What Is Load Balancer And How Does It Work

This comprehensive tutorial explains what is Load Balancer and how does it work. Understand the types, working, load balancing algorithm, etc.:

One of the key measures of success for any organization is its customer experience. It is imperative for any organization to maintain high standards of productivity and ensure that it can meet the increasing demands of its application.

In order to meet the multiplying requirements for applications and to ensure a positive customer experience, organizations need to ensure the responsiveness and availability of applications. Here comes the use of load balancers in the picture.

Load Balancers route requests from customers throughout the servers, which can fulfill such requests, thereby rendering an enhanced user experience.

What Is Load Balancer

Load Balancer

You must be thinking!! What is a Load Balancer is and how it works?

Don’t worry! Read the article to get answers to all your questions about load balancers and their types.

Let us begin.

In the simplest language, the flow of information from the server to any device such as PC, laptop, or smartphone is managed by a load balancer.

A load balancer can either be a hardware or even a software solution that aims at the efficient movement of packets through various servers and ensures that the network resources are utilized optimally and prevents overloading of the network.

For the effective functioning of any modern application or website, the load balancer is irreplaceable. These applications receive over a million requests from users and the only way that they are responsive and can return reliable results every time is when the servers are not overloaded and the load is balanced.

Traditionally, the addition of more servers was seen as a viable option, but the addition of load balancers is a far more cost-effective solution that promises a better experience for the users.

While talking about load balancers, it is also important to understand their working or functioning.

Suggested Reading =>> List of The Top Software Load Balancers 

How Does A Load Balancer Work

Load balancer plays a very important role in managing the traffic and routing it to those servers that can manage it effectively, ensuring the customer experience is not hampered. In order to keep track of the health of servers, both web servers, and backend servers, the load balancer is critical.

It routes traffic to the servers, which can handle it effectively. Thus it helps increase speed and optimum utilization of the capacity of the server to make sure none of the servers are overloaded. In case of downtime for one server, the load balancer routes the traffic to other servers.

In the event of the addition of a new server, the load balancer automatically starts sending requests to it.

When clients log onto a particular URL (abc@xyz.com), the load balancer intelligently secures the connection and directs the request to that destination server.

To sum up the functions of the load balancer, we can say:

  • It ensures the optimum distribution of client requests or network traffic to multiple servers.
  • Plays a decisive role in ensuring that requests are sent only to those servers which are online, thereby increasing availability and reliability.
  • It allows the addition and subtraction of servers based on demand and therefore provides the element of flexibility.

Working of load balancer


The benefits of a load balancer are multi-fold. Some of these benefits are mentioned below:

#1) Security: It provides a blanket of security to websites and no change is required for the application. It comes loaded with a Web Application Firewall, which secures the website against hackers. It also checks on any unauthorized access to the website by authenticating user credentials.

#2) Detection and prevention against DDoS traffic: Load balancer also identifies and protects against drop distributed denial of service, also called DDoS traffic even before it reaches the website. DDoS attacks are the most common types of threats regarding security and can be a nightmare for IT departments.

#3) Enhanced performance: Load balancers also considerably bring down the load on web servers, thereby rendering an enhanced experience for users. It is equipped with an SSL (Secure Sockets Layer) offload feature which ensures the availability of resources for the web application.

#4) Compression of traffic: Compression of traffic is yet another exciting feature of load balancer which helps to provide a greater experience for customers.

#5) Caching of traffic: It saves a copy of those elements of the website which have the highest rate of access. This helps with reduced requests to the webserver and supports faster access to content for customers.

#6) Continuity: The load balancer ensures continuous service to clients, even in situations when one server fails or is busy. The load or traffic is seamlessly redirected to other servers when a server is not functional or busy.

Deployment of load balancers can be in pairs to ensure continued load balancing in case of failure of one. This helps to ensure the continuity of the site for users and that the experience of users is not impacted.

#7) Scalability: It simplifies the process of change of infrastructure of servers without any impact on services for users. It can detect outages at a particular site and redirects user requests to another site.

#8) Auto-scaling for clouds: A load balancer is also beneficial with websites that are hosted on the cloud and require to be adjusted to accommodate variations in demand. The entire process becomes simple and does not require any changes from the client.

#9) Cost benefits: It provides the benefit of cost as it allows the addition of capacity instead of the more costly option of upgrading the existing server.

Algorithms Of Load Balancing

Now that we have understood the main function of the load balancer, i.e. to distribute requests across multiple servers, also called server farm, it is also important to know how this process of distribution works.

In order to understand this process of distribution, we must also have an insight into some of the common algorithms for load balancing. These algorithms vary in levels of complexity.

Some of these algorithms are mentioned below:

#1) Round Robin: This technique or algorithm ensures that the list of client requests is forwarded to different servers following a rotating list. While this technique is simple, it does not consider the load already on the server, thereby creating a situation of overload of a server.

#2) Least connection method: This method overcomes the drawback of Round Robin and makes an evaluation of the current levels of active requests with a server before any fresh requests are directed. Requests are sent to those servers which have the least count of active connections and deliver higher levels of performance.

