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Chapter 1 # Introduction to the Node Management Agent This chapter describes how to access the Node Management Agent (NMA) and introduces the master node view and the floating external address. The NMA is a management agent that conforms to the Java Management Extensions (JMX) v1.1 Maintenance Release. The NMA is based on the Java Dynamic Management Kit (DMK) 5.0 APIs. The NMA monitors the performance and the status of the following Foundation Services: Cluster Membership Manager Carrier Grade Transport Protocol (CGTP) Daemon Monitor Reliable NFS The NMA exposes this information through a Simple Network Management Protocol (SNMP) management information base (MIB) and a JMX compliant interface. The JMX specification defines a three-level management architecture: The instrumentation level makes resources manageable as Java objects called MBeans. The agent level exposes these objects for management. The distributed services level allow remote access and security. By programmatically accessing these MBeans, management applications can be used to help perform tuning operations, diagnostic operations, and troubleshooting. The NMA also provides a method for provoking a master node switchover, and emits notifications which can be used to keep up-to-date with the current state of certain aspects of the cluster. The Java DMK implements the JMX specification. The NMA requires the Java DMK runtime libraries. You can use the Java DMK to develop a remote Java manager to access the NMA. Alternately, access the NMA MIB by using an off-the-shelf or custom SNMP manager, or any JMX compliant Java manager. This chapter contains the following sections: Accessing the NMA Master and Node Views Floating External Address ## Accessing the NMA An external manager can communicate with the NMA using any of the following protocols: HTTP SNMP version 1 (SNMPv1) SNMP version 2 (SNMPv2) SNMP version 3 (SNMPv3) Note - The floating external address cannot be used when you are using the SNMP protocol. See Floating External Address for more information on the floating external address. Use SNMPv3 to take advantage of the enhanced security mechanism introduced in SNMPv3. Note that not all protocol interfaces are enabled by default. See `nma.properties`(4) for information on how to enable, disable and configure protocol interfaces. HTML can be used to view the NMAs in a running cluster through an HTML browser. By default port `8082` exports this view. To interact with the NMA on a node, access the URL of the form `http://nodeIPAddress:portNumber` See "HTML Protocol Adaptor" in the Java Dynamic Management Kit 5.0 Tutorial for more information. Note that if you provoke a switchover using the HTML Protocol Adaptor connected to the floating external address, the connection to the NMA might be broken prematurely and the information transfer will not finish. If this happens, stop the transfer and reload the page to get the correct node information. Figure 1-1 represents the communication paths between an external manager and the cluster: Figure 1-1 Remote Manager Communication ## Master and Node Views The NMA running on the master node makes information from the NMAs running on all nodes visible in the NMA running on the master node through a cascading connection. The MBeans listed in MBean Instances on the Master Node are available on the master node only. Figure 1-2 shows how information is cascaded from all NMAs to the NMA on the master node. Figure 1-2 Cascading Information From Peer Nodes to the Master Node Note - The master view is only available to a Java manager that communicates using the HTTP protocol. All of the agents must use the same port number for the service used to implement cascading. If this is not the case, the master agent will start the cascading service but will not enable the cascading connections to NMA. Note - After failover or switchover, there is a short period of time during which the NMA information of other nodes is made available on the new master. If you query this information from the master during this period, an exception will be thrown. Cascading is controlled by the following properties, which are defined in the `nma.properties` file:
`com.sun.nhas.ma.cascading.enabled` | Set to `true` to enable cascading.
`com.sun.nhas.ma.cascading.retries.max` | The maximum number of times that the master node tries to create a cascading connection to an NMA on another node.
`com.sun.nhas.ma.cascading.retries.delay` | The time in milliseconds between each attempt to establish a cascading connection.
`com.sun.nhas.ma.cascading.comm.protocol` | The protocol can be `http` or `rmi`.
`com.sun.nhas.ma.cascading.socket.timeout.wait` | The timeout in milliseconds for a cascading connection to terminate cleanly in the case of a communication fault. After this time has elapsed, the cascading connection attempt will be forcibly aborted and then restarted.
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