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javaoracle11gcluster-computingoracle-fusion-middleware

how managed servers listen to each other in server cluster

when configuring oracle fusion middleware, in the screen for 'managed cluster servers' user has to enter managed server name and listening port. how it's working on a cluster, is the server listening on the port of the given ip address, if it's so it's confusing to think how one server is listening to a external machine. for example serverA listens on ServerB port 20 and whenever serverB sends data through port 20, serverA has to pick them up! in that case ServerA has a listener on external machines port, is it possible?

Solution

  • Managed Servers host business applications, application components, Web services, and their associated resources. To optimize performance, Managed Servers maintain a read-only copy of the domain's configuration document. When a Managed Server starts, it connects to the domain's Administration Server to synchronize its configuration document with the document that the Administration Server maintains.

    For production environments that require increased application performance, throughput, or high availability, you can configure two or more Managed Servers to operate as a cluster. A cluster is a collection of multiple WebLogic Server instances running simultaneously and working together to provide increased scalability and reliability. In a cluster, most resources and services are deployed identically to each Managed Server (as opposed to a single Managed Server), enabling failover and load balancing. A single domain can contain multiple Oracle WebLogic Server clusters, as well as multiple Managed Servers that are not configured as clusters. The key difference between clustered and nonclustered Managed Servers is support for failover and load balancing. These features are available only in a cluster of Managed Servers.

    The following diagram from the Oracle website would be helpful to understand the "Oracle Fusion Middleware Environment"

    enter image description here

    Oracle Fusion Middleware cluster instances communicate with each other using the following network technologies:

    1. IP sockets (for peer-to-peer communication between clustered server instances)
    2. IP multicast or unicast (used by server instances to broadcast availability of services and heartbeats indicating continued availability)

    a) Using IP Multicast: Cluster Instances uses IP multicast for all one-to-many communications among server instances in a cluster. This communication includes:

    • Each server instance in a cluster uses multicast to announce the availability of clustered objects that are deployed or removed locally. Each server instance in the cluster monitors these announcements and updates its local JNDI tree to reflect current deployments of clustered objects.
    • Cluster heartbeats — Each WebLogic Server instance in a cluster uses multicast to broadcast regular "heartbeat" messages that advertise its availability. By monitoring heartbeat messages, server instances in a cluster determine when a server instance has failed. (Clustered server instances also monitor IP sockets as a more immediate method of determining when a server instance has failed.)
    • Clusters with many nodes — Multicast communication is the option of choice for clusters with many nodes.

    b) Using IP Unicast: WebLogic Server provides an alternative to using multicast to handle cluster messaging and communications. Unicast configuration is much easier because it does not require cross network configuration and the additional setup that multicast requires.

    For further details, refer to the following excellent document from Oracle Understanding WebLogic Server Clustering