Health Checks

Load balancer health check service

One of the most important services a load balancer can provide is service health checks. The load balancer will not send traffic to an instance that fails a certain number of health checks. Both the frequency and number of failed checks are configurable per pool. Refer back to Health Checks for some details about good health checks.

Stickiness

Load balancers can also attempt to direct repeated requests to the same instance. This helps when we have stateful services, like user session state, in an application server. Directing the same requests to the same instances will provide better response time for the caller because necessary resources will already be in that instance’s memory.

A downside of sticky sessions is that they can prevent a load from being distributed evenly across machines. We may find a machine running “hot” for a while if it happens to get several long-lived sessions.