The default push mode for a search head cluster deployer app configuration bundle is full. This means that the deployer pushes the entire app configuration bundle to the search head cluster members, overwriting any existing app configurations on the members. The full push mode ensures that the app configurations are consistent and synchronized across the cluster. The other push modes are merge_to_default, default_only, and local_only, which have different effects on how the app configurations are merged or overwritten on the cluster members. Therefore, the correct answer is A. full. References:

Splunk Core Certified Consultant Test Blueprint

Splunk Documentation: Deploy apps to a search head cluster

Splunk Documentation: Push configuration bundle