Both I suppose.
The indexers will need the os index on them and the Search head will need the app. I'm using the TA for *nix on the forwarders.
So what you want is Distributed Search to search knowledge objects on your search head and Clustering for your indexers. Additionally you will want to use the Deployment server or Puppet to deploy your apps like the Nix app.
I familar witht he process but, the best I can do for you is point you to the documentation for each component. The setup will vary depending on your Operational requirement and budget. Be aware that 5.x Clustering duplicates the all indices on your Indexer.
Hope this helps or gets you started. Dont forget to thumbs up or accept answers that help. Cheers,