Health checks for instances in an Auto Scaling group
Amazon EC2 Auto Scaling continuously monitors the health status of instances in an Auto Scaling group to maintain the desired capacity.
All instances in an Auto Scaling group start with a Healthy
status. Instances are
assumed to be healthy unless Amazon EC2 Auto Scaling receives notification that they are unhealthy. It can
receive notifications from various sources when an instance becomes unhealthy and needs to
be replaced. These sources include:
Amazon EC2
Elastic Load Balancing
VPC Lattice
Custom health checks that you define
When Amazon EC2 Auto Scaling determines that an InService
instance is unhealthy, it replaces
it with a new instance to maintain the desired capacity of the group. The new instance
launches using the current settings of the Auto Scaling group and its associated launch template or
launch configuration.
Unhealthy instances can also occur when an instance terminates unexpectedly, such as from a Spot Instance interruption or manual termination by a user. Again, Amazon EC2 Auto Scaling will automatically launch a replacement instance in these cases to maintain the desired capacity.