Clustering
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This document discusses WebLogic server domains, clusters, and high availability configurations. It defines domains as logically related groups of WebLogic servers managed from a single configuration, and notes they contain servers and server clusters. It describes the administration server's role in central configuration and deployment, and managed servers which host applications. It explains how server clusters provide scalability and high availability through load balancing, failover, and replication across multiple servers.
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Clustering
- 1. Clustering -Vijay Amrit Raj Sharma Scandihealth 1
- 2. Application Server as Middleware App Server is referred to as middleware because it is responsible for connecting the client with the database servers and for serving the information contained in the databases/Infomraition Systems. Scandihealth 2
- 3. Weblogic Setup - Production Scandihealth 3
- 4. Domain • What is it? – a logically related group of WebLogic Server instances that you manage from a single set of configuration artifacts. • What’s in a domain? – Servers – Clusters of servers config.xml Scandihealth 4
- 5. Administration Server Managed Servers • What is it? – Central configuration controller for the entire domain • What else does it do? Admin Server – Hosts the Administration Console config.xml – Enables you to start and stop servers from a central location – Enables you to migrate servers and services within the domain – Enables you to deploy applications within the domain • Guidelines: – There must be exactly one* Administration Admin Console Server in domain – An Administration Server controls only one domain. – For production use, we recommend not hosting application logic or resources on the Administration Server *The Administration Server does not need to run at all times, but is required for making configuration and deployment changes to a running domain. Scandihealth 5
- 6. Managed Server • What is it? JNDI – A running instance that hosts JMS Queue applications and resources needed by those applications - The real work JDBC Pool horses in a WebLogic domain – Each Managed Server is independent of all other Managed Servers in the domain (unless they are in a cluster, defined later) – You can have as many Managed Servers in a domain as you need – Individual Managed Servers are typically added for capacity and application isolation Scandihealth 6
- 7. Application Failover Simply put, failover means that when an application component doing a particular “job”—some set of processing tasks—becomes unavailable for any reason, a copy of the failed object finishes the job • For the new object to be able to take over for the failed object: • There must be a copy of the failed object available to take over the job. • There must be information, available to other objects and the program that manages failover, defining the location and operational status of all objects—so that it can be determined that the first object failed before finishing its job • WebLogic Server uses standards-based communication techniques and facilities— including IP sockets and the Java Naming and Directory Interface (JNDI)—to share and maintain information about the availability of objects in a cluster • Information about what has been done on a job is called state. WebLogic Server maintains information about state using techniques called session replication and replica-aware stubs Scandihealth 7
- 8. Load Balancing in a Cluster Load balancing is the even distribution of jobs and associated communications across the computing and networking resources in your environment. For load balancing to occur: • There must be multiple copies of an object that can do a particular job. • Information about the location and operational status of all objects must be available WebLogic Server shares and maintains the availability and location of deployed objects using unicast, IP sockets, and JNDI • For JSPs and Servlets: load balancing is external – Web server proxy plug-in (round robin): – HTTP Proxy servlet (i.e., using WLS as a load balancer) – 3rd party hw or sw load balancer – Load balancing algorithms: Round robin, weighted, random, server affinity Scandihealth 8
- 9. Weblogic Cluster • A WebLogic cluster is a collection of servers that coordinate their actions to provide scalable and highly-available services • Scalable services – Add or remove servers as needed – Load balance requests – Concentrate communication • Highly-available services – No single point of failure – Failover requests – Scalability: through parallelism – Reliability/Availability: through replication and redundancy Scandihealth 9
- 10. Cluster Guidelines • All servers in a cluster must also be in the same domain. • All servers within a cluster must be at the same Maintenance Pack level. • Clustered servers can be on the same or different machines. • You can have multiple clusters in a domain. Scandihealth 10
- 11. Communication in a Cluster • Peer to Peer using Sockets - used for: – Accessing non-clustered objects deployed to another clustered server instance on a different machine. – Replicating HTTP session states and stateful session EJB states between a primary and secondary server instance. – Accessing clustered objects that reside on a remote server instance. • Multicast - used for: – Cluster-wide JNDI updates – Heartbeats • Cluster-wide JNDI tree – Lists local resources and resources available throughout the cluster – List is maintained on all servers in the cluster Scandihealth 11
- 12. Configuring for High Availability • Clustered servers for HA and scalability A1 A1 A1 A1 • All managed servers in the same cluster A2 A2 A2 A2 are on different machines, although machines are frequently shared Admin Server Managed Server Node Manager Scandihealth 12
