Set the health check grace period for an Auto Scaling group

When an Amazon EC2 Auto Scaling health check determines that an InService instance is unhealthy, it replaces it with a new instance. The health check grace period specifies the minimum amount of time (in seconds) to keep a new instance in service before terminating it if it's found to be unhealthy.

An example use case might be a requirement for Amazon EC2 Auto Scaling to avoid taking action if the Elastic Load Balancing health checks fail and the cause is that the instance is still initializing. Elastic Load Balancing health checks run in parallel, starting when the instance is registered with the load balancer. The grace period prevents Amazon EC2 Auto Scaling from marking your newly launched instances Unhealthy and terminating them unnecessarily if they do not immediately pass these health checks after they enter the InService state.

In the console, by default, the health check grace period is 300 seconds when you create an Auto Scaling group. Its default value is 0 seconds when you create an Auto Scaling group using the AWS CLI or an SDK. A value of 0 turns off the health check grace period.

Setting this value too high reduces the effectiveness of the Amazon EC2 Auto Scaling health checks. If you use lifecycle hooks for instance launch, you can set the health check grace period to 0. With lifecycle hooks, Amazon EC2 Auto Scaling provides a way to make sure that instances are always initialized before they enter the InService state. For more information, see Amazon EC2 Auto Scaling lifecycle hooks.

The grace period applies to the following instances:

Set the health check grace period for a group

You can set the health check grace period for new and existing Auto Scaling groups.

Console

To modify the health check grace period for a new group (console)

When you create the Auto Scaling group, on the Configure advanced options page, for Health checks, Health check grace period, enter the amount of time, in seconds. This is how long Amazon EC2 Auto Scaling needs to wait before checking the health status of an instance after it enters the InService state.

AWS CLI

To modify the health check grace period for a new group (AWS CLI)

Add the --health-check-grace-period option to the create-auto-scaling-group command. The following example configures the health check grace period with a value of 60 seconds for a new Auto Scaling group named my-asg.

aws autoscaling create-auto-scaling-group --auto-scaling-group-name my-asg --health-check-grace-period 60 ...

Console

To modify the health check grace period for an existing group (console)

1. Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/, and choose Auto Scaling Groups from the navigation pane.

2. On the navigation bar at the top of the screen, choose the AWS Region that you created your Auto Scaling group in.

3. Select the check box next to the Auto Scaling group.

   A split pane opens up in the bottom of the page.

4. On the Details tab, choose Health checks, Edit.

5. Under Health check grace period, enter the amount of time, in seconds. This is how long Amazon EC2 Auto Scaling needs to wait before checking the health status of an instance after it enters the InService state.

6. Choose Update.

AWS CLI

To modify the health check grace period for an existing group (AWS CLI)

Add the --health-check-grace-period option to the update-auto-scaling-group command. The following example configures the health check grace period with a value of 120 seconds for an existing Auto Scaling group named my-asg.

aws autoscaling update-auto-scaling-group --auto-scaling-group-name my-asg --health-check-grace-period 120