What are Network Load Balancers and their Benefits?

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Today, everyone hops on to the internet to search for answers to their queries, play music and videos, share images, converse, and much more. With a large number of applications wanting to process data correctly and quickly, the load on the network is immense.

Therefore, it is vital to use tools that can help maintain the equilibrium of high-traffic demands, such as cloud applications, web services, and large-scale enterprises. One such tool that helps applications respond timely is a network load balancer.

Helping ensure seamless, efficient, and reliable network performance, these network load balancers help enhance the performance of applications with multiple resource servers and duplicated data. Read on to find out more about the importance of network load balancers. 


Network load balancers are simple devices that operate between the server and the user, helping ensure that all resource servers are used equally by distributing network traffic dynamically across a network of resources that support an application. These resources include WAN links, servers, and virtual machines. 

This helps improve the reliability and availability of the network resources in times of high usage and demand, ensuring a better uptime and user experience. A load balancer has the following components:

  1. Listener, which checks the connection request from clients with the protocol and port, forwarding it to a target group.
  2. A target group that routes the requests to one or more registered targets. These target groups support the TCP, UDP, and TLS protocols.
  3. Load balancer, which serves as the single point of contact for clients, distributing traffic across different targets.

A network load balancer functions on Layer 4 of the Open Systems Interconnection (OSI) model and can handle up to millions of requests each second. You can also enable multiple availability zones for a load balancer to help increase the fault tolerance of applications. This also helps ensure that each availability zone has a minimum of one registered target for each group.

It is vital to note that network load balancers consider only the network-layer information contained inside the packets they direct. They are not intended to be aware of the application layer that includes the content type, cookie data, user location, or application behavior.

Create a IPv4 Network Load Balancer

Step 1: Create a Target Group

First, create a target group to register your EC2 instances. Replace <vpc-id> with your actual VPC ID.

aws elbv2 create-target-group \
    --name my-target-group \
    --protocol TCP \
    --port 80 \
    --vpc-id <vpc-id> \
    --target-type instance

Step 2: Register Targets

aws elbv2 register-targets \
    --target-group-arn <target-group-arn> \
    --targets Id=<instance-id-1> Id=<instance-id-2>

Step 3: Create a Network Load Balancer

aws elbv2 create-load-balancer \
    --name my-network-load-balancer \
    --type network \
    --subnets <subnet-id-1> <subnet-id-2>

Step 4: Create a Listener

aws elbv2 create-listener \
    --load-balancer-arn <load-balancer-arn> \
    --protocol TCP \
    --port 80 \
    --default-actions Type=forward,TargetGroupArn=<target-group-arn>

Step 5: Verify the Load Balancer

aws elbv2 describe-load-balancers --load-balancer-arns <load-balancer-arn>

Step 6: Check the target health

aws elbv2 describe-target-health --target-group-arn <target-group-arn>

Operation of Network Load Balancer 

As mentioned above, a network load balancer functions at the fourth layer of the Open Systems Interconnection model. When the load balancer gets a connection request, it selects a target from a default target group.

Next, it tries to open a TCP connection, selecting the target on the port specified by the user. By enabling an availability zone for the load balancer, you allow the Elastic Load Balancing to create a load balancer node.

This node distributes traffic across the registered targets in its specified availability zone. You can also enable cross-zone load balancing. This helps increase the fault tolerance of your applications. 

When in TCP traffic, the load balancer selects the target using a flow hash algorithm formed on the source IP address, source port, protocol, destination IP address and port, and the TCP sequence number. 

On the other hand, for UDP traffic, the target is selected on the basis of the protocol, source IP address and port, and destination IP address and port, where the source and destination are the same. 

You can easily add or remove targets from your load balancer according to the requirements without disrupting the flow of requests. This is supported by Elastic load balances scales that can help scale the majority of workloads automatically. 

Common Network Load Balancer Algorithms

There are various load-balancing algorithms that you can use, including:

Round Robin

Using this algorithm, the load balancer distributes the traffic to a list of servers in rotation using the Domain Name System.


