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HostVentures provides load balancing consulting, implementation and support. Our experience in the field is unmatched, ranging from Fortune 100 consulting, to helping small businesses grow, to supporting configurations with over a million unique visitors per day. Please contact us for more information.
Load Balancing is generally done to achieve scalability, improved performance, as well as high-availability and failover. There are multitudes of methods for spreading load and they are not all created equal as many do not incorporate failover or redirection of traffic away from failed servers or points of presence to functinal ones.
Here are some alternate methods for performing load balancing in order from highest to lowest availability characteristics:
- Global Load Balancing
Multiple globally dispersed points of presence require load distribution at the DNS (Domain Naming Service) level and need to incorporate active monitoring and communication between DNS servers to provide effective failover. Note that simple DNS services with multiple locator (A) records do not exhibit any failover characteristics. Many network load balancing appliances incorporate advanced global load balancing DNS and monitoring features.
- Load Balancing Appliance
Use of an appliance such as Cisco CSS, Alteon, Foundry Networks to provide a "virtual ip address" that is services by 2 or more servers on a private network subnet, provides seamless and instant failover, scalability, as well as increased security. This scheme can be combined with Global Load Balancing to enhance each point of presence with additional failover using network appliances.
- Linux Virtual Server
The linux virtual server project serves the same function as mainstream load balancing appliances. It is an open source product which lacks standard commercial support and sits a level below commercial load balancing appliances in terms of capability and performance.
- DNS Methods
When a DNS server, such as BIND, is running on each network in a load balanced configuration one can obtain a level of network failover since when one network is unavailable, the DNS server cannot respond to requests that would direct traffic to the unavailable network. However, this does not provide a high degree of availability since the individual servers can fail for many reasons, including hardware, operating system, application and database problems.
- Miscelaneous
In all probability, an infinite number of schemes for load balancing can be devised. Various application level methods for example can provide load distribution functionality. Such methods are not standard and while sometimes useful are not the preferred first choice for high-availability and load balancing approaches.