What is the process of failover in Hadoop Namenode?

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Failover in Hadoop Namenode refers to the process of transferring the control of the active Namenode to a standby Namenode in the event of a cluster failure or Namenode failure. The following is the process of failover in Hadoop Namenode:

1. Cluster detects the Namenode failure:

The first step in the failover process is for the cluster to detect the failure of the active Namenode. The cluster constantly monitors the health of the Namenode by sending heartbeats to the active server. If the Namenode fails to respond to the heartbeats, the cluster identifies the failure.

1. Standby Namenode takes control:

In the event of Namenode failure, the standby Namenode takes control and becomes the active Namenode. The standby Namenode is constantly updated with the metadata of the active Namenode, which ensures that it has the most up-to-date information.

1. Cluster updates:

After the standby Namenode takes control, the cluster updates the metadata and starts the necessary services that were running on the active Namenode. The clients are then redirected to the new active Namenode so that they can continue accessing the data.

1. Recovery process:

The recovery process involves ensuring that the data in the new active Namenode is consistent with the data in the data nodes. The data nodes are contacted to ensure that they have the most up-to-date data, and any missing data is copied from the other data nodes.

1. Normal operation resumes:

Once the recovery process is completed, the cluster resumes normal operations, and clients can access the data. The failover process is complete, and the new active Namenode continues to serve the clients until the next failure occurs.