send it a day of traffic and outages, and learn why it holds or fails. Free to start.

Open the learning path Open the sandbox