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Amazon EC2 Auto Scaling
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AWS Documentation » Amazon EC2 Auto Scaling » User Guide » Auto Scaling Groups » Using a Load Balancer with an Auto Scaling Group » Adding Elastic Load Balancing Health Checks to an Auto Scaling Group
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Adding Elastic Load Balancing Health Checks to an Auto Scaling Group

The default health checks for an Auto Scaling group are EC2 status checks only. If an instance fails these status checks, the Auto Scaling group considers the instance unhealthy and replaces it. For more information, see Health Checks for Auto Scaling Instances.

If you attached one or more load balancers or target groups to your Auto Scaling group, the group does not, by default, consider an instance unhealthy and replace it if it fails the load balancer health checks.

However, you can optionally configure the Auto Scaling group to use Elastic Load Balancing health checks. This ensures that the group can determine an instance's health based on additional tests provided by the load balancer. The load balancer periodically sends pings, attempts connections, or sends requests to test the EC2 instances. These tests are called health checks.

To learn more about Elastic Load Balancing health checks, see the following topics:

If you configure the Auto Scaling group to use Elastic Load Balancing health checks, it considers the instance unhealthy if it fails either the EC2 status checks or the load balancer health checks. If you attach multiple load balancers to an Auto Scaling group, all of them must report that the instance is healthy in order for it to consider the instance healthy. If one load balancer reports an instance as unhealthy, the Auto Scaling group replaces the instance, even if other load balancers report it as healthy.

The following procedures show how to add Elastic Load Balancing health checks to your Auto Scaling group.

Adding Health Checks (Console)

Use the following procedure to add an ELB health check with a grace period of 300 seconds to an Auto Scaling group with an attached load balancer.

To add health checks

  1. Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/.

  2. On the navigation pane, under Auto Scaling, choose Auto Scaling Groups.

  3. Choose an existing group from the list.

  4. On the Details tab, choose Edit.

  5. For Health Check Type, select ELB.

  6. For Health Check Grace Period, enter 300.

  7. Choose Save.

  8. On the Instances tab, the Health Status column displays the results of the newly added health checks.

Adding Health Checks (AWS CLI)

Use the following update-auto-scaling-group command to create a health check with a grace period of 300 seconds. 

aws autoscaling update-auto-scaling-group --auto-scaling-group-name my-lb-asg \
  --health-check-type ELB --health-check-grace-period 300