July 13, 2023

AWS Elastic Load Balancer – The Ultimate Guide

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By Andrei Maksimov

July 9, 2023

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Navigating the cloud can be complex, especially when balancing incoming application traffic. We’ve been there, too, struggling with heavy web traffic, so we dove into exploring Amazon’s Elastic Load Balancer (ELB) – a service that distributes load efficiently across multiple targets.

This ultimate guide will unravel everything you need about Amazon’s Elastic Load Balancer (ELB), from understanding its intricacies and benefits to using it at full throttle to increase your app’s scalability.

Key Takeaways

  • AWS Elastic Load Balancers (ELB) is an essential service for balancing incoming application traffic in the cloud, providing scalability and reliability.
  • ELBs offer benefits such as improved application scalability, fault tolerance, high availability, secure load balancing, efficient traffic distribution, handling of sudden traffic spikes, and hybrid load balancing abilities.
  • However, potential drawbacks of ELBs include latency issueslimited customization options, complexity in application architecture, cost considerations, and overloading problems. It is important to consider these factors when implementing ELBs into your infrastructure.
  • Several types of ELBs are available in AWS, including the Classic Load Balancer, Network Load Balancer (NLB), Application Load Balancer (ALB), and Gateway Load Balancer. Each type has its unique capabilities and use cases.

Understanding Elastic Load Balancers

Diving into the world of AWS Elastic Load Balancers (ELB), we find a service that brings scalability and reliability to our plates. As cloud engineers, it serves as our formidable ally in adjusting quickly to changes in application traffic, proving itself a key player in elasticity.

An ELB distributes incoming traffic across multiple targets, such as EC2 instances or containers running on ECS, ensuring load balancing is maintained and not just one resource is overloaded.

In addition to this essential task, the ELB monitors the health of these registered targets meticulously. Only healthy targets receive traffic, thus guaranteeing a high availability and fault tolerance for applications housed on Amazon AWS infrastructure.

Moreover, ELBs spread out application requests evenly across all availability zones within a region, further enhancing overall system resilience, which is crucial in an on-premise setup or a hybrid load-balancing situation.

However, no service comes without challenges; considerations like latency introduction by ELB and limited customization options must be considered while integrating them into your system architecture.

Advantages of Elastic Load Balancers

Elastic Load Balancers bring a myriad of benefits to the table when it comes to cloud engineering and application deployment. Here are some of the key advantages:

  1. Improved Application Scalability: Elastic Load Balancer (ELB) scales up automatically in response to incoming application traffic, ensuring optimal performance and capacity even during traffic spikes.
  2. Fault Tolerance and High Availability: ELB continually checks the health status of registered targets, directing traffic only towards healthy instances. This leads to high availability and resilience against single-point failures.
  3. Secure Load Balancing: By integrating with Amazon VPC, ELB offers secure load balancing features that protect your applications from threats.
  4. Efficient Distribution of Traffic: ELB distributes incoming traffic evenly across all availability zones within a region, improving fault tolerance.
  5. Handling Sudden Traffic Spikes: Thanks to its elastic scalability feature, ELB can conveniently handle sudden increases in traffic and millions of requests per second without breaking a sweat.
  6. Hybrid Load Balancing Abilities: ELB provides hybrid load balancing, balancing applications on both on-premises setups and AWS infrastructure making migration to the AWS cloud more accessible than ever.

Potential Drawbacks of Elastic Load Balancers

As proficient in managing and optimizing cloud systems, we understand that while AWS Elastic Load Balancers offer numerous benefits, they come with challenges. These drawbacks are important when deciding on the best infrastructure for our needs.

  1. Latency Issues: Elastic Load Balancer can introduce latency into applications as traffic must pass through the load balancer before being routed to targets. This added transition can potentially slow down response times.
  2. Limited Customization Options: ELB has limited customization options, often requiring additional tools and services to meet application requirements fully. This can add to the complexity of implementing your cloud solutions effectively.
  3. Complexity in Application Architecture: Using an ELB necessitates managing and maintaining additional resources, adding more complexity to the system architecture.
  4. Cost Considerations: ELB can increase overall AWS costs, especially if high traffic volume or multiple load balancers are needed. We need to consider these factors when calculating budgets for our projects.
  5. Overloading Problems: A significant drawback related to Elastic Load Balancers is their inability to process requests efficiently when overloaded or underloaded. Unpredictable traffic spikes may result in significant delays or even AWS outages.

Types of Elastic Load Balancers

Several Elastic Load Balancers are available in AWS, including the Classic Load Balancer, Network Load Balancer, Application Load Balancer, and Gateway Load Balancer.

Classic Load Balancer

Classic Load Balancer is a service provided by Amazon that distributes incoming application traffic across multiple targets like EC2 instances, containers, and IP addresses. It helps improve application scalability and performance by automatically scaling to handle changes in traffic demand.

