Tuesday, April 28, 2009

Load Balancer Overview

What is Load Balancer in Oracle Applications 11i ?
As name suggest its used to balance load on oracle applications, so lets say you initially sized (How to size server configuration in your apps 11i Instance during Implementation coming soon..) your server for 100 concurrent users & now additional 90 users started using your system , you can configure one more Application Tier node & distribute load of 190 users across two application tier node by configuring load balancer (Currently I am discussing only about Application Tier & once you are comfortable with Middle Tier I'll discuss on database tier)

Why I need load balancer in Apps 11 ?
Is Increased load only reason for introducing load balancer in Apps 11i , No not at all . There are other reasons as well like (These are more advanced reasons & if you don't understand don't worry read it for understanding purpose at this minute)
- You want to Hide Server Name so instead of users accessing it via http://hostname:port you want users to access by http://somefancyname.com use load balancer (I know you can do this by various other ways as well like reverse proxy, via dns ..)
- You want on some node only web server & some both form server & web server

and there can lot of other reason why you need load balancer (May be you want to put it in your CV that you know how to configure load balancer, I know this is stupid reason :) )

What is Role of Load balancer in Oracle Application 11i ?
Usually load balancer act as mediator in passing your request to respective Middle Tiers (Usually web server ), so lets say you have configured load balancer in front of two middle tier which are part of your Applications 11i lets call them MT1 & MT2 . Load balancer will accept client's request and pass on to MT1 & MT2 ( round robin or the way you have configured load balancer, you here is Unix Administrators)

What are different kind of load balancer ?
Session Persistent - These kind of load balancers assign request from a client to same Application Tier. so lets say user1 tried connecting applications via load balancer and LB sent that request to MT1 then in future LB will send requests from user1 always to MT1 for time being specified in session persistence duration parameter specified in LB configuration or till user logs out from Applications. This property is called as Stickness or sticky Bit

Non Session Persistent - These kind assign request to MT in round robin way so lets assume user1 requested for login page , LB sends this request to MT1 then user1 again clicked on user responsibility and this time LB sent request from user1 to second middle tier i.e. MT2

Other types of LB, I am not discussing here as these are not required at this minute

What all different kind of load balancing options available in Oracle 11i ?
DNS Level Load Balancing ( Check image at top , this represent DNS level LB)
HTTP Layer Load balancing (You need hardware load balancer which accepts http requests)
Jserv Load balancing (This is example of software load balancer, via mod_oprocmgr Process Manager Module)
Forms level load balancing - Jserv load balancing via forms servlets (More coming in future) , forms metrics server adfmsctl.sh

How to configure Load Balancer in Oracle Apps 11i ?
Coming in Next post...

Things which need Extra Attention while Configuring Load Balancer in front of Oracle Apps Web Server
Coming in Next post...

How to confirm if load balancer is sending requests to all nodes which are configured for load balancer ?
Coming in Next post...

Where to find documents to configure Load Balancer ?
Coming in Next post...

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