Saturday, October 15, 2016

Oracle WebLogic Server - Part 1 - Main components and their relationship

In this post series, I am planning to write about the important things I learned about the WebLogic server during past few years (specially about version 10.3.6). Main purpose of these posts is to keep it as a future reference.

The WebLogic Server is an "application server" developed by the Oracle Corporation, and it supports many powerful features such as high availability, scalability, high performance, reliability, etc.

 The WebLogic Server has following main components.

Domain

A WebLogic domain is a logically related group of WebLogic server resources. A WebLogic domain has a special server instance known as “Admin Server”, and zero or more server instances known as “managed servers”.

All WebLogic server instances in a WebLogic domain must have same WebLogic major and minor version. The server instances in a WebLogic domain can be distributed through out several machines.

Admin Server

This is the component which helps the configuration, management, and monitoring of the servers and resources in the whole WebLogic Server domain. You can access the Admin Server through,
  • The "WebLogic Admin Console" web application Or
  • An UNIX shell like command line interface known as "WLST" Or
  • Through JMX API
 All the configurations settings related to the Admin Server, managed servers, clusters, and machines are stored and managed in the Admin Server, mainly in a file named config.xml.

Using Admin Server, You can
  • Start/stop managed servers,
  • Deploy/update/delete applications,
  • Update settings of managed servers/admin server/cluster/etc.,
  • Create/edit/delete more managed servers/clusters/machines etc.
  • Monitor health of the servers.

Managed Servers

In a WebLogic domain, you can have zero or more servers known as "managed servers".  These are separate JVM processes.

A "managed server" is the server process where usually you deploy your application. Although it is possible to deploy an application in Admin Server, it is not the intended usage of the Admin Server.

A “managed server” can be a part of WebLogic cluster, but it is not mandatory.

Clusters

A cluster is a set of managed servers grouped to achieve Scalability (Horizontal scalability) and High Availability. A cluster appears to the client as a single WebLogic server instance (when client access the cluster through a load balancer or use the cluster address to connect to the EJBs in the cluster). All managed server instances in a cluster must belong to the same WebLogic domain. You can create a WebLogic cluster distributed in one or more server machines.

WebLogic cluster has following capabilities in order to achieve the Scalability and High Availability.
  • Application Fail Over Protection
  • Load Balancing
  • Supporting automatic and manual migration of resources between servers in the cluster.

Machines

A “machine” in WebLogic is a logical representation of a physical machine or a virtual machine, which contains one or more WebLogic server instances (Admin Server or managed servers).

In each machine, there is a special process known as “Node Manager” in order for Admin Console to start/stop “managed server” instances in the respective machine, without actually login to that machine. “Machine” configuration includes the listen address and the port of the Node Manager of the respective “machine”.

Machine Types:

  • Unix
  • Virtual
  • Other

Node Manager

In WebLogic Server environment, the Admin Server does not connect to the managed servers directly. In each machine, a separate process named "node manager" should be running for helping this purpose.

A "node manager" process is necessary for managing server instances through Admin Server or similar remote client and to support restarting of failed server instances.

But it is not mandatory to have a node manager process if you do not want above features.

Purpose of Node Manager Process:

  • Allow to stop/start/restart WebLogic server instances in the machine which has the Node Manager process from a remote/local machine (mainly, but not necessarily from the Admin Server)
    • If a server instance started using a node manager fails and AutoRestart attribute of the server set to true, the node manager automatically restart that server instance.
  • Allow monitoring of the health status of WebLogic servers from a remote machine. (mainly, but not necessarily from the Admin Server)
  • Retrieve server logs and node manager logs.

(In the above diagram, Admin Server can be at only one location depicted above in a given domain, not in the both places at once).

Please see my next blog post "Oracle WebLogic Server - Part 2 - Node Manager and its interaction with WebLogic Server instances" for more information about the node manager and its interaction with other components.

References:



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