anchor.diff:  
   For example, changing the number of replicas on the leader index is not
   replicated by the follower index, so that setting might not be retrieved.
  -
  -NOTE: You cannot manually modify a follower index's mappings or aliases.
   
   If you apply a non-dynamic settings change to the leader index that is
   needed by the follower index, the follower index closes itself, applies the
  
positive.code: follower shard pauses
  <<ccr-pause-replication,until you resume it>>.
  
  When a follower shard receives operations from the leader shard, it places
  those operations in a write buffer. The follower shard submits bulk write
  requests using operations from the write buffer. If the write buffer exceeds
  
negative.code: 
  image::images/ccr-arch-bi-directional.png[Bi-directional configuration where each cluster contains both a leader index and follower indices]
  
  This configuration is particularly useful for index-only workloads, where no updates
  to document values occur. In this configuration, documents indexed by {es} are
  immutable. Clients are located in each datacenter alongside the {es}
  cluster, and do not communicate with clusters in different datacenters.
  