#3) Least response time method: This method considers the time which is taken by a particular server to respond to a request pertaining to monitoring of health. The overall health of the server and the experience of users are directly gauged from the time taken by the server to respond to the health monitoring request.

In case a server takes a longer time, it clearly indicates the load on the server.

#4) Least bandwidth method: This algorithm is comparatively simple and takes into account the server that has the lowest or least traffic. This traffic is measured in Mbps.

#5) Least packet method: This algorithm considers the server which has the lowest number of packets received in a certain time period.

#6) Hashing method: This algorithm considers the hash of different data of the incoming packets while deciding the distribution of load to servers. This hash can include information on connection and header like IP address of the source, port number and domain name, etc. of the incoming packet.

#7) Custom load method: This method allows the load balancer to run a query to ascertain the load on individual servers. The server load of interest to the query can be defined in terms of CPU and memory consumption and the time is taken to respond, and a combination of these is used to manage the request.

With an understanding of the working and benefits and the types of algorithms used by the load balancer, it is also imperative to know the types of load balancers which is immensely helpful while making a choice.

Traditionally, load balancers were mainly hardware appliances but now, with a progression in technology, they can also be software-defined.

Types Of Load Balancers

In this section of the article, we will look at the types of load balancing.

#1) Network load balancer: Here, the process of routing is done at the transport layer and it can control millions of requests every second. As soon as a connection is accepted, it chooses a target. The default rule followed, in this case, is the hash algorithm.

Next, it tries to open a TCP connection with the target, and it sends requests. There is no change made to headers while forwarding the request.

Network load balancer

#2) Application load balancer: This type of load balancer decides on routing at the application layer (HTTP, HTTPS) and helps with path-based routing.

Requests can be routed to multiple ports on each container in the cluster. It is also capable of port mapping. At the beginning of the assignment, the load balancer uses an instance ID and port combination to record the container. While routing traffic, this ID and port combination, which is linked to the container, is taken into consideration.

 Application load balancer

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#3) Classic load balancer: This is yet another type of load balancer which decides on routing based on either the transport layer or application layer. A strong flexible connection between the load balancer port and container instance port is a prerequisite.

Also, the mapping needs to make sure that the cluster has a minimum of those many container instances as the required count of each service, which is using a classic load balancer.

Classic load balancer

#4) Gateway load balancer: This load balancer works on a third layer of the Open Systems Interconnection (OSI) model. It allows the deployment, scaling, and management of virtual appliances like firewalls and deep packet inspection systems in the cloud.

It works by combining the network gateway, i.e. the single point of entry and exit for all traffic, and the process of distribution of traffic when virtual appliances are scaled to meet increased demand. It listens for all IP packets on all ports and the traffic is routed to the target group defined by the listener rules.

Gateway load balancer

#5) Server load balancer: This type is primarily a data center architecture that evenly distributes network traffic across servers. This even distribution of load prevents overloading of anyone particular server and makes sure the availability of applications along with maintaining the health of the application and server.

Server load balancer

#6) Global server load balancing: This type is mainly used in cases of data center failover and to improve the experience for end-users. It uses geolocation for routing users to their closest data centers. This load balancer is based on the DNS system. The availability and performance of the data center are considered for the manipulation of DNS response.

There are a few more types of load balancers which have been listed below:

  • Hardware load balancer: A hardware load balancer uses the physical, on-premises hardware for the distribution of traffic for applications and networks. These are appliances that can manage huge traffic volumes. These devices are also fairly expensive and have limited flexibility.
  • Software load balancer: Software load balancer primarily has two forms, namely commercial or open-source. These must be installed before use and are an affordable option as compared to a hardware solution.
  • Virtual load balancer: This type of load balancer is different from the software load balancer. The software of a hardware load balancing device is deployed on a virtual machine.

Frequently Asked Questions

Q #1) What happens when the load balancer fails?

Answer: In case of failure of one load balancer, it is the secondary load balancer that springs into action. The link between load balancers is strong and can effectively monitor status. When all load balancers fail, servers are offline till the time the problem is resolved.

Q #2) When would you use a load balancer?

Answer: Load balancers are typically used to enhance the capacity of applications and make them more reliable for users. The overall performance of the application increases when the load on servers that are associated with that application is reduced.

Q #3) What is the difference between load balancing and clustering?

Answer: Clustering refers to running a program on multiple machines (nodes) and the reason for doing this is load balancing. When one machine is overloaded, a cluster of machines can be used and a load balancer can be used to effectively distribute the load to different nodes in the cluster.

Q #4) What is HALB?

Answer: High Availability Load Balancing (HALB) plays an important role in avoiding failure of those components which are critical and their failure can be catastrophic for the organization. This system is based on the concept of using primary and secondary load balancers, which can manage the distribution of workload across data centers automatically.


For an IT company, it is extremely important to maintain and monitor the performance of its processes and applications. This makes load balancing a critical element that can ensure the availability and reliability of applications and prevents any impact on the end-user experience.

In this article, we have discussed what is load balancing. The article also explains the benefits and enumerates the types of load balancers.

We hope this article will benefit readers to gain an in-depth understanding of load balancers.