If a new indexer is added to the cluster. Do we need to manually push the cluster-bundle from master to indexers OR Cluster-bundle will be automatically pushed to new indexer once it communicates with the master?
The indexer automatically downloads the bundle.
Discussed in the docs here: http://docs.splunk.com/Documentation/Splunk/7.1.0/Indexer/Updatepeerconfigurations#Distribution_of_t...
I couldn't find a reference that details the process in the docs, but in my experience new indexers get the bundle and are ready for production use immediately.