What Is a Load Balancer? Definition, Working, Benefits, and Drawbacks

• A load balancer is defined as a hardware or software tool that acts as a reverse proxy to distribute incoming traffic across the available servers in a server farm so that traffic is routed optimally and applications can perform correctly.
• As enterprise application landscapes become more complex, load balancers have become essential to improve UX, ensure app performance, and prevent outages.
• This article explains the meaning and working of load balancers and lists their key benefits and disadvantages.

What Is a Load Balancer?

A load balancer is a hardware or software tool that acts as a reverse proxy to distribute incoming traffic across the available servers in a server farm (following static or dynamic algorithms) so that traffic is routed optimally and applications can perform correctly.

Load Balancer Hardware Device

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Load balancing is the distribution of inbound network traffic among several backend servers, commonly called a server farm or pool. Modern high-traffic sites have to handle several thousand, if not tens of millions, of concurrent requests from users or clients and quickly provide the right content, pictures, videos, or application data. To scale to such enormous numbers cost-effectively, current best practices in computation usually necessitate adding more servers.

A load balancer functions as a wall at the forefront of the servers, distributing client demands across all servers that can fulfill them. It does this in a way that maximizes speed and capacity utilization while guaranteeing no server is overwhelmed, something that can negatively impact performance.

If a single server becomes unavailable, the load balancer reroutes traffic flow to the online residual servers. When an additional server gets included in the group, the load balancer sends requests to it automatically. This makes load balancers critical to any network, data center, mainframe, or server infrastructure.

Types of load balancers

While the main purpose of a load balancer may seem simple, its underlying operations are extremely sophisticated, allowing it to power high-volume and complex networks. Various types of load balancers have emerged to fulfill different network technology needs, such as:

1. Hardware load balancers

A hardware-led load balancer is a hardware tool that can safely process and reroute gigabytes of traffic among hundreds of different servers. You can house it in your data center and construct numerous virtual load balancers employing virtualization, or you can even operate it manually.

2. Software load balancers

Software-based load balancers are apps that conduct all the functions of load balancing. They are available for installation on any server or through a managed third-party service. Some network systems may have software-based load-balancing functions built in.

3. Global load balancers

These load balancers can function across various geographically dispersed servers. Companies can, for instance, possess servers in multiple data centers in different countries and on the cloud managed by third parties. Local load balancers handle the application burden within a specific area or zone in this situation. They shift traffic to a local server to reduce latency. However, in the event of server failure, they may need to reroute traffic to sites or servers in a different region, and this is where global load balancers come into play.

4. Application balancers

Multiple server farms with an assortment of servers devoted to a particular application are present in modern applications. To divert traffic, application load balancers analyze the request’s content. Consider an ecommerce application; the application load balancer forwards queries to view products to servers, which include images and videos but do not require active connections. It sends requests from purchasing carts to servers that can sustain multiple connections and store cart details for a longer duration.

5. Network balancers

Network load balancers analyze internet protocol (IP) addresses along with additional network data to optimally move traffic. They can track the origin of application traffic and allocate static IP numbers to multiple servers. Network load balancers manage server demand via static and dynamic load balancing algorithms, which have been outlined in a section later in this article.

What are load-balancing algorithms?

An algorithm is a collection of fixed, sequential rules determining a computer program’s functioning. A load balancer utilizes a load-balancing algorithm to split network traffic across multiple servers.

Static algorithms distribute traffic equally between servers but are infrequently used due to their sub-optimal performance. Instead, dynamic algorithms are applied, which distribute traffic in a contextualized manner, as per the following methods.

• Round robin algorithms: Incoming inquiries are successively distributed across an array of servers. If there are three application servers, for example, the initial request from the client goes to the first server in the sequence, the subsequent one to the next server, and the third to the last server. The fourth request will be delivered to the first server, followed by subsequent requests.
• Weighted round robin: It provides the ability to distribute inbound client requests throughout the server clustering, dependent on each server’s proportional capacity, in addition to being in a simple rotation.
• Least connections: A new request is transmitted to the system with the least active client connections. Each server’s relative processing capacity is considered when determining which has the fewest connections.
• Hash: Here, the load balancing algorithm spreads requests according to a parameter you establish, such as the IP address of the client’s computer or the request URL.
• Adaptive: Decisions are made by resource-based or dynamic algorithms according to indicators of status pulled from backend servers. Each server has a custom program or an ‘agent’ installed on it, which determines and sends a status indicator to the balancer.
• Random with two choices: This algorithm selects two servers randomly and then applies the least connections algorithm to dispatch a request to the selected server.
• Fixed weighted: Fixed weighting is a load-balancing algorithm wherein the administrator allocates weightage to every application server based on the proportionate traffic-handling capacity of every server in a server farm.

