What is an Application Load Balancer?

In the context of cloud computing and utilizing microservices for building complex applications and services, it is important to ensure high availability as well as efficient distribution of network traffic. This is where load balancers come into play. When it comes to different load balancer types, there is the Application Load Balancer (ALB) that can route traffic depending on certain conditions. This article explains what Application Load Balancers are, what they offer, how they function, their advantages, possible applications, and the comparisons with other load balancer types.

What is a Load Balancer?

A load balancer is a hardware device or software program that aims to divide the network or application traffic among many servers. The main objective is to prevent a single server from getting overloaded with high traffic since this can cause the server to slow down or even crash. Using load balancers can improve the availability and reliability of applications due to the proper distribution of incoming traffic.

What are Application Load Balancers?

ALBs are a subset of load balancers that function at the application layer of the Open Systems Interconnection (OSI) model. Unlike conventional Load Balancers that operate at the network layer (Layer 4), ALBs can route based on the HTTP/HTTPS request content such as path, header, or cookie. This allows for more complex routing and better load balancing which makes ALBs ideal for modern web apps, microservices, and container systems.

Key Features of Application Load Balancer

Below are the key features of application Load Balancer

• Content-Based Routing: ALBs can forward traffic based on values within the HTTP request including host headers, path patterns, HTTP methods, and query strings. This makes it possible to come up with specific routing rules that will address the requirements of the application.
• SSL Termination: ALBs can perform SSL decryption, thus freeing backend servers from performing this computation intensive chore. This makes certificate management easy and at the same time enhances the overall performance of the backend solutions.
• WebSocket Support: ALBs natively support WebSocket to manage real-time, two-way connections between clients and servers required for applications such as live chats and notifications.
• Microservices and Container Support: ALBs also integrate effectively with the microservices and container based systems. They can forward the traffic to the different services depending on the content of the request, also it can help in load balancing and isolating different services as well.
• Health Checks: ALBs do health check on the registered targets (for example an EC2 instance or an IP address) to confirm that the targets are healthy and ready to receive traffic. Self-austerity takes place for unhealthy targets and they get excluded from the pool until they regain their health.
• Enhanced Security: There is a number of securities features available with ALBs, such as WAF integration, DDoS protection and IP list filtering.
• Automatic Scaling: ALBs can scale up or down according to the traffic, so it is effective in handling high-traffic applications as well as not consuming a lot of server resources during low-traffic applications.

How an Application Load Balancer Functions?

Application Load Balancers function by directing incoming application traffic across the appropriate targets, EC2 instances, microservices, or containers. Here's a simplified workflow:

• Client Request: A client initiates a call to a server hosting the application.
• DNS Resolution: And then, to the ALB, the DNS resolves the request.
• Listener Configuration: The ALB passively waits for incoming connections on specific ports such as port 80 for HTTP or port 443 for SSL.
• Rule Evaluation: The ALB proceeds to evaluate listener rules to discover how to handle the request. You can include everything from host headers, path patterns, HTTP methods, and so on.
• Target Group Selection: Following the rules set down, the ALB relays the request to one or more target groups, typically made of registered targets such as EC2 instances or IP addresses.
• Health Checks: The ALB always keeps watchful eye over health of targets within each target group. Operators who develop unhealthy targets are pulled out of circulation until they become sane.
• Response to Client: The selected target analyses the request and returns an appropriate response to the client through the ALB.

Advantages of the Application Load Balancers

Below are the advantages of application load balancer:

• Improved Performance: The use of ALBs also ensures that there is smooth distribution of traffic to the servers; hence, no server becomes overloaded by traffic, making the overall performance better.
• Enhanced Security: It would be valuable to note here that ALBs have inherent security features and work in combination with WAF to mitigate certain web exploits and other vulnerabilities.
• Increased Availability: ALBs help to improve application availability greatly through load balancing, which ‘shifts’ the traffic to working instances when others are down.
• Simplified Management: Here are the features that make ALBs beneficial and simplify the management of traffic:termination of SSL, as well as automatic scaling.
• Flexibility: ALBs provide content-based routing to microservices or containerized applications to help organizations manage and scale their services easier.

Use Cases of Application Load Balancer

Below are the use cases and applications of application load balancer:

• Microservices Architectures: In the context of request routing, ALBs work perfectly by directing the requests to the appropriate microservices based on the URL path or other HTTP attributes.
• Containerized Applications: The advanced load balancers can distribute traffic to containerized applications in platforms like Kubernetes and therefore provide high availability.
• HTTPS Termination: If backend servers perform SSL termination, ALBs may help to augment load and ease certificate management.
• Content-Based Routing: As ALBs are perfect targets for routing traffic based on content, typical use cases of multi-tenant applications may involve content routing or A/B testing environment.
• Real-Time Applications: It is important to note that WebSocket services are now supAported by ALBs and thus makes this load balancers appropriate to be used in real-time applications where long-lived bidirectional connections are needed.

Comparison with Other Types of Load Balancers

• Network Load Balancers (NLBs): Located at the transport layer (Layer 4) and are optimized for large volume, low delay routing. They are most useful for microservices apps that require a high-speed load balancer but do not offer content-based routing of Application Load Balancers.
• Classic Load Balancers (CLBs): Previous to ALBs, there are CLBs that work on the application and the network layers but with less advanced functionalities and more rigid than ALBs in terms of options. Over time, a sustainability transition is moving away from the traditional CLBs towards more progressive ALBs and NLBs.

Implementation Example

To illustrate the implementation of an Application Load Balancer, here’s a step-by-step guide for deploying an ALB on Amazon Web Services (AWS):

• Step 1. Create an ALB:
  • Log in to the AWS Management Console.
  • Navigate to the EC2 Dashboard and select "Load Balancers" from the left-hand menu.
  • Click "Create Load Balancer" and choose "Application Load Balancer".
  • Configure the basic settings, including the name, scheme (internet-facing or internal), and IP address type (IPv4 or dualstack).
  • Set up the listener by specifying the protocol (HTTP/HTTPS) and port.
• Step 2. Configure Security Settings:
  • Choose an existing security group or create a new one to control inbound traffic to the ALB. Ensure the security group allows traffic on the listener ports (e.g., 80, 443).
• Step 3. Set Up Routing:
  • Create target groups and register your instances, microservices, or containers with these target groups. Specify the target type (e.g., instance, IP, or Lambda function).
  • Define listener rules to specify how requests should be routed to the target groups. Rules can include conditions based on host headers, path patterns, HTTP methods, and query strings.
• Step 4. Configure Health Checks:
  • Set up health check parameters to monitor the health of targets. Parameters include the protocol, path, port, and threshold values for determining healthy targets.
• Step 5. Review and Create:
  • Review all the settings and click "Create" to create the ALB.
• Step 6. DNS Configuration:
  • Update your DNS records to point to the ALB’s DNS name, ensuring that client requests are routed through the ALB.

Conclusion

The load balancers are one of the most useful tools for managing application traffic as they provide an essential set of features and strict path for application traffic with many options focused on modern web applications and microservices architecture. As traffic distributors with the added intelligent content filtering and focus on performance, security, and availability, they work at enhancing the resilient IT infrastructures. It is therefore important that organizations seeking to apply or augment ALBs have a clear grasp of the concept, its components as well as the best practice for its deployment.

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Article Tags :

• System Design
• Load Balancer