Load Balancers Explained: How They Work and Why You Need One

A load balancer can be either hardware or software that is used in a device that distributes connections. They function somehow similarly to the ‘reverse-proxy’ as they represent app servers to the users via a virtual IP. Such technology is called an SLB or server load balancer. The SLB is used for the LAN networks as well as for pools of app servers within one website.

With the help of a load balancer, it is possible to understand the scalability and availability of the app. One app might require more resources than one server can provide. The load balancer works with the pool of servers by directing traffic through different algorithms. In case there is a necessity for more resources, then they can be added.

The load balancer checks the availability of the app on the server. In case of issues with some checking, the app is taken out of the pool of available servers. When problems with the specific app are fixed, then health care returns it to the pool.

Such balancers are between the app server and the users, so they can perform some additional functions. They can help with content switching and give security functions such as WAF and 2FA.  

Key Advantages of Load Balancing

The key advantages of this technology relate to the security, availability, and scalability of the app. Similarly, to the reverse proxy, load balancing is like a gate that controls and directs traffic volumes between the server and the users.

Common Applications of Load Balancing

• ​Automated recovery to the backup sites.
• ​Automatic detection of server issues and redirection of the traffic volumes.
• ​Removal and addition of the app servers.
• ​No impact during the server maintenance.
• ​Blocking of the suspicious content.

How a Load Balancer Functions

A load balancer functions by giving a virtual IP that represents the app to the user. This user connects to this address, and then the balancer, through the algorithms, determines whether a connection should be sent to a certain app on the server. Also, the balancer is responsible for the monitoring and management of the entire duration.

Let’s discuss the process of a function on a much simpler example—for instance, a real estate agent is helping a client with a property rent. The agent discusses some details with a client and sends a request to the property owner regarding the contract. The owner reacts with a specific proposition relating to the prices, and this information is given to the client through the agent. This process continues till signing a contract.

The major function of the agent, as well as a load balancer, is to balance the situation. In terms of the load balancer, it can deny/allow some details and impact the security level. It might also use authentication to check the reality of the user. Depending on the availability of the server, it can redirect to another server.  

Different Types of Load Balancers

Here we will discuss several types of load balancers so you will have a better understanding of technology as well as its history.

Network-Based Server Load Balancers

This technology appeared in the middle of the 1990s as a necessity, because of a sudden spike in traffic activity. The basic usage of balancers is related to the creation of a pool of servers to meet the available resources demand. The connection was made based on the packet header. Particularly, we are talking about a 5-tuple – IP protocol, destination port, source port, destination IP, and source IP. This was the beginning of network-based server load balancers or they were also known as Layer 4 balancers.

Application-Level Load Balancers

The technology never stands on the same point of evolving, it is a constant process with lots of modernizations and strategies. That relates to the load balancers as well, soon they got more features and started offering content switching and content awareness. Such balancers were more oriented toward the content payload rather than the packet header. Such balancers were called application-level or Layer 7 and looked at the URL, HTTP header.

Global Load Balancing Solutions

GSLB is a totally different approach compared with the initial load balancers. Global load balancing solutions function in real-time and are based on DNS, so they function by giving reactions based on specific algorithms. Such solutions can be compared with the dynamic DNS technology that functions by monitoring and managing various sites. Lots of great balancers that are available today offer GSLB as a helpful component.

Hardware-Based Load Balancing

Load balancers can also be related to the hardware solutions. Such an approach guarantees better performance characteristics and is usually used in data centers. Moreover, these options don’t need dependencies such as COTS hardware and hypervisors.

Software & Virtual Load Balancers

Nowadays, technologies have become more cloud-based because of the better flexibility. Moreover, such solutions load balancers can integrate with virtualization orchestration. When speaking about the software-based environments, they are based on CI/CD and DevOps processes.

Scalable Elastic Load Balancers

ELB has many more options and guarantees better scalability based on the traffic needs at any time. With the usage of such a solution, it is possible to scale traffic on the app. Also, there is an option for on-demand and automagical scalability. These balancers have way more fault tolerance of the app, because of the usage of request routing algorithms.

Understanding Load Balancing Algorithms

The algorithms are specific rules that are necessary for the connection to determine which server to send the connection to. There are various types of algorithms, and some of them might be really advanced ones where whereas some are very simple. The purpose of all the algorithms is to send the connection to the most suited app server.

The most used algorithm is one of the fewest connections. Such an algorithm functions by sending the connection to the best-performing server based on the number of connections. The least connections consider the length of each connection by evaluating currently active ones.  

Various Types of Load Balancing Algorithms

• ​Source IP hash
• ​Least connection
• ​Weighted round robin
• ​Weighted response time
• ​Round Robin
• ​Weighted least connection
• ​Chained failover