This is a mandatory Splunk component when implementing a search head cluster, as it is responsible for distributing the configuration updates and app bundles to the cluster members1. The deployer is a separate instance that communicates with the cluster manager and pushes the changes to the search heads1. The other options are not mandatory components for a search head cluster. Option A, Captain Server, is not a component, but a role that is dynamically assigned to one of the search heads in the cluster2. The captain coordinates the replication and search activities among the cluster members2. Option C, Cluster Manager, is a component for an indexer cluster, not a search head cluster3. The cluster manager manages the replication and search factors, and provides a web interface for monitoring and managing the indexer cluster3. Option D, RAFT Server, is not a component, but a protocol that is used by the search head cluster to elect the captain and maintain the cluster state4. Therefore, option B is the correct answer, and options A, C, and D are incorrect.

1: Use the deployer to distribute apps and configuration updates 2: About the captain 3: About the cluster manager 4: How a search head cluster works