See More: What Is a Network Switch? Meaning, Working, Types, and Uses

How Does a Load Balancer Work?

The function of a load balancer is to operate as a reverse proxy. It assigns a virtual internet protocol address (VIP) to the client corresponding to the application. The client joins the VIP, and after that, the load balancer uses its algorithms to determine if the link should be routed to a specific application instance on a server. The connection is managed and monitored for its duration by the load balancer.

In fact, the function of a load balancer can be compared to the job of a traffic cop, as it is intended to methodically route requests to the right locations at any given moment and prevent wasteful bottlenecks and unexpected problems. Ultimately, load balancers must offer the efficiency and safety necessary to sustain a complex IT infrastructure and its many processes.

The role of a load balancer explained

Think of a Hollywood agent negotiating a new contract for a famous actor. The agent considers the actor’s request and sends it to an especially interested party, individual, or entity. The production company transmits the details (contract) back to the agent, who then forwards it to the client. This goes on for a while until something that works becomes apparent.

Now, apply the above theory to the load balancing domain. Server load balancing (SLB) is the principal function of the load balancer. Depending on the participant’s engagement with the dialogue, the agent can offer additional functionality. They can grant or deny access to specific details (security). They might want to confirm that the individual they are speaking with is indeed the actor and not a fraudster (authentication).

According to availability or region (geo-specific LB), the agent could pass on the discussion to a different production company if a deal with the present one doesn’t seem likely.

Steps in the working of a load balancer

The basic steps of a load balancer’s functionality are as follows:

• A load balancer is a tool or app that handles load balancing. It can be implemented as either hardware or software.
• The setting up of a specialized load-balancing device is required for hardware load balancers. Therefore, you should purchase, install, and configure the device.
• Load balancers based on software can function on a server, a machine that is virtual, or on the cloud. Frequently, content delivery networks (CDN) include load-balancing capacities. In this instance, the load balancer will be remotely installed and configured by the software provider. Additionally, you can elect to share the management of the software component.
• The load balancer allocates every incoming request from an individual user to a specific server, and the whole process is repeated for each request.
• Using a variety of algorithms, load balancers identify which server is responsible for every request. Two primary categories for these algorithms are dynamic and static. 
  • Algorithms for static load balancing distribute workloads without considering the immediate state of the system. A static load balancer is unaware whether the servers are operating inefficiently or underutilized. Instead, tasks are assigned according to a predetermined blueprint. Static load balancing is simple to implement but can lead to inefficiencies.
  • Dynamic load balancing algorithms consider each server’s accessibility, task load, and condition. They can transfer traffic from overloaded or inadequately performing servers to underutilized servers, thereby maintaining a stable distribution. However, configuring dynamic load balancing is slightly more complicated.
    Various factors affect server availability, including every server’s condition and general capacity, the magnitude of the distributed tasks, etc. The previously discussed algorithms are used in this step to facilitate the load balancer’s working.

• The server receives the request from the network — passed through the load balancer — and processes it. Since the most optimal server is selected, the app or process functions smoothly.

Web applications employ load balancing frequently. Load balancers that are software-based or housed in the cloud assist in distributing internet traffic equitably between the servers hosting the app.

Load balancers also find widespread application within large localized networks such as data centers and office networks. In the past, this required hardware machinery such as application delivery controllers (ADCs) or a specialized load-balancing device. However, organizations are gradually moving toward greater virtualization, for example, through network function virtualization (NFV).

Modern technologies such as NFV and software-defined networking (SDN) make it possible to optimize load balancing without using a physical device. Load balancing is a highly scalable method meant to handle the many queries resulting from modern multi-app, multi-device processes, regardless of whether you use hardware or software. It facilitates a more reliable and consistent end-user experience for employees.

See More: What is DHCP (Dynamic Host Configuration Protocol)? Meaning, Working, and Features

Pros and Cons of Load Balancers

When implementing load balancers in your computer network, understanding their pros and cons is crucial. Here, we’ve listed the various advantages and disadvantages of load balancers.

Load Balancer Pros and Cons

Pros of load balancers

Using a load balancing device or software, you can:

1. Improve uptime

Server failure or upkeep downtime can result in a more severe application outage, rendering an app unavailable. By automatically detecting server issues and diverting client traffic to readily accessible servers, load balancers improve the fault resilience of systems.