- 13. HttpClusterServlet • WebLogic provides a rudimentary software load balancer, the HttpClusterServlet, which round-robins HTTP requests through all the available servers in the cluster. • A hardware solution typically includes additional logic to monitor the load on individual machines and distribute the requests accordingly. <!-- web.xml entry --> <init-param> <param-name>WebLogicCluster</param-name> <param-value> 10.0.10.10:7001:7002|10.0.10.10:7003:7004 </param-value> </init-param Scandihealth 13
- 14. Recommended Architecture Scandihealth 14
Editor's Notes
- #4: The following figure shows a typical production environment that contains an Administration Server and multiple WebLogic Servers instances. When you start the server instances in such a domain, the Administration Server is started first. As each additional server instance is started, it contacts the Administration Server for its configuration information. In this way, the Administration Server operates as the central control entity for the configuration of the entire domain
- #5: You can use a variety of criteria for organizing WebLogic Server instances into domains. For instance, you might choose to allocate resources to multiple domains based on logical divisions of the hosted application, geographical considerations, or the number or complexity of the resources under management. For additional information about domains see Understanding Domain Configuration. Domain Restrictions In designing your domain configuration, note the following restrictions: Each domain requires its own Administration Server for performing management activities. When you use the Administration Console to perform management and monitoring tasks, you can switch back and forth between domains, but in doing so, you are connecting to different Administration Servers. All Managed Servers in a cluster must reside in the same domain; you cannot split a cluster over multiple domains. All Managed Servers in a domain must run the same version of the WebLogic Server software. The Administration Server may run either the same version as the Managed Servers in the domain, or a later service pack. If you have created multiple domains, each domain must reference its own database schema. You cannot share a configured resource or subsystem between domains. For example, if you create a JDBC data source in one domain, you cannot use it with a Managed Server or cluster in another domain. Instead, you must create a similar data source in the second domain. Furthermore, two or more system resources cannot have the same name.
- #6: Do you need to explicitly configure the admin server? Administration Server The Administration Server operates as the central control entity for the configuration of the entire domain. It maintains the domain's configuration documents and distributes changes in the configuration documents to Managed Servers. You can also use the Administration Server as a central location from which to monitor all resources in a domain. To interact with the Administration Server, you can use the Administration Console, WLST, or create your own JMX client. See Summary of System Administration Tools and APIs in Overview of WebLogic Server System Administration to modify the domain's configuration. Each WebLogic Server domain must have one server instance that acts as the Administration Server. In each domain, one WebLogic Server instance acts as the Administration Server—the server instance which configures, manages, and monitors all other server instances and resources in the domain. Each Administration Server manages one domain only. If a domain contains multiple clusters, each cluster in the domain has the same Administration Server. More Thoughts: -MSI Mode -Disabling the Admin Console
- #7: 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. Managed Servers can use the following resources: Machine definitions that identify a particular, physical piece of hardware. A machine definition is used to associate a computer with the Managed Servers it hosts. This information is used by Node Manager in restarting a failed Managed Server, and by a clustered Managed Server in selecting the best location for storing replicated session data. For more information about Node Manager, see Using Node Manager to Control Servers in Managing Server Startup and Shutdown . Network channels that define default ports, protocols, and protocol settings that a Managed Server uses to communicate with clients. After creating a network channel, you can assign it to any number of Managed Servers and clusters in the domain. For more information, see Configuring Network Resources in Configuring WebLogic Server Environments . Virtual hosting, which defines a set of host names to which WebLogic Server instances (servers) or clusters respond. When you use virtual hosting, you use DNS to specify one or more host names that map to the IP address of a server or cluster. You also specify which Web applications are served by each virtual host. JNDI Naming services as a means for locating objects over the network. EJB EJB provides a mechanism that contains business logic for building reusable Java components. It also helps users build component-based distributed applications JMS It aids communication between applications with the help of message exchanges.
- #8: WebLogic provides a rudimentary software load balancer, the HttpClusterServlet, which round-robins HTTP requests through all the available servers in the cluster. A hardware solution typically includes additional logic to monitor the load on individual machines and distribute the requests accordingly
- #9: WebLogic provides a rudimentary software load balancer, the HttpClusterServlet, which round-robins HTTP requests through all the available servers in the cluster. A hardware solution typically includes additional logic to monitor the load on individual machines and distribute the requests accordingly