Resource health checks
Health checks are used by the load balancer to get information about the health of resources in an attached target group. In response to a health request, resources report that they are ready to receive traffic or has failed. Checks are performed via TCP or HTTP at the intervals specified in the configuration.
The following should be specified for each check:
- Check interval, from 1 to 300 seconds.
- Check timeout, from 1 to 60 seconds. The timeout is the time allowed for the resource to respond to a check. If the resource doesn't respond in time, the check is considered failed and the resource is assigned the
- Resource health indicators: the number of sequential successful or failed checks, which, when reached, would indicate whether a resource is considered available or unavailable.
For HTTP checks, the target URL for a verification request is specified.
Target resource health statuses
A target can have one of the following health statuses:
INITIAL: A health check is being configured for the resource.
HEALTHY: The resource is running and ready to receive traffic.
UNHEALTHY: The resource is not ready to receive traffic.
DRAINING: The resource is being deleted and traffic is being removed from it. The load balancer stops routing traffic to this resource.
INACTIVE: The resource is attached to a stopped load balancer or a load balancer without any listeners.
There is a delay between changing a resource's status to
UNHEALTHY and the time when the load balancer stops routing traffic to the resource. This is the time that the load balancer requires to process health check results.
Health checks are transmitted to target resources from IP addresses in the following ranges:
198.18.248.0/24. Traffic filtering rules configured for targets must support incoming traffic from addresses in this range. Otherwise, no checks will be performed. As a result, the targets will not be assigned the
HEALTHY status and will not be able to receive traffic.
When performing HTTP verification, a resource gets the
HEALTHY status only when responding with code