Which additional component is required for a search head cluster?

[Reference:https://docs.splunk.com/Documentation/Splunk/8.0.5/DistSearch/SHCdeploymentoverview, , The deployer. This is a Splunk Enterprise instance that distributes apps and other configurations to the cluster members. It stands outside the cluster and cannot run on the same instance as a cluster member. It can, however, under some circumstances, reside on the same instance as other Splunk Enterprise components, such as a deployment server or an indexer cluster master node., , , ]