The cluster is always green, with no relocating, initializing, unassigned or pending tasks.
In my previous configuration, I had all nodes setup as masterdata role on the same physical machines, there was no issue in bulk indexing, but since there were a lot of indices, memory was running out and since all were masters, the cluster was unstable.
So recently, I did two things. (1) upgraded from 1.7 to 2.1 (2) went from masterdata to seperate master, client and data roles.
Ever since I moved to this configuration, which I thought was better on higher QPS and higher no. of indices, even though cluster is stable, I have been seeing a lot of errors while doing bulk indexing. The two errors I see are (1) 504s - underlying connection was closed (2) in the bulk response 50% of the documents always come back with the error queue full.