Application Server 10g Load balancing.

Documents Created by             : Bharat Gali

Created date                            : 01-Feb-2006

Application Server Version        :10.1.2.0.2

Last Revised                             :30-Apr-2006

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This document focused on Load balancing concepts  with some examples that I implemented with some of my clients and did n't cover the basic concepts of Application server. For more information Application server and its concepts please refer Oracle site.

1) Process death detection and automatic restart.

• OPMN tracks any application server components (Forms,Report,Portal etc etc)   if it is register with it. OPMN continuous pings its registered components and writes to logs about the state and status.

• OPMN detects Oracle Application Server processes that are down or unreachable, it automatically restarts them.

        Example OPMN command

        $ORACLE_HOME/opmn/bin  opmnctl status

2)Active-Active Load balancing.

•  Two or more Oracle Application Server instances are configured to serve the same workload. These instances can run on the same machine or on different machines. The instances are front-ended by an external load balancer, which directs requests to any of the active instances. Instead of an external load balancer, you can also run a software load balancer to distribute the requests. In production environment, however, a hardware load balancer is recommended.

• The instances need to serve the same workload or applications. Some configuration properties should have similar values across instances so that the instances can deliver the same reply to the same request. Other configuration properties may be instance-specific, such as local host name information.
• If you make a configuration change to one instance, you should also make the same change to the other instances in the active-active topology.

• If one Oracle Application Server instance in an active-active topology fails, the other instances in the cluster continue to serve requests. The load balancer directs requests only to instances that are alive.

Advantages of an active-active topology:

• Increased availability
• An active-active topology is a redundant configuration. Loss of one instance can be tolerated because other instance can continue to serve the same requests.
• Increased scalability and performance
• Multiple identically-configured instances provide the capability to share a workload among different machines and processes. You can scale the topology by adding new instances as the number of requests increase.

Active-Active Topologies Implementation Requirements

• Active-active topologies use a load balancer to direct requests to one of the Oracle Application Server instances in the topology. In other words, the Oracle Application Server instances are fronted by the load balancer. You configure the load balancer with virtual server names for HTTP and HTTPS traffic. Clients use the virtual server names in their requests. The load balancer directs requests to an available Oracle Application Server instance.

Run OC4J instances on multiple nodes.

•  OC4J clustering is very important in application server load balancing to achieve maximum service availability. Below link provides implementation techniques of OC4J clustering

       Click here for implementation techniques of OC4J clustering with Examples

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High Availability Model1 Via Web cache As Shown in the above figure.

• Hardware load balancer is connected to 2 web cache servers

       1) Web Cache1

       2) Web Cache2.

• Based on Availability and load web cache servers direct the request to either M1 OR M2 SERVER.

• Middle Tier servers M1 and M2 are connected to two infra structure services which share common OID repository.  

Disadvantages of this model

• There is no redirection of the session for OCJ4 with this model. For examples Some one already connected to OCJ4 application (Forms, reports and ETC) and there is a failure in the service. With this model there is not re direction mechanism to the second OC4J. This can be achieved thought OC4J clustering. Which is shown in the next model

High Availability Model2

• The above model is same as model 1 except it is having OC4J clustering. OC4J clustering can handing the re-directions which are failure in the middle

Example

If the application is connect via OC4J 1 and failed. With the OC4J clustering it is still possible to transfer to second OC4J.

Below is the link for OC4J clustering implementation.

OCJ4 clustering.

Above model there are no Web cache servers. Load balancing routers is directly connected to OC4J Servers. And only one infrastructure instance is running. Normally the failure in infrastructure are very less compare to the failures of middle tier.  This is the typical model which is implemented lot of place.