What is Heartbeat in Hadoop? How to resolve Heartbeat lost in Cloudera and Hortonworks

Heartbeat in Hadoop:





In Hadoop, eco-system Heartbeat is an in-between Namenode and Datanode communication. It is the signal that is sent by the Datanode to Namenode after a regular interval. If Datanode in HDFS does not send a heartbeat to Namenode around 10 minutes by default then Namenode considers the Datanode is not available.

The default heartbeat interval is 3 seconds. Put in dfs.heartbeat.interval in a hdfs-site.xml file in Hadoop installation directory.

What is Heartbeat lost:

In Hadoop eco-system, the Datanode does not send a heartbeat to Namenode around 10 minutes by default. So, in this case, Namenode considers a Datanode is unavailable it is known as “Heartbeat lost”.

How to resolve Heartbeat lost:

In Bigdata distribution environment will take Hortonworks (HDP)In Hortonworks:
1. In HDP check Amabari agents status whether it is running or not by using” ambari-agent status ”
2. If it is not running then check with log files for Ambari server and Ambari agent as well as in the directory of /var/log/ambari-server and /var/log/ambari-agent.

3. Follow the below steps:

A) Stop ambari-server
B) Stop ambari-agent service on all nodes
C) Start ambari-agent service on all nodes
D) Start ambari-server server

Cloudera:

1. First Check the Cloudera scm agent status whether it is running or not by using” sudo service cloudera-scm-agent status ”





2.check the agent log files in this directory in /var/log/cloudera-scm-agent/

2. Then follow the below commands with root user

sudo service cloudera-scm-agent status
sudo service cloudera-scm-agent stop
sudo service cloudera-scm-agent start

Summary: Hadoop is following Master, Slave architecture. The master node stores the metadata and slave nodes stores the actual data. So while sending data communication between Namenode and Datanode is called as a “Heartbeat”. If it fails simply called as a “Heartbeat lost” it means that Datanode is unavailable.  To find resolution steps for Bigdata distributions like Hortonworks (HDP) and Cloudera (CDH) with step by step process for this issue.