Classic Load Balancer continuously monitors the health of registered targets and only routes traffic to healthy targets, ensuring high availability and fault tolerance. By evenly distributing traffic across all availability zones in a region, it enhances fault tolerance.

Operating at the OSI model’s transport layer (Layer 4), Classic Load Balancer performs load balancing using TCP and SSL protocols. With support for HTTP and HTTPS protocols, it can route traffic to applications based on different rules and conditions.

Network Load Balancer

The Network Load Balancer is an Elastic Load Balancer provided by AWS that allows cloud engineers to distribute incoming TCP traffic across multiple targets efficiently. With support for elastic or static IP addresses, the Network Load Balancer ensures highly scalable and reliable application delivery in the cloud environment.

It operates at the transport layer, providing advanced load-balancing capabilities for applications requiring low latency and high throughput. The Network Load Balancer enhances application performance and availability by intelligently routing client traffic to healthy targets across Availability Zones.

Its robust monitoring and auditing features enable cloud engineers to manage their network infrastructure effectively while ensuring secure and efficient traffic distribution.

Application Load Balancer

The Application Load Balancer (ALB) is a powerful load-balancing service provided by AWS. It operates at the application layer of the OSI model, allowing it to make routing decisions based on content.

This makes ALB perfect for applications that require advanced features like path-based and host-based routing. With ALB, you can handle HTTP, HTTPS, and WebSocket traffic efficiently, ensuring seamless performance for your applications.

One of the standout features of ALB is its ability to handle SSL offloading. By offloading SSL processing from backend servers, ALB improves performance and reduces its workload.

This ensures that your applications run smoothly even under heavy traffic loads.

In addition to its impressive routing capabilities, ALB offers other powerful load-balancing features. You can easily distribute traffic evenly across multiple target groups and dynamically scale resources based on demand.

Gateway Load Balancer

Gateway Load Balancer is a powerful feature offered by AWS Elastic Load Balancers that simplifies the management and scaling of third-party virtual appliances. It is specifically designed to handle these appliances’ installation, configuration, and routing of network traffic.

With Gateway Load Balancer, cloud engineers can easily scale their infrastructure while maintaining high availability and performance. This load balancer distributes incoming application traffic across multiple instances in different availability zones, ensuring efficient resource utilization and minimal downtime.

By leveraging the capabilities of Gateway Load Balancer, cloud engineers can streamline their workload management processes and focus on other critical aspects of their infrastructure.

How to Configure an Application Load Balancer in AWS

To configure an Application Load Balancer in AWS, follow these steps:

  1. Access the AWS Management Console or use the AWS Command Line Interface (CLI) to navigate to the EC2 dashboard.
  2. Click on “Load Balancers” in the navigation pane and then click on “Create Load Balancer”.
  3. Select “Application Load Balancer” as the type of load balancer you want to create.
  4. Choose a name for your load balancer and select the appropriate VPC where your application is running.
  5. Configure listeners by specifying the protocol and port(s) that your load balancer should listen on.
  6. Add target groups by defining how traffic should be distributed among registered targets (EC2 instances or IP addresses).
  7. Configure health checks to ensure that only healthy targets receive traffic.
  8. Set up security groups to control inbound and outbound traffic for your load balancer.
  9. Review and create your Application Load Balancer.

Cross-Zone Load Balancing: An Overview

Cross-Zone Load Balancing is a crucial feature AWS Elastic Load Balancers (ELB) offers that significantly ensures high availability and fault tolerance for cloud-based applications.

This feature distributes incoming traffic evenly across all Availability Zones where registered targets are available, optimizing resource utilization and reducing latency.

By enabling Cross-Zone Load Balancing, you eliminate the need for manual configuration and ensure that traffic is automatically routed to healthy instances in other zones if one zone fails.

This ensures seamless scaling and load balancing across multiple zones, simplifying resource management and minimizing the risk of downtime. Moreover, it is designed to handle sudden spikes in traffic and can support millions of requests per second.

For cloud engineers managing highly available applications, enabling Cross-Zone Load Balancing is strongly recommended. It ensures better performance, scalability, and availability for your applications and efficiently utilizes resources without any manual intervention.

So whether you have unevenly distributed instances or an imbalance in traffic distribution across zones, this powerful feature will help optimize your application’s performance while delivering a seamless user experience for your customers.

Elastic Load Balancing Pricing: What to Expect

There are a few key factors to consider regarding Elastic Load Balancer pricing. First, the pricing for load balancers varies depending on the type you choose: Classic Load Balancer, Application Load Balancer, or Network Load Balancer.

Each has its unique pricing structure.

