Why is my EC2 Auto Scaling group stuck in "Updating capacity"?

Short description

If the desired capacity is higher than the group's total capacity, then an EC2 Auto Scaling group can be stuck in the Updating capacity state.

For example, you set the desired capacity to 10. However, the capacity of your group is five. In this case, the group can't reach the desired capacity because it's higher than the current capacity.

To determine why the capacity that you set can't reach the capacity of the group, complete the following steps.

Resolution

Suspended processes

If one or more processes are suspended, then your EC2 Auto Scaling group might not be able to launch or terminate instances. To reach the desired capacity, you must launch or terminate instances.

To resolve this issue, resume the suspended processes.

Launch or termination failure

Look in the group history to determine if your EC2 Auto Scaling group successfully launched or terminated instances. The scaling activity might still be in progress. For information about how to view scaling activities, see Verify a scaling activity for an Auto Scaling group.

Launch failure

If a launch failed, then see Troubleshoot Amazon EC2 Auto Scaling: EC2 instance launch failures.

Terminate failure

Check for the following error message:

"Could not terminate instances due to invalid response from custom termination policy. Status Reason: Customer's response from lambda was not decodable."

If you see this message, then the failure might be related to a custom termination policy with AWS Lambda.

To resolve this issue, check your Lambda function to make sure that Lambda can return the instances that are ready to terminate.