WebLogic Domains

Overview
This topic introduces the WebLogic Domains, Basic Infrastructure components in a domain, domain constraints, domain creation types.

It includes the following  sections:

• Introduction to WebLogic Domain
• Basic WebLogic Domain Components
• Domain Constraints
• Types of Domain Creation

Introduction to WebLogic Domain
It is the basic administrative unit of WebLogic Server. It consists of one or more WebLogic Server instances, and resources & services which are logically related and that are managed by a single administration unit.

Basic WebLogic Domain Components
A WebLogic Domain contains the below basic components

• Administration Server
• Managed Server
• Cluster
• Node Manager

In addition to above components, a domain also contains the resources and services required by Managed Servers and hosted applications deployed in the domain.

Resources and Services

Examples of these resources and services include:

• Application Deployments
• JDBC data sources
• JMS Messaging Services
• security options
• Persistent Stores
• Startup classes
• Diagnostics and monitoring services etc.,

The domain also includes information about the networked computer environment in which the domain runs, such as:

Machine definitions: It 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. 

Network channels, an optional resource that can be used to define default ports, protocols, and protocol settings. After creating a network channel, you can assign it to any number of Managed Servers and clusters in the domain.

Now we will discuss more about basic domain components.

Administration Server
It is a WebLogic Server Instance runs in JVM which is used to launch Administration Console.

Admin Server is used for

1. Creation & Configuration of Managed Servers, Clusters, Resources & Services
2. Monitoring the health of the domain (ex:monitoring WebLogic Servers, Services etc.,)
3. Controlling theWebLogic Domain (starting/stopping servers, services etc.,)
4. Deploying the applications and other resources,

 A domain contains only one Administration Server.

Managed Server
It is a WebLogic Server Instance runs in JVM which is used to hosts the application

A domain contains zero or many manged servers. If there is no manged server in the domain, the administration server also plays the role of managed server

Cluster
It is a group of WebLogic managed servers instances which are working together to provide High Availability, Scalability. A domain contains zero or many clusters.

Production environments contains two or more of Managed Servers as a cluster to have the increased application performance, high availability

Clustering allows multiple Managed Servers to operate as a single unit to host applications and resources.

Node Manager
It is a WebLogic utility which is used to control the WebLogic Server Instances remotely.

Domain Constraints 
In creating your domain configuration, note the following restrictions.

• Each domain requires its own Administration Server for performing management activities. 
• 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.
• You can not span cluster over multiple domains; All Managed Servers in a cluster must reside in the same domain.
• You cannot share a configured resource or subsystem between domains. For example, if you create a JDBC connection pool in one domain, you cannot use it with a Managed Server or cluster in another domain. 

Types of Domain Creation
You can create WebLogic domain in two ways

1. GUI Mode 
2. Console Mode

You can also use WLST to create a domain