For the Classic Load Balancer, you’ll be charged based on the number of active hours and the amount of data transferred. On the other hand, both Application and Network Load Balancers operate on a combination of load balancer hours and Load Balancer Capacity Units (LCU) used.

It’s worth noting that data transfer rates between load balancers within the same availability zone are free. However, additional charges will apply if you’re transferring data between availability zones within AWS.

To help users estimate their costs accurately, AWS offers a free tier that includes 750 hours of usage for Classic Load Balancers and 15 LCUs for both Application and Network Load Balancers.

Finally, remember that load balancer pricing is separate from other AWS services you may use in conjunction with them. So make sure to factor in any EC2 instance or data transfer costs when planning your budget.

AWS understands the importance of cost optimization to its customers’ success. That’s why they offer features like autoscaling and capacity reservation as part of Elastic Load Balancing to help users optimize their load-balancing costs effectively.

AWS Elastic Load Balancer Metrics: What to Monitor

Monitoring your Elastic Load Balancer metrics maximizes performance and ensures a smooth user experience. Here are important metrics you should be monitoring:

Request CountThis measures the number of requests processed by your load balancer. A sudden increase may indicate a traffic spike, while a decrease could suggest issues with your application or network.
HealthyHostCountThe number of healthy instances registered with your load balancer. A decrease here can signal a potential problem with your EC2 instances.
UnHealthyHostCountThe number of unhealthy instances registered with your load balancer. An increase here is a clear sign of trouble.
LatencyCounts the HTTP 5XX server error codes generated by the load balancer. An uptick in this number may indicate issues with the load balancer.
HTTPCode_ELB_5XXCounts the number of HTTP 5XX server error codes generated by the load balancer. An uptick in this number may indicate issues with the load balancer.
BackendConnectionErrorsThe number of failed health checks. Frequent failures can point to issues with your instances or network.

Monitoring these metrics will help us keep an eye on the performance of our load balancer, allowing us to respond quickly to potential issues. Regularly checking and understanding these metrics is key to maintaining our applications’ high availability and reliability.


How does Elastic Load Balancer distribute traffic across multiple targets?

Elastic Load Balancer (ELB) from Amazon Web Services (AWS) distributes incoming traffic across multiple targets, such as Amazon EC2 instances, containers, and IP addresses, to enhance the application’s availability. It utilizes three load balancers (Application, Network, and Classic) with different traffic distribution algorithms based on round-robin, least outstanding requests, and flow hash algorithms. This ensures the load is spread evenly, preventing any single resource from being overworked. ELB also performs health checks on targets and only directs traffic to healthy ones, reducing application downtime risk. Finally, it dynamically scales its capacity according to traffic patterns to handle varying load levels.

Can I use Elastic Load Balancers with both EC2 instances and containers?

You can use Elastic Load Balancers (ELB) with Amazon EC2 instances and containers. ELB is a fully managed service by Amazon Web Services (AWS) designed to distribute incoming network traffic across multiple targets, including EC2 instances, containers running on EC2 instances or in ECS tasks, and IP addresses. The choice of target type depends on your application requirements. With ELB, you can ensure high availability and automatic scaling for applications deployed on EC2 instances and containers while benefiting from the service’s health checks and traffic distribution features.

Is it possible to configure cross-zone load balancing with Elastic Load Balancers?

Configuring cross-zone load balancing with Elastic Load Balancers (ELB) in Amazon Web Services (AWS) is possible. Cross-zone load balancing allows you to distribute incoming traffic evenly across all registered instances in all enabled Availability Zones. This leads to a more evenly distributed workload, enhancing your application’s performance and availability. For Application Load Balancers, cross-zone load balancing is enabled by default. You can enable or disable cross-zone load balancing at will for Network and Classic Load Balancers. Cross-zone load balancing can help reduce the risk of overloading a single Availability Zone by spreading the load more uniformly.

Does Elastic Load Balancer support SSL termination and offloading?

Elastic Load Balancer (ELB) in Amazon Web Services (AWS) does support SSL termination and offloading. With SSL termination, the ELB handles the computationally intensive process of decrypting SSL/TLS-encrypted traffic, relieving the backend servers from this task. This process, known as SSL offloading, helps to increase the efficiency of your backend servers and reduces their CPU utilization, thereby enhancing the overall performance of your applications. You can easily manage and deploy SSL/TLS certificates via AWS Certificate Manager and associate them with your ELB. It’s also worth noting that Application Load Balancers and Classic Load Balancers support SSL termination and offloading.

What are some best practices for monitoring and optimizing the performance of Elastic Load Balancers?

