View the reason for health check
failures
Using the following procedure, you can view information about any instances replaced
due to a health check.
By default, Amazon EC2 Auto Scaling creates a new scaling activity for terminating the unhealthy
instance and then terminates it. While the instance is terminating, another scaling
activity launches a new instance. You can change this behavior to start launching a new
instance as soon as possible by using an instance maintenance policy. For more
information, see Instance maintenance
policies.
- Console
-
Viewing the reason for health check failures
Open the Amazon EC2 console at
https://console.aws.amazon.com/ec2/, and choose Auto Scaling Groups from the navigation pane.
-
Select the check box next to the Auto Scaling group.
A split pane opens up in the bottom of the Auto Scaling
groups page.
-
On the Activity tab, under Activity
history, the Status column shows
whether your Auto Scaling group has successfully launched or terminated
instances.
If it terminated any unhealthy instances, the
Cause column shows the date and time of the
termination and the reason for the health check failure. For
example, At 2022-05-14T20:11:53Z an instance was taken
out of service in response to a user
health-check
. This message indicates that a
custom health check marked the instance unhealthy.
For help with health check failures, see Troubleshoot unhealthy instances in Amazon EC2 Auto Scaling.
- AWS CLI
-
Viewing the reason for health check failures
Use the following describe-scaling-activities command.
aws autoscaling describe-scaling-activities --auto-scaling-group-name my-asg
The following is an example response, where Cause
contains
the reason for the health check failure.
{
"Activities": [
{
"ActivityId": "4c65e23d-a35a-4e7d-b6e4-2eaa8753dc12",
"AutoScalingGroupName": "my-asg",
"Description": "Terminating EC2 instance: i-04925c838b6438f14",
"Cause": "At 2021-04-01T21:48:35Z an instance was taken out of service in response to a user health-check.",
"StartTime": "2021-04-01T21:48:35.859Z",
"EndTime": "2021-04-01T21:49:18Z",
"StatusCode": "Successful",
"Progress": 100,
"Details": "{\"Subnet ID\":\"subnet-5ea0c127\",\"Availability Zone\":\"us-west-2a\"...}",
"AutoScalingGroupARN": "arn:aws:autoscaling:us-west-2:123456789012:autoScalingGroup:283179a2-f3ce-423d-93f6-66bb518232f7:autoScalingGroupName/my-asg"
},
...
]
}
For a description of the fields in the output, see Activity in
the Amazon EC2 Auto Scaling API Reference.
To describe the scaling activities after the Auto Scaling group has been
deleted, add the --include-deleted-groups
option to the
describe-scaling-activities command.