@Override
  public boolean test(SyncReplicationState state, SyncReplicationState newState) {
    // reject requests from client if we are in standby state, or we are going to transit to standby
    // state.
    return state == SyncReplicationState.STANDBY || newState == SyncReplicationState.STANDBY;
  }
Check whether we need to reject the request from client.
hbase-server/src/main/java/org/apache/hadoop/hbase/replication/regionserver/RejectRequestsFromClientStateChecker.java