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Web load balancing

Before you investigate web load balancing, take some time to get the facts about cost and options.

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Web load balancing

Before you investigate this method, take some time to understand the current performance of your Web site and where the current or potential bottlenecks are located.

by Johanna Ambrosio

Load balancing your Web site is something to consider whether you're selling billions of dollars' worth of goods online or are a mom-and-pop shop with a much smaller site. Load balancing basically means that you divide the amount of work that a computer has to do between two or more computers.

The key benefit is that load-balancing hardware and software allow requests for information and other "hits" to the site to be automatically redirected to a free server, thus evening out the traffic load so that visitors don't need to wait overly long for their answers.

So says Nigel Hughes, the service leader for e-commerce at Compass Management Consulting Ltd., a global firm specializing in business and IT performance improvement for Fortune 1000 organizations. Hughes, who works out of the London office of Compass, recently addressed the issues surrounding Web load balancing.

Why should companies consider load balancing?

Load balancing will allow them to increase reliability, performance and make maximum use of their current investments.

An analogy is with checkouts in a grocery store. If you are in a checkout line and can see that another checkout is free, then you would probably move across. The same applies to processing requests to a Web site. You don't want expensive server resources sitting underutilized while others are struggling to keep up with demand.

Load balancing can also go further in that it is able to use multiple checkouts per person. So where the family of eight has a month's worth of groceries in one cart, load balancing can break up the contents of the cart and distribute it across several checkouts, thus speeding up the average service time.

Does load balancing work?

The simple answer is yes, but care must be taken in choosing an appropriate solution in terms of cost and performance. Best practice states that you ensure that there is redundancy built into your load-balancing solution. The last thing you want to do is introduce a high-cost, complex solution that acts as a single point of failure.

The key characteristics of a robust solution are:

-The load should be dynamically speeded among server resources, giving clients best possible performance.

-The service should remain available during planned and unplanned downtime.

-You should be able to increase your capacity without disruption to service.

Before investigating load balancing, take some time to understand the current performance of your Web site and where the current or potential bottlenecks are located. Typically, bottlenecks include server utilization and network bandwidth.

Next, look to the future and make some estimates on growth.

Finally, have a look at your budget.

What are the various load balancing techniques?

There are a number of techniques, and they generally fall into the following three categories:

-Simple routing, or DNS round robin

Simple routing is when a list of servers is maintained and requests are routed to a specific server based on the address requested. DNS round robin adds to this by maintaining a similar list but when a request comes in it is assigned to the next server on the list until the end of the list is reached. The next request is then assigned to the first server again and so on. The advantage of these methods is simplicity, and as long as you either have relatively light or consistent traffic requests coming in it works very well. There is no prioritization of traffic. More complex or more important requests receive equal priority with all other requests.

-More complex routing algorithms

Requests can be distributed based on performance of the servers (fastest servers get more load), the type of server (i.e. this request needs something special that's only available on particular server) or by customer priority. This works well for heavy loads, but there can come a point when a threshold is reached where the load balancing solution becomes the bottleneck.

-Intelligent routing

This balances load based on the content of the request. It can also handle session failures so that orders, for example, can be redirected transparently in the event of failure.

What are the vendors offering?

Vendors offer two types of solutions:

-Dedicated load balancing devices: expensive, suitable for the enterprise, out of the box with little configuration necessary, very fast and very reliable. Upgrades are limited because they require new or upgraded hardware.

-Server based: software is installed directly on either a dedicated server or application servers. Lower upfront costs, flexibility and fine-tuning, but with steep learning curve and additional administration cost. Upgrades are generally cheaper and simpler, due to how only the software needs to be upgraded.

What options exist outside of load balancing for managing heavy Web traffic?

You can outsource; increase server capacity; improve the design of your site; use RAID hardware; provide bandwidth on demand to handle expected peaks, and partition the load by the servers.

How might one go about making a decision?

You should make sure that the solution you choose can handle monitoring, reporting and accounting. The solution should be able to monitor traffic analysis such as response times, bandwidth utilization and errors. It should also have accounting features to let you look at traffic by groups of users and content accessed. Also consider the ongoing cost of administration as well as lease/purchase cost. Find out what others have done, and make sure it's scalable so it fits in with your future growth plans. Leased solutions are often good from this perspective.

Also factor in the cost of not doing it. The magic 8-second figure is often cited: If a page load takes longer than 8 seconds customers will go somewhere else. Load balancing can considerably improve response time, especially during peak activity.

Finally, load balancing is a technical and complex subject with a multitude of solutions. But also remain focused on the key aspects: understand what you are trying to do, what you will need to do in the future, what skills you have access to and what your budget is. Don't get carried away with the wondrous technical possibilities that exist. As Einstein said, "Make it as simple as possible, but no simpler."

Ambrosio is a freelance writer in Marlborough, Mass.; write her at jambrosio@mediaone.net

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