By rerouting traffic to an alternative server, server repairs or upgrades can be carried out with zero disruptions. This is also beneficial for disaster recovery, where traffic can be proactively directed to backup sites.

2. Scale applications with confidence

Load balancers can intelligently distribute network traffic across multiple servers. Load balancing eliminates congestion on individual servers, enabling applications to handle hundreds of thousands of client requests seamlessly. They can even forecast traffic via dynamic algorithms, letting you add or delete servers as required.

3. Boost network and application performance

Load balancers enhance application efficiency by lowering network latency and bolstering response time. They distribute workload proportionately across servers so each server can function at maximum capacity. You can also configure load balancers to reroute client requests to a geographically closer server, dramatically lowering app latency.

4. Protect applications from network-related attacks

Today’s load balancers include built-in network security protocols, offering an additional layer of protection for web applications. They are a useful tool in the fight against distributed denial of service (DDoS) attacks, wherein assailants overwhelm the app or system with countless simultaneous requests, resulting in server failure. Even if you cannot avoid such an attack, you can autonomously reroute attacker traffic to various backend servers to mitigate its effects.

Balancers with the proper configuration will direct traffic via an array of interconnected firewalls for added security. Load balancers can additionally monitor traffic and instantly block malicious content.

5. Deliver better user experience (UX)

Load balancers can improve UX if a company operates high-traffic websites, applications, or datasets that generate a lot of queries. It optimizes the consumption of resources, the transmission of data, and response time to offer end users the best possible service. In high-traffic settings, load balancing ensures the seamless and precise execution of user requests. It ensures users do not have to contend with sluggish or unresponsive apps or resources.

6. Make IT operations more flexible

Employing several load-balanced servers gives IT administrators greater flexibility in managing website traffic. For example, they can execute server maintenance without influencing the site’s availability. With a scheduled maintenance system, at least one server will always be accessible to pick up the load while others undergo maintenance downtime. In a DevOps culture, where application changes are frequent and routine, load balancers make life easier for the operations team.

7. Share SSL decryption workloads with the server

If your website is SSL-certified, the servers take on an additional responsibility. Requests, as well as any associated data, are protected by encryption when delivered to an SSL website. The servers acquire this encrypted information and are tasked with decrypting it before beginning to process it. This consumes precious time as well as computational power.

Load balancers are crucial in such a situation. They decode the data before transmitting it to the web server. This allows the server to focus entirely on evaluating the input and relaying pertinent data. This conserves host computation resources that can be better utilized elsewhere.

See More: What Is MPLS (Multi-Protocol Label Switching)? Definition, Working, and Architecture

Cons of load balancers

The benefits of load balancers are overwhelming. Without load-balancing functionality in your network, you will likely witness inefficient resource usage and poor app performance. That said, it is also important to note the challenges you may face when using load balancers.

1. Geographic limitations in certain load-balancing algorithms

Some algorithms for load balancing are intended for very small areas. Communication interruptions, network pauses, space between distributed entities, and separation between the user and resources requested are not considered. Nodes in remote locations pose a challenge since the protocols aren’t intended to work in such environments.

2. Possibility of assigning only a single point of failure

Certain load-balancing protocols cannot support dispersed nodes and instead rely on a centralized node to make all decisions. In the unlikely scenario that the central node fails, every part of the computing environment would get compromised. To overcome this challenge, multiple nodes in the load balancing setup should be configured to handle traffic and make routing decisions.

3. Difficulty in keeping up with technological advancements

The on-demand availability of cloud services, the Internet of Things (IoT), high-bandwidth mobile applications, and blockchain have all transformed users’ expectations of online apps. A reliable load balancer must be able to accommodate changing consumer requirements, processing power, storage capacity, and system functionalities. However, it can be challenging to update load-balancing algorithms constantly.

4. Delays due to overly complex algorithms

Algorithms for load balancing are often a double-header with their own share of pros and cons. The complexity of specific algorithms can impact the overall efficacy of a system. It may result in minor but significant changes to migration time, defect tolerances, and speed of response. Regardless of the server burden, load-balancing algorithms should be adjusted to deliver the most optimum system performance.

See More: What Is Wifi 6? Meaning, Speed, Features, and Benefits

Takeaway

Load balancers are an enterprise networking staple, and with good reason. They ensure the efficient use of networking resources, improve user experience, and reduce downtime. Without load-balancing software or hardware, application performance will struggle, and even the security architecture could suffer. Integrating load balancers into your networking technology stack can improve system resilience and prepare for future eventualities.

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