The threshold algorithm distributes the tasks based on a threshold value set by the user. 

Least Connection

Under this commonly used algorithm, a new request is sent to the server with the least number of current connections to clients. This algorithm analyses the relative computing capacity of each server to determine which has the least connections. 

Least Time

Under this algorithm, a request is sent to the server selected by combining the quickest response time and the fewest active connections.

URL Hash

With this algorithm, the load balancer generates a hash value based on the URL present, forwarding it to the servers and caching it. This allows the subsequent requests with the same URL to use the cache. 

Source IP Hash

With source IP hash, the client’s source and destination IP address are used to create a unique hash key, tying the client to a particular server.

Benefits of Network Load Balancers

With the growing reliability of network connections, users demand the real-time ability to browse the internet and get results. To ensure a quick response time and provide consistent results, a network load balancer is essential. Moreover, by helping smooth functioning during high spikes, a network load balancer also prevents problems in the internal server. 

Acting as a traffic proxy that distributes the network traffic across different endpoints, a network load balancer helps in:

  • Improving the reliability of applications by decreasing the burden on individual services or clouds and distributing the demand across different compute surfaces. 
  • Preventing lagging or downtime of applications.
  • Enabling scalability of applications by directing requests and traffic to other available compute surfaces.
  • Ensuring security solutions and their scalability. This can be done by distributing traffic across different backend systems, therefore minimising the attack surface. In addition, a load balancer can help redirect traffic to other systems if one of them is compromised. 
  • Enhances application performance by optimising uptime and ensuring reliability throughout demand spikes.
  • Preserves the client-side source IP, allowing the backend to see the client’s IP address for further processing by applications. 

Real-world Case Studies of Network Load Balancers

CompanyUse CaseBenefits Realized
NetflixStreaming Service Load BalancingImproved user experience with reduced buffering and latency
AirbnbWeb Traffic Management during Peak TimesEnhanced scalability and availability of the website
SpotifyMusic Streaming Load DistributionSmooth streaming with minimal interruptions
AmazonE-commerce Traffic Handling on Prime DayMaintained performance under high traffic volumes
UberReal-time Ride Matching and DispatchingFaster response times and efficient resource utilization

Advanced Configurations of Network Load Balancers

Configuration AspectTipBenefit
Health ChecksCustomize health check intervals and thresholds based on workloadEnsures optimal health and availability of targets
Target GroupsUse multiple target groups for different application componentsImproves load distribution and fault isolation
Listener RulesConfigure listener rules to route traffic based on host/path conditions to remove unhealthy targets gracefullyEnhances routing precision and application performance
Connection DrainingEnable connection draining to gracefully remove unhealthy targetsMaintains user sessions during target removal
Idle TimeoutAdjust idle timeout settings to match application session behaviorReduces unnecessary resource usage and costs

Pros and cons of Network Load Balancers

Feature/CriteriaNetwork Load Balancers (NLBs)Application Load Balancers (ALBs)Classic Load Balancers (CLBs)
LayerLayer 4 (Transport layer)Layer 7 (Application layer)Layer 4 and Layer 7
Use CaseHigh-performance TCP/UDP trafficHTTP/HTTPS traffic with advanced routingGeneral-purpose load balancing
ProsHigh performance, low latency, supports static IP, TLS terminationAdvanced request routing, SSL offloading, WebSocket supportSimplicity, support for both Layer 4 and 7, cost-effective for simple use cases
ConsLimited to basic load balancing, no content-based routingHigher complexity, may incur higher costsLess feature-rich compared to ALBs, may not support modern web applications
Ideal ForReal-time applications, gaming, IoTWeb applications, microservices, API-based servicesLegacy applications, small to medium-sized applications

Summing Up

Network load balancers are a vital tool used in the management of high-traffic networks. By ensuring uptime and reliable search results, network load balancers effectively distribute network traffic across multiple servers.

There are various types and alignments of network load balancers that you can choose from. Deploying an effective load balancer can help ensure easy scalability and high security and improve application performance.

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