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Server Load Balancing Methods
Published: Tuesday, May 18, 2004
Methods of load balancing
There are various ways in which load balancing can be achieved. The deciding factors for choosing one over the other depends on the requirement, available features, complexity of implementation, and cost. For example, using a hardware load balancing equipment is very costly compared to the software version.- 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 cluser. The details on the implementation is discussed here.
Pros: Very simple, inexpensive and easy to implement.
Cons: 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.
- 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 comes for a much higher cost.
Pros: Uses circuit level network gateway to route traffic.
Cons: Higher costs compared to software versions.
- Software Load Balancing
Most commonly used load balancers are software based, and often comes as an integrated component of expensive web server and application server software packages.
Pros: Cheaper than hardware load balancers. More configurable based on requirements. Can incorporate intelligent routing based on multiple input parameters.
Cons: Need to provide additional hardware to isolate the load balancer.
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Server Load Balancing: Algorithms
