code: protected void startMasters(boolean isLeader) {
      try {
        if (isLeader) {
          if (ServerConfiguration.isSet(PropertyKey.MASTER_JOURNAL_INIT_FROM_BACKUP)) {
            AlluxioURI backup =
                new AlluxioURI(ServerConfiguration.get(PropertyKey.MASTER_JOURNAL_INIT_FROM_BACKUP));
            if (mJournalSystem.isEmpty()) {
              initFromBackup(backup);
            } else {
              LOG.info("The journal system is not freshly formatted, skipping restoring backup from "
                  + backup);
            }
          }
          mSafeModeManager.notifyPrimaryMasterStarted();
        } else {
          startRejectingServers();
        }
        mRegistry.start(isLeader);
        LOG.info("All masters started");
      } catch (IOException e) {
        throw new RuntimeException(e);
      }
    }
docs: Starts all masters, including block master, FileSystem master, and additional masters.
  
  @param isLeader if the Master is leader