What does a Load Balancer do?
Load balancers are an integral part of today’s Web infrastructure. They’re also complex and under documented pieces of hardware.
Today’s Web sites are often beasts. Every component must work together to create a site that is greater than the sum of its parts.
In the most basic sense possible, the internet works like this:
The Internet traffic comes into a Router, which passes that traffic through a Firewall to a Load Balancer, which distributes the traffic to a Web Server, which passes information along to an Application Server, and then the Application Server is connected to a Database Server, which is connected to….. Well, you get the picture.
If one component or piece of this passing data back and forth process fails, it can take down the entire site. (It’s like what happens when one of the Holiday lights goes out, the whole string goes out!)
Load balancing, in regards to dedicated hosting, is often used by high traffic sites to spread traffic across multiple servers that have identical content. In addition to diverting traffic to multiple servers for high traffic sites, it can also be very effective as a fail over solution if it is mission critical that your website be online at all times.
How on earth does it accomplish this feat?
Simple answer… A busy web site typically employs two or more Web servers in a load-balanced scheme. If one server starts to get swamped, requests are then forwarded to another server with more capacity. Load balancing is therefore usually a service that is employed on more sophisticated site deployments.
In slightly more technical terms… A Load Balancer shows a single, virtual server address to the outside world, which maps to the addresses of each server within the cluster. When a request comes to the Load Balancer, it rewrites the request’s header to point to other machines in the cluster. If a machine is removed from the cluster, the request does not run the risk of hitting a dead server, since all of the machines in the cluster appear to have the same IP address. This address remains the same even if a node in the cluster is down. Moreover, cached DNS entries around the Internet are not a problem. When a response is returned, the client sees it coming from the hardware Load Balancer machine. In other words, the client is dealing with a single machine, the hardware Load Balancer.
Methods of load balancing
1. Round Robin DNS Load Balancing
The in-built round-robin feature of BIND of a DNS server can be used to load balance multiple web servers. It is one of the early adopted load balancing techniques to cycle through the IP addresses corresponding to a group of servers in a cluster.
- Very simple, inexpensive and easy to implement.
- The DNS server does not have any knowledge of the server availability and will continue to point to an unavailable server.
- It can only differentiate by IP address, but not by server port. The IP address can also be cached by other name servers and requests may not be sent to the load balancing DNS server.
Software Load Balancing
Most commonly used load balancers are software based, and often come as an integrated component of expensive web server and application server software packages.
- Cheaper than hardware load balancers. More configurable based on requirements.
- Can incorporate intelligent routing based on multiple input parameters.
- Need to provide additional hardware to isolate the load balancer.
- Can be difficult to maintain. Requires supervision.
Hardware Load Balancing
Hardware load balancers can route TCP/IP packets to various servers in a cluster. These types of load balancers are often found to provide a robust topology with high availability, but come with a much higher cost.
- Uses circuit level network gateway to route traffic.
- Higher costs compared to software versions.
The Benefits of Hardware Load Balancing:
Load Balancers Improve:
>> Server availability by avoiding overload of individual servers and monitoring effectiveness and responsiveness of each node in a cluster
>> Server efficiency by relieving servers of resource-intensive housekeeping functions such as SSL encryption and decryption.
>> Customer and end-user responsiveness by ensuring that each new visitor to a web site or application is connected to the server which will handle their request fastest.
>> Network security and stability by eliminating single points of failure and downtime for server farm maintenance or upgrade
>> Network and website management by eliminating failed connections, improving response time and availability, and securing stable SSL connections communications.
>> Ecommerce satisfaction by ensuring high responsiveness and session/account persistence over multiple customer connections to the site
>> Traffic management by routing different traffic types based on user-defined criteria.
>> Web-site performance by eliminating server failures and overload, adding backup and failover capabilities, and maximizing use of server resources
>> Business continuity by eliminating many key initiators of website failure
>> Resource use by gaining up to 25% improved use of existing servers
Test Results: Load Balancing
See here a set of test results that clearly show the benefit of a Load Balanced solution when testing with different user sets, and different numbers of transactions. You can clearly see what Load Balancing can do for sites that have a large amount of traffic.
Test conducted by Sean Doherty who is a senior technology editor and lawyer based at Syracuse University Real-World Labs®
We currently offer two Coyote Point Load Balancers, both are currently priced the same. We select the Load Balancer that our customer needs, thus providing the best possible quality of hardware every time.
In this comparison of the two Coyote Point Load Balancers we offer, please see the differences between the two. As you can clearly see, they are certainly different as far as what they are capable of. The 350 is a much more robust version, but unless you are running a lot of traffic through the Balancer, is all that robustness really required? Sometimes it may be better to just utilize the smaller version.
The bottom line here is that although a Load Balancer comes with a hefty price tag, in some cases it is just a necessary thing. Some websites simply cannot maintain their traffic without additional help. There are other solutions, but in some cases, the hardware piece of the equation is just the right one. In those cases, we are wise to have an offering for our customers that not only makes sense to them, but also makes sense to our bottom line.
Load Balancers are traditionally very expensive, but in my research I found that not only do the Coyote versions stand up to the competition, they are also one of the most cost effective versions out there. Good choice Layered Technologies!
~ Hallie Weaver, LT Account Manager, firstname.lastname@example.org >>