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What is AWS Elastic Load Balancing and How Does it Work?


Dhaval Rathod

3rd January 2024

How can businesses ensure high availability and scalability for their applications in today's cloud computing world?

One answer lies in Amazon Web Services' (AWS) powerful solution: Elastic Load Balancing (ELB). By intelligently distributing incoming traffic across multiple instances, ELB not only optimizes resource utilization but also enhances reliability and minimizes service disruption.

 But what exactly is ELB and how does it transform the cloud computing experience for businesses? Let's delve deeper into this cutting-edge technology and discover how it can revolutionize your application's performance.


Imagine you run an e-commerce website that experiences high traffic during peak seasons.

To ensure the site remains available and performs well, you implement Elastic Load Balancing (ELB) from Amazon Web Services (AWS). ELB automatically distributes incoming traffic across multiple instances, optimizing resource usage and enhancing reliability.

During normal periods, it evenly spreads traffic across instances. When traffic surges, ELB scales up by adding more instances to handle the load. If an instance fails, ELB redirects traffic to healthy instances, minimizing disruptions. ELB ensures your website stays responsive and reliable, even during peak demand.

Benefits of Using Elastic Load Balancing
High Availability

ELB eliminates single points of failure by distributing traffic across multiple instances. In case of an instance failure, ELB seamlessly redirects traffic to healthy instances, ensuring uninterrupted service.


ELB automatically scales resources up or down based on traffic fluctuations. This dynamic scaling ensures optimal performance and prevents overloading of instances during peak periods.

Fault Tolerance

By intelligently distributing traffic, ELB minimizes service disruption in the event of an instance failure. It redirects traffic to other healthy instances to maintain consistent application access.

Improved Performance

ELB balances traffic across instances that are geographically closer to users, reducing latency and improving the overall application experience.

How Elastic Load Balancing Works
Health Checks

ELB periodically sends requests to instances to assess their health and availability. Instances that fail health checks are automatically removed from the load balancer's rotation, ensuring only healthy instances handle incoming traffic.

Distribution Algorithms

ELB employs various distribution algorithms to evenly distribute incoming traffic across healthy instances:

1. Round-robin: Traffic is distributed sequentially to instances in a rotation.

2. Least outstanding requests: Traffic is routed to the instance with the fewest outstanding requests.

3. IP hash: Traffic is distributed based on the source IP address, ensuring requests from the same IP are consistently routed to the same instance.

Connection Management

ELB manages connections between clients and instances. By intelligently balancing the number of connections per instance, ELB prevents overloading and maximizes resource utilization.

SSL Termination

ELB can offload the encryption and decryption of SSL/TLS traffic. This not only reduces the computational burden on instances but also improves their overall performance.


ELB can be configured to distribute traffic across multiple availability zones, ensuring fault tolerance and high availability. This setup ensures that even if an entire availability zone becomes unavailable, the application remains accessible through other healthy instances.

Auto Scaling Integration

ELB seamlessly integrates with Amazon EC2 Auto Scaling. This integration enables dynamic scaling of instances based on incoming traffic load, ensuring optimal resource allocation and enhancing application responsiveness.

Types of Elastic Load Balancers

AWS Elastic Load Balancing offers three types of load balancers, each designed for different use cases:

1. Classic Load Balancer (CLB)

The Classic Load Balancer is the original ELB and provides basic load balancing capabilities. It operates at the transport layer (Layer 4) of the OSI model and supports TCP and SSL protocols. CLB can work with both EC2 instances and on-premises servers.

2. Application Load Balancer (ALB)

The Application Load Balancer operates at the application layer (Layer 7) of the OSI model and offers advanced features compared to the Classic Load Balancer. ALB supports HTTP and HTTPS protocols, enabling path-based and content-based routing. This makes ALB ideal for applications with complex routing requirements, such as microservices architectures.

3. Network Load Balancer (NLB)

The Network Load Balancer is designed to handle high volumes of traffic and provide ultra-low latency. Operating at the connection level (Layer 4) of the OSI model, NLB supports TCP, UDP, and TLS protocols. NLB is the best choice for applications that require extreme performance, such as gaming or streaming platforms.

Configuring Elastic Load Balancing

Configuring Elastic Load Balancing involves the following steps:

1. Creating a Load Balancer: Choose the type of load balancer, configure listeners and security settings, and select the availability zones.

2. Configuring Target Groups: Specify the instances or services that will be behind the load balancer. Target groups enable more granular routing and health checking.

3. Setting up Health Checks: Define the conditions and intervals for health checks on the instances. ELB continuously monitors the health of instances and automatically removes unhealthy instances from the rotation.

4. Configuring Routing Rules: Set up routing rules to determine how traffic is distributed to the target groups based on the incoming requests. Routing rules can include path-based routing, content-based routing, or host-based routing.

5. Monitoring and Scaling: Enable monitoring of your load balancer's metrics and set up auto-scaling policies to automatically adjust the number of instances based on traffic load. This ensures your application maintains optimal performance during peak traffic periods.


AWS Elastic Load Balancing improves the reliability and scalability of cloud applications by distributing traffic across multiple instances. Its advanced features ensure flexibility and adaptability to meet any application architecture needs. Configuring ELB is a straightforward process involving target groups, health checks, routing rules, and auto-scaling policies. For expert assistance in configuring AWS Elastic Load Balancing, contact CloudStakes today.