A solutions architect has launched multiple Amazon EC2 instances in a placement group within a single Availability Zone. Because of additional load on the system, the solutions architect attempts to add new instances to the placement group. However, the solutions architect receives an insufficient capacity error. What should the solutions architect do to troubleshoot this issue?

An insufficient capacity error when adding instances to a cluster placement group indicates that AWS cannot find contiguous underlying hardware to co-locate the new instance with the existing ones. A recommended troubleshooting strategy is to stop all instances within the placement group and then start them again. This action may migrate the entire group to a different set of underlying hardware that has sufficient capacity to accommodate both the existing and the new instances. This approach attempts to resolve the capacity issue without requiring architectural changes.

A. A spread placement group has a hard limit of seven running instances per Availability Zone, so setting a minimum of eight is not possible. This also changes the architecture's intent.
C. AWS does not provide a feature to merge two placement groups. This is not a valid operation.
D. Launching on Dedicated Hosts is a significant architectural and cost change. It is not the most direct or common first step to troubleshoot a transient capacity error.

1. Amazon EC2 User Guide for Linux Instances: Under the section "Troubleshoot placement groups," the guide explicitly states: "If you receive a capacity error when launching an instance in a placement group that already has running instances, stop and start all of the instances in the placement group, and then try the launch again. Starting the instances may migrate them to hardware that has capacity for all the requested instances." (See section: Placement groups > Troubleshoot placement groups).

2. Amazon EC2 User Guide for Linux Instances: The section on "Spread placement groups" details the limitations: "A spread placement group can span multiple Availability Zones within the same Region, and you can have a maximum of seven running instances per Availability Zone per group." This confirms that option A is invalid. (See section: Placement groups > Spread placement groups).

3. AWS API Reference - CreatePlacementGroup: The documentation for creating and managing placement groups does not include any action or parameter for merging existing groups, confirming that option C is not a valid AWS feature. (See the CreatePlacementGroup and related EC2 API actions in the AWS Command Line Interface Reference or SDK documentation).