code: protected boolean isActiveInstance(String instanceId, T jedis) {
          boolean isActive = ( System.currentTimeMillis() - getLastInstanceActiveTime(instanceId, jedis) < clusterCheckInterval);
          if (!isActive) {
              removeLastInstanceActiveTime(instanceId, jedis);
          }
          return isActive;
      }
docs: Determine if the instance with the given id has been active in the last 4 minutes
  @param instanceId the instance to check
  @param jedis a thread-safe Redis connection
  @return true if the instance with the given id has been active in the last 4 minutes