There are several best practices for monitoring and optimizing the performance of Elastic Load Balancers (ELB). Use Amazon CloudWatch to track ELB metrics such as request count, latency, and backend connection errors for insight into your application’s performance and to set up alarms for anomaly detection. Enable access logs to analyze traffic patterns and identify potential security risks. To optimize performance, enable cross-zone load balancing to distribute traffic evenly across all registered instances and configure connection draining to maintain active sessions during instance de-registration. Use health checks to direct traffic away from unhealthy instances. Also, scale your backend resources appropriately to handle traffic spikes and utilize SSL offloading for better resource utilization.

Can I use Elastic Load Balancers with on-premise resources in a hybrid cloud environment?

In a hybrid cloud environment, you can use Elastic Load Balancers (ELB) with on-premise resources. ELB supports registering IP addresses as targets, including IP addresses from on-premises resources. You can achieve a hybrid cloud architecture by integrating on-premises resources and AWS resources via AWS Direct Connect or VPN connections. This allows ELB to distribute incoming application traffic across both AWS and on-premises resources, optimizing the load distribution and enhancing the availability of your application. However, it’s crucial to note that the on-premise resources must meet certain requirements and that any IP targets must be within the RFC 1918 or RFC 6598 private IPv4 address ranges.

What security features are available with Elastic Load Balancers to protect against cyber threats?

Elastic Load Balancers (ELB) in Amazon Web Services (AWS) offer a variety of security features to protect against cyber threats. ELBs support SSL/TLS termination, which provides secure communication between clients and load balancers. You can integrate ELBs with AWS WAF (Web Application Firewall), which allows you to monitor HTTP and HTTPS requests and block common web-based attacks. ELBs can be integrated with AWS Shield for protection of DDoS (Distributed Denial of Service). They support security groups to control inbound and outbound traffic and Access Control Lists (ACLs) for IP-level filtering. Additionally, AWS Certificate Manager allows easy SSL certificate management, and ELB Access Logs provide detailed records of all requests made to the ELB, aiding in security analysis.

How can I ensure high availability and fault tolerance with Elastic Load Balancers in AWS?

To ensure high availability and fault tolerance with Elastic Load Balancers (ELB) in Amazon Web Services (AWS), employ a multi-Availability Zone (AZ) architecture. Register instances in multiple AZs with your ELB to distribute incoming traffic. If one AZ fails or becomes overloaded, ELB automatically reroutes traffic to instances in the remaining healthy AZs. Use ELB’s health checks to send traffic only to healthy instances. For high availability, enable cross-zone load balancing to distribute traffic evenly across all registered instances in all enabled AZs. You can also use Auto Scaling Groups with ELB, ensuring the dynamic adjustment of your compute capacity in response to traffic patterns and maintaining high availability even during demand spikes.

Is there a way to automatically scale the capacity of Elastic Load Balancers based on traffic demand?

Elastic Load Balancers (ELB) in Amazon Web Services (AWS) automatically scale their capacity based on incoming application traffic. They are designed to handle traffic peaks and valleys without requiring manual intervention. The ELB adjusts its request processing capacity according to incoming traffic patterns and scales in response to the number of active connections or the rate of new connections, providing consistent performance. To help manage backend resources, combine ELB with AWS Auto Scaling groups. This way, you can automatically scale the number of EC2 instances based on demand, ensuring an efficient, balanced load across all available resources and high availability for your applications.


In conclusion, AWS Elastic Load Balancers are crucial for improving application scalability and performance in cloud environments. With its ability to automatically distribute traffic across multiple targets and ensure high availability, ELB plays a vital role in maintaining the reliability of applications.

However, it is important to consider the potential drawbacks and costs associated with ELB implementation. By understanding the different types of load balancers available and properly configuring them in an AWS infrastructure, cloud engineers can harness the full power of ELB to optimize their applications for seamless user experiences.


Here’s a list of the most important sources of information about AWS ELB:

  1. What Is Elastic Load Balancing?
  2. Elastic Load Balancing Documentation
  3. How Elastic Load Balancing Works
  4. AWS Elastic Load Balancer Types
  5. Configuring Your Classic Load Balancer
  6. Network Load Balancers
  7. Application Load Balancers
  8. Gateway Load Balancer
  9. Configuring Your Application Load Balancer
  10. Cross-Zone Load Balancing
  11. AWS Elastic Load Balancer Pricing
  12. CloudWatch Metrics for Your Classic Load Balancer
  13. CloudWatch Metrics for Your Application Load Balancer
  14. CloudWatch Metrics for Your Network Load Balancer

Remember, these references will help you navigate various aspects of working with AWS Elastic Load Balancers efficiently. Whether configuring load balancing in the management console or integrating ELBs into your existing infrastructure, these resources are invaluable tools in optimizing application performance and ensuring high availability.

Andrei Maksimov

I’m a passionate Cloud Infrastructure Architect with more than 20 years of experience in IT. In addition to the tech, I'm covering Personal Finance topics at https://amaksimov.com.

Any of my posts represent my personal experience and opinion about the topic.

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