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What is an Auto Scaling Group in AWS and what problem does it solve? What is a launch template and how is it used by an Auto Scaling Group? What scaling policies are available in Auto Scaling Groups, such as target tracking and step scaling? How can Auto Scaling Groups span multiple Availability Zones to improve application availability? How do lifecycle hooks in Auto Scaling Groups let you customize instance launch and termination behavior? How can predictive scaling in Auto Scaling Groups improve upon reactive scaling policies?
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How do health checks work within an Auto Scaling Group to maintain a healthy fleet of instances?

Intermediate

Answer

An Auto Scaling Group continuously monitors the health of its instances using either EC2 status checks or, if configured, Elastic Load Balancer health checks, and whenever an instance is found to be unhealthy, the Auto Scaling Group automatically terminates that instance and launches a replacement, ensuring the group always maintains its desired capacity of healthy, functioning instances.
aws autoscaling update-auto-scaling-group --auto-scaling-group-name my-asg --health-check-type ELB --health-check-grace-period 300
Real-world example A web application configures its Auto Scaling Group to use Elastic Load Balancer health checks rather than basic EC2 checks, ensuring that instances failing to respond correctly to application level requests are replaced even if the underlying EC2 instance itself appears technically healthy.

Common follow-ups: What is the health check grace period and why is it needed?;What is the difference between EC2 status checks and ELB health checks?

Elastic Load Balancing (ALB NLB & CLB);Monitoring (CloudWatch)
All 7 Auto Scaling Groups questions