Load Balancers distribute incoming network traffic across multiple servers to ensure optimal resource utilization, minimize response time, and prevent server overload. When it comes to load balancing, three primary types exist: software load balancers, hardware load balancers, and virtual load balancers.

1. Types of Load Balancer – Based on Configurations

1.1. Software Load Balancers

Software load balancers are applications or components that run on general-purpose servers. They are implemented in software, making them flexible and adaptable to various environments.

• The application chooses the first one in the list and requests data from the server. 
• If any failure occurs persistently (after a configurable number of retries) and the server becomes unavailable, it discards that server and chooses the other one from the list to continue the process. 
• This is one of the cheapest ways to implement load balancing. 

1.2. Hardware Load Balancers

As the name suggests we use a physical appliance to distribute the traffic across the cluster of network servers. These load balancers are also known as Layer 4-7 Routers and these are capable of handling all kinds of HTTP, HTTPS, TCP, and UDP traffic. 

Hardware load balancers are dedicated devices designed for the sole purpose of managing network traffic. They often come as standalone appliances or modules within networking hardware.

• HLBs can handle a large volume of traffic but it comes with a hefty price tag and it also has limited flexibility.
• If any of the servers don’t produce the desired response,  it immediately stops sending the traffic to the servers. 
• These load balancers are expensive to acquire and configure, which is the reason a lot of service providers use them only as the first entry point for user requests.
• Later the internal software load balancers are used to redirect the data behind the infrastructure wall. 

1.3. Virtual Load Balancers

A virtual load balancer is a type of load balancing solution implemented as a virtual machine (VM) or software instance within a virtualized environment ,such as data centers utilizing virtualization technologies like VMware, Hyper-V, or KVM. It plays a crucial role in distributing incoming network traffic across multiple servers or resources to ensure efficient utilization of resources, improve response times, and prevent server overload.

2. Types of Load Balancer – Based on Functions

 2.1. Layer 4 (L4) Load Balancer/Network Load Balancer

Layer-4 load balancers operate at the transport layer of the OSI model. They make forwarding decisions based on information available in network layer protocols (such as IP addresses and port numbers).

Key Features of Layer-4(L4) Load Balancer:

• Transport Layer: Operates at the transport layer (TCP/UDP).
• Basic Load Balancing: Distributes traffic based on IP addresses and port numbers.
• Efficiency: Faster processing as it doesn’t inspect the content of the data packets.
• Network Address Translation (NAT): Can perform basic NAT to hide server addresses.

2.2. Layer 7 (L7) Load Balancer/Application Load Balancer

Layer-7 load balancers operate at the application layer of the OSI model. They can make load balancing decisions based on content, including information such as URLs, HTTP headers, or cookies.

Key Features of Layer-7(L7) Load Balancer

• Application Layer: Operates at the application layer (HTTP, HTTPS).
• Content-Based Routing: Distributes traffic based on content-specific information.
• Advanced Routing: Can make intelligent routing decisions based on application-specific data.
• SSL Termination: Capable of terminating SSL connections.

2.3. GSLB (Global Server Load Balancer) a.k.a. Multi-site Load Balancer

GSLB stands for Global Server Load Balancer. This type of load balancer goes beyond the traditional local load balancing and is designed for distributing traffic across multiple data centers or geographically distributed servers.

• A GSLB load balancer is concerned with global or wide-area load balancing.
• It takes into account factors such as server proximity, server health, and geographic location to intelligently distribute traffic across multiple locations.