default void preListReplicationPeers(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    String regex) throws IOException {
  }
Called before list replication peers.
@param ctx   the environment to interact with the framework and master
@param regex The regular expression to match peer id
hbase-server/src/main/java/org/apache/hadoop/hbase/coprocessor/MasterObserver.java