Associate instances

By instance ID

aws ec2 associate-application-status-check \
  --application-status-check-id "$ASC_ID" \
  --instance-ids "$INSTANCE_ID"

Associate and disassociate calls return per-instance success and failure. If a check is already associated, that instance appears in the unsuccessful list with a reason.

By tag

Lab from Create VPC and EC2:

aws ec2 associate-application-status-check \
  --application-status-check-id "$ASC_ID" \
  --target-tag-associations Key=asc-lab,Value=true

Production-style example:

aws ec2 associate-application-status-check \
  --application-status-check-id asc-0123456789abcdef0 \
  --target-tag-associations Key=Environment,Value=production

Tag associations are rules. Each rule counts as one association toward quotas, regardless of how many instances currently match.

Auto Scaling group

Amazon EC2 Auto Scaling stamps every instance with aws:autoscaling:groupName. Associate once; new launches pick up the check.

aws ec2 associate-application-status-check \
  --application-status-check-id asc-0123456789abcdef0 \
  --target-tag-associations Key=aws:autoscaling:groupName,Value=my-asg

No launch template change is required.

Caution

Leave aggregation excluded until you have verified results on a canary instance or a small tag set. Flip to included only after describe-application-status looks right for at least two intervals (about two minutes).

Disassociate

By instance ID:

aws ec2 disassociate-application-status-check \
  --application-status-check-id asc-0123456789abcdef0 \
  --instance-ids i-0123456789abcdef0

If you associated by tag, remove the tag from the instance (or disassociate the tag rule). After disassociation, overall status is not-applicable.

Next

Verify in the console and CLI before you include the check in aggregation. With excluded, the instance Status and alarms card shows Application status as None associated or included.