An engineer sets up a CloudWatch alarm to run the built-in "Recover this instance" action on a StatusCheckFailed_System alarm, expecting it to work uniformly across the whole fleet, which includes some instances using local instance store volumes, some using Dedicated Host tenancy, and some bare-metal instance types. What should the engineer expect?
- The recover action is guaranteed to work identically across all of these instances, since any instance with an EC2 status check can be recovered
- The recover action is unavailable for instances that use instance store volumes, for instances running with Dedicated Host tenancy, and for bare-metal instance types; only a subset of instance types and configurations support it
- The recover action only fails for bare-metal instance types; instance store volumes and Dedicated Host tenancy have no effect on eligibility
- The recover action is unavailable for every instance except those using Dedicated Host tenancy, since that tenancy model is specifically designed to support automated recovery
Why B? And why not the others?
Correct answer: B. The recover action is unavailable for instances that use instance store volumes, for instances running with Dedicated Host tenancy, and for bare-metal instance types; only a subset of instance types and configurations support it
CloudWatch alarm-based recovery for EC2 does not support every instance uniformly: instances that use instance store volumes are ineligible (the recover option is grayed out for them because instance store data can't survive the underlying migration to new hardware that recovery performs), and separately, recovery is not supported for instances running with Dedicated Host tenancy or for bare-metal instance types, since both bypass the standard virtualized recovery path recovery depends on; only a defined subset of instance types and configurations actually support the action. The option claiming uniform support across the whole fleet ignores all three of these documented restrictions. The option claiming only bare-metal instance types are affected understates the restriction, since instance store volumes and Dedicated Host tenancy each independently disqualify an instance too. The option claiming only Dedicated Host tenancy is supported has it backwards: Dedicated Host tenancy is one of the configurations recovery does not support, not the one configuration it's designed around.
Source: AWS EC2 documentation: Recover your instance / Configure CloudWatch action-based recovery — instance store, Dedicated Host, and bare-metal restrictions