To set up Cluster you'll need to:
- Set up DFS Cluster which moves binary files to NFS
- Configure Persistence Cache to use Memcached or Redis
- Set up Varnish, disable Symfony HTTP Cache and set up cache invalidation to purge Varnish cache
- to use a cluster safe sessions handling
It is also highly recommended to set up Solr Bundle to be able to get better search, better query performance, be able to scale it, and offload database.