Courses / AWS
47. Instance health vs ELB health
Distinction between ASG-managed instance health checks and load-balancer health checks.
AWS / Infrastructure as Code
Instance health vs ELB health
ASG instance health is the Auto Scaling group's view of whether an EC2 is functioning, while ELB health is whether the load balancer successfully routes traffic to that instance.
"I marked my instance healthy, so why is traffic still not reaching it?"
Auto Scaling Groups (ASG) perform EC2 health checks to decide lifecycle actions; Elastic Load Balancers (ELB/ALB/NLB) perform separate health checks to decide whether to send traffic to an instance. They can disagree, and each drives different behavior.
"I marked my instance healthy, so why is traffic still not reaching it?"
Auto Scaling Groups (ASG) perform EC2 health checks to decide lifecycle actions; Elastic Load Balancers (ELB/ALB/NLB) perform separate health checks to decide whether to send traffic to an instance. They can disagree, and each drives different behavior.