Invite suggestions and guidelines for Load balancing of asp .net application.

Question

Hi,

I have an asp .net 2.0 web application which is a online survey system.At times it has huge number of users and the application go slow.

I wanted to do load balancing for the web application which runs in a single server now.

Will anyone suggest me...

a) In what all scenarios i should consider load balancing to my application?

b) what type of applications need load balancing?

c) what is the pros and cons of load balancing?

d) what is the guidelines for devoloping applications which targets load balancing,

e) At max how many number of concurrent users can access web application without load balncing without affecting performance much?

In my case application is already devoloped.What all the areas i should make changes to prepare it for load balancing.

thanks in advance

SC

Answer 1

a) In what all scenarios i should consider load balancing to my application?

In any scenario when your current server can no longer handle the load by itself. There are two kinds of scaling, vertical (buy a better server) or horizontal (add more servers). Load balancing is a form of horizontal scaling, and typically gives you more bang for your buck, but is also much harder to set up.

b) what type of applications need load balancing?

Pretty much the same answer here as with a.

c) what is the pros and cons of load balancing?

Pro is that it lets you scale. Cons are that it introduces unique issues.

d) what is the guidelines for devoloping applications which targets load balancing,

The big one is session. Session state by default is stored in proc, which means that it only exists on the one server. If the user has the potential of being bounced across different servers, they will lose their session. I would recommend reading up on it here (the way you probably want to go is either dont use session, or use state server)

e) At max how many number of concurrent users can access web application without load balncing without affecting performance much?

Completely depends on your server hardware and your application requirements. I believe there are 5 asp worker processes per core, so that is one consideration right off the bat. There is also RAM usage to consider.

Answer 2

First you need to ensure that you know where the bottleneck to performance is.

• If you can focus first on getting the total round trip time for each user's page load down then you will be able to handle more users.

• In a case where you are bottlenecked on database calls you could setup more servers for load balancing your web application and get very little benefit.

• Is there a bandwidth issue with your webserver? Are requests for images, css and javascript files slowing down just as much as web application page_load requests?

• Ensure that you aren't storing too much data in session state. If you are storing lists or other large objects in memory you have to remember that you will be multiplying that memory usage by the number of users causing things to get out of control pretty quickly if you have 10,000 users with an active session. In some of these cases it may be preferable to move state information out to cookies that are stored by the user.

Answer 3

From my experience, the software load balancing options are limited, inconsistent and inflexible.

Of course, when developing the application, you need to ensure that your application can scale out for a web farm scenario - i.e, things like ensuring you are using a distributed cache provider, a state server etc.

The hardware based solutions will provide multiple methods of distributing loads and are very consistent. Consider options like using NLB/F5 Big-IP load balancers.

Have a look at this post from Scott as well - Old, but useful. http://www.hanselman.com/blog/LoadBalancingAndASPNET.aspx

Thanks, Anoop