Domain

A domain is the basic administration unit for WebLogic Server instances. A domain consists of one or more WebLogic Server instances (and their associated resources) that are managed with a single Administration Server. Multiple domains can be defined based on different system administrators' responsibilities, application boundaries, or geographical locations of servers. Conversely, a single domain can be used to centralize all WebLogic Server administration activities.

Each WebLogic Server domain must have one server instance that acts as the Administration Server. Administration Server can be used via the Administration Console or using the command line for configuring all other server instances and resources in the domain.

Figure 1-1 WebLogic Domain Structure

Description of "Figure 1-1 WebLogic Domain Structure"

Figure 1-2 Weblogic 12c Domain Overview

Description of "Figure 1-2 Weblogic 12c Domain Overview"

Administration Server

A domain includes one WebLogic Server instance that is configured as an Administration Server. All changes to configuration and deployment of applications are done through the Administration Server. The Administration Server provides a central point for managing the domain and providing access to the WebLogic Server administration tools.

Admin server start mode needs to be configured as Production Mode.

Managed Server

In a domain, server instances other than the Administration Server are referred to as Managed Servers. Managed servers host the components and associated resources that constitute applications—for example, JSPs and EJBs.

When a Managed Server starts up, it connects to the domain's Administration Server to obtain configuration and deployment settings. In a domain with only a single WebLogic Server instance, that single server works as both the administration server and managed server.

Node Manager

The Managed Servers in a production WebLogic Server environment are often distributed across multiple machines and geographic locations.

Node Manager is a Java utility that runs as a separate process from the WebLogic Server and allows the user to perform common operations tasks for a Managed Server, regardless of its location with respect to its Administration Server. While the use of Node Manager is optional, it provides valuable benefits if WebLogic Server environment hosts applications with high availability requirements.

If the user runs Node Manager on a machine that hosts Managed Servers, the user can start and stop the Managed Servers remotely using the Administration Console or from the command line. Node Manager can also automatically restart a Managed Server after an unexpected failure.

Machine

A machine in the Weblogic Serve context is the logical representation of the computer that hosts one or more Weblogic Server instances(servers). The Admin Server uses the machine definitions to start remote servers through the Node Managers that run on those servers. A machine could be a physical or virtual server that hosts an Admin or Managed Server that belongs to a domain.

Managed Server Cluster

Two or more Managed Servers can be configured as a WebLogic Server cluster to increase application scalability and availability. In a WebLogic Server cluster, most resources and services are deployed to each Managed Server (as opposed to a single Managed Server,) enabling failover and load balancing.

The servers within a cluster can either run on the same machine or reside in different machines. To the client, a cluster appears as a single WebLogic Server instance.

Dynamic Cluster

A dynamic cluster is any cluster that contains one or more dynamic servers. Each server in the cluster will be based upon a single shared server template. The server template allows to configure each server the same and ensures that servers do not need to be manually configured before being added to the cluster. This allows the user to easily scale up or down the number of servers in the cluster without the need for setting up each server manually. Changes made to the server template are rolled out to all servers that use that template.

The user cannot configure dynamic servers individually; there are no server instance definitions in the config.xml file when using a dynamic cluster. Therefore, the user cannot override the server template with server-specific attributes or target applications to an individual dynamic server instance.

When configuring a cluster, the user specifies the maximum number of servers expect to need at peak times. The specified number of server instances is then created, each based upon the server template. The user can then start-up however many the user needs and scales up or down over time according to needs. If the user needs additional server instances on top of the number the user originally specified, the user can increase the maximum number of servers instances (dynamic) in the dynamic cluster configuration.

Server Templates

A single server template provides the basis for the creation of dynamic servers. Using this single template provides the possibility of every member being created with the same attributes. Where some of the server-specific attributes like Servername, listen-ports, machines, etc. can be calculated based upon tokens.

The user can pre-create server templates and let Weblogic clone one when a Dynamic Cluster is created.

When none is available a server template is created with the Dynamic Cluster. The name and the listen ports are the only server template attributes that the user provides during Dynamic Cluster creation.

Figure 1-3 Simplified Configuration with Scalability and Elasticity

Description of "Figure 1-3 Simplified Configuration with Scalability and Elasticity"