This interface layer handles the communication between the NameNode and DataNode component of the Apache Hadoop cluster charms.

The NameNode requires this interface, to gain access to one or more DataNode units.

This interface layer will set the following states, as appropriate:

• {relation_name}.joined One or more DataNodes have connected. The charm should call the following methods to provide the appropriate information to the DataNodes:

  • send_spec(spec)
  • send_host(host)
  • send_ports(port, webhdfs_port)
  • send_ssh_key(ssh_key)
  • send_hosts_map(hosts_map)

• {relation_name}.departing One or more DataNodes are about to depart, and the NameNode should remove them from the pool of slaves. Information about the departing DataNodes can be gotten from the method:

  • datanodes()

This interface layer will set the following states, as appropriate:

• {relation_name}.joined The relation is established, but HDFS may not yet have provided any connection or service information.

• {relation_name}.ready The NameNode has provided all of the necessary information, and this unit is present in the hosts map, indicating that it can be seen by the NameNode and all other DataNodes. The provided information can be accessed via the following methods:

  • spec()
  • host()
  • port()
  • webhdfs_port()
  • ssh_key()
  • hosts_map()

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