The load balancer is a key device that ensures the smooth operation of many digital services. Its mission is to distribute incoming requests between several servers in order to avoid overload and ensure a rapid and efficient response. In other words, it acts like an orchestra conductor directing the flow of traffic through the servers to optimise the use of resources, maximise performance and minimise response times.
In this article, we take a closer look at this essential technology.
The different types of load balancer
A load balancer can be hardware or software and operate at different levels of the network protocol stack. Each type has its advantages, disadvantages and optimal use cases. Let’s look at these in detail.
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Hardware | These are physical devices designed to handle large-scale load balancing. They are typically deployed in a data center and can handle a high volume of traffic. They often come with advanced features and offer high performance, but can be expensive and less flexible than their software counterparts. |
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Software | These load balancers are applications installed on a server. Generally less expensive and more flexible than their hardware counterparts, they can be easily updated or modified. However, their performance may depend on the resources of the server on which they are installed. |
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Layer 4 | A network-based (or Layer 4) load balancer operates on the transport layer of the OSI model. It distributes traffic based on source and destination IP addresses, as well as port. While simpler and faster, it offers fewer options for managing traffic granularly. |
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Layer 7 | An application-based (or Layer 7) load balancer operates on the application layer of the OSI model. It makes more complex routing decisions based on the content of messages, such as URL, cookies, or HTTP headers. This allows it to offer more sophisticated load balancing, but it is generally slower than its network-based counterpart. |
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Key Providers | There are many load balancing solution providers, especially in the cloud domain. Among them are:
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How do load balancers work?
The algorithms used
A load balancer uses different algorithms to determine how incoming traffic should be distributed between servers. Here are some of the most commonly used algorithms:
- Round Robin: This is the simplest. It distributes requests cyclically to each server in the list, one at a time.
- Least Connections: This algorithm directs new requests to the server with the fewest active connections. This is useful when not all servers have the same capacity.
- IP Hash: This uses the origin and destination IP addresses to determine which server to send the request to. This is useful for ensuring session persistence.
Session management and persistence
For some applications, it is important that all user requests are directed to the same server for the duration of the session. This is known as “session persistence” or “session affinity”.
Let’s take a concrete example. Imagine that you add items to your shopping basket on a merchant site. This information may be stored on a specific server. Now, if your requests are redirected to another server, your basket could appear empty. To avoid this, load balancers use techniques such as cookies or the IP Hash algorithm to ensure that all your requests go to the same place.
Load Balancers - Checking the health of servers
It is imperative that a load balancer monitors the health of the servers it manages. So, if a server is determined to be down or unresponsive, the load balancer stops sending traffic to it until it is up and running again. This ensures that traffic is sent to servers that can handle it, improving the reliability and overall performance of the application.
Scalability and high availability
Another important aspect is their ability to manage scalability and high availability. By continuously monitoring server traffic and performance, a load balancer can help identify when new resources are needed, and ensure continuous service availability by rerouting traffic in the event of a server failure.
Conclusion
We have seen in this article that load balancers play an essential role in network traffic management. It is therefore clear that they are a crucial component of modern network infrastructure.
Load balancers contribute to operational efficiency by intelligently distributing traffic between servers, ensuring session persistence for a better user experience, and monitoring server health for optimum performance and availability.
As our dependence on online applications and services continues to grow, their importance will only increase. It is therefore essential for businesses and IT professionals to understand how they work and how to manage them effectively.
