In the context of configuring a Hadoop cluster for HDFS High Availability (HA), `fencing' refers to:

Question

Options

• AIsolating a failed NameNode from write access to the fsimage and edits files so that is cannot resume
• BIsolating the cluster's master daemon to limit write access only to authorized clients.
• CIsolating both HA NameNodes to prevent a client application from killing the NameNode daemons.
• DIsolating the standby NameNode from write access to the fsimage and edits files.

• A
  75% (39)
• B
  15% (8)
• C
  6% (3)
• D
  4% (2)

Explanation

A fencing method is a method by which one node can forcibly prevent another node from making continued progress. This might be implemented by killing a process on the other node, by denying the other node's access to shared storage, or by accessing a PDU to cut the other node's power. Since these methods are often vendor- or device-specific, operators may implement this interface in order to achieve fencing. Fencing is configured by the operator as an ordered list of methods to attempt. Each method will be tried in turn, and the next in the list will only be attempted if the previous one fails. See NodeFencer for more information. failover - initiate a failover between two NameNodes This subcommand causes a failover from the first provided NameNode to the second. If the first NameNode is in the Standby state, this command simply transitions the second to the Active state without error. If the first NameNode is in the Active state, an attempt will be made to gracefully transition it to the Standby state. If this fails, the fencing methods (as configured by dfs.ha.fencing.methods) will be attempted in order until one of the methods succeeds. Only after this process will the second NameNode be transitioned to the Active state. If no fencing method succeeds, the second NameNode will not be transitioned to the Active state, and an error will be

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