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AdventNet SNMP for EJB has been designed to support EJB applications, and conform to the EJB standards. The EJB standard restricts the Enterprise Java Bean from performing certain functions, such as socket access. In order to perform protocol operations, such as receiving traps while conforming to the EJB standard, an architecture suitable for SNMP operations for EJB is required. AdventNet SNMP API provides a solution to this.
The protocol-specific functions needed by EJB components are provided by the SnmpEJBServer factory that runs outside the EJB container. This operates in a similar fashion to the SNMP RMI factory. This provides the SNMP protocol operations, such as accessing sockets, receiving traps, polling, and so on, which are not permitted in Enterprise Java Beans. These server functions are implemented using AdventNet's SNMP support for RMI.
The Enterprise Java Beans use the SnmpEJBServer to create SNMP bean instances for protocol operations as required. These bean instances are used by the EJBs and garbage collected when the EJB instance is deleted, or when specifically de-referenced by the EJB. EJBs need to take of passivation, i.e. where the EJB is temporarily removed from memory and serialized to disk, because RMI references are not restored when the EJB instance is restored to memory. The EJB needs to use the JNDI to cache the RMI reference when it is being passivated. Future releases of AdventNet SNMP EJB will simplify this process and offer pooling of the SNMP bean instances.
AdventNet provides the SNMP EJBs that can be used with this architecture. This release includes Session EJBs for synchronous SNMP operations and SNMP table support. More EJBs will be provided shortly. Application developers will build their own EJBs for specific SNMP-enabled applications, which can use the provided SNMP EJBs or directly use the SnmpEJBServer.
The web container with JSP and Servlet pages connects to the EJBs to serve clients, as per the typical EJB Application Architecture. The HTML clients connect to the web container, which serves the HTML pages over HTTP. The Java clients may use the web container, but more often directly connect to the Session EJBs within the EJB container, using JNDI look-up and the home interfaces to get access to the EJB instances.
The architecture for SNMP for EJB is illustrated below.
The EJB does a JNDI look-up for the SnmpEJBServer, which permits clustering and load balancing of multiple SnmpEJBServer factories, when using clustering with the application server. Support for these capabilities vary with the particular application server being used. Typically, multiple SnmpEJBServer instances would be deployed on different servers, and using JNDI naming, the deployed EJBs will be load balanced over these SnmpEJBServer instances.
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