code: private void prepareFailover() {
      LOG.info("PREPARE FAILOVER requested by : " + this.avatarnodeAddress);
      // we should start sending incremental block reports and block
      // reports normally
      setBackoff(false);
      this.donotDelayIncrementalBlockReports = true;
      InjectionHandler.processEvent(InjectionEvent.OFFERSERVICE_PREPARE_FAILOVER,
          nsRegistration.toString());
    }
docs: Take actions in preparation for failover.