What is AWS Load Balancer

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A Load Balancer in the context of cloud computing is a device or service that distributes incoming network traffic across multiple servers or resources. The goal is to ensure that no single server bears too much load, thus enhancing performance, reliability, and availability of applications. Amazon Web Services (AWS) offers a range of load balancing solutions through the Elastic Load Balancing (ELB) service.

AWS Load Balancer is designed to automatically distribute incoming application traffic across multiple targets, such as EC2 instances, containers, and IP addresses, in one or more availability zones. By spreading the load, AWS Load Balancers provide high availability, fault tolerance, and scalability to your applications.

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Types of AWS Load Balancer

AWS offers three main types of load balancers, each suited to different use cases:

1. Classic Load Balancer (CLB)
2. Application Load Balancer (ALB)
3. Network Load Balancer (NLB)
4. Gateway Load Balancer (GLB)

1. Classic Load Balancer (CLB)

The Classic Load Balancer is the original load balancer offered by AWS and operates at both the Layer 4 (Transport Layer) and Layer 7 (Application Layer) of the OSI model. CLB is ideal for simple, legacy applications that do not require advanced routing or high availability.

• Pros:
  • Simple to set up.
  • Suitable for basic applications and legacy systems.
• Cons:
  • Limited features compared to ALB and NLB.
  • Doesn’t support advanced routing like content-based routing or WebSockets.

2. Application Load Balancer (ALB)

The Application Load Balancer operates at Layer 7 (Application Layer) and is best suited for web applications that require HTTP and HTTPS traffic routing. ALB supports advanced routing capabilities such as path-based routing, host-based routing, and WebSocket support, making it ideal for microservices, container-based architectures, and modern web applications.

• Pros:
  • Advanced routing capabilities.
  • Supports HTTP/HTTPS and WebSockets.
  • Best for containerized applications (with ECS and Kubernetes).
• Cons:
  • Not ideal for non-HTTP(S) traffic.

3. Network Load Balancer (NLB)

The Network Load Balancer operates at Layer 4 (Transport Layer) and is designed to handle high-performance applications that require low-latency and high throughput. NLB is optimized to handle millions of requests per second while maintaining ultra-low latency.

• Pros:
  • Suitable for high-traffic, low-latency applications.
  • Supports TCP, TLS, and UDP traffic.
  • Provides static IP addresses.
• Cons:
  • Doesn’t support HTTP-based routing.
  • Limited advanced features like ALB.

4. Gateway Load Balancer (GLB)

The Gateway Load Balancer operates at Layer 3 and is designed to handle traffic destined for network virtual appliances (NVAs). It's primarily used for situations where you want to manage traffic to and from services like firewalls or intrusion detection systems.

• Pros:
  • Simplifies deployment of NVAs.
  • Supports both incoming and outgoing traffic for virtual appliances.
• Cons:
  • Less common for general-purpose applications.

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Load Balancer Algorithms in AWS

AWS Load Balancers use various algorithms to distribute traffic. The algorithm choice depends on the type of load balancer and your requirements. Here are the common algorithms used:

1. Round Robin (Default)

• How it Works: The Round Robin algorithm distributes incoming requests evenly to each target in the target group, regardless of their current load or performance. Once the last target is reached, the algorithm loops back to the first target.
• Use Case: Best used when all instances in your target group have the same processing power and the load is relatively balanced.

2. Least Outstanding Requests

• How it Works: This algorithm directs traffic to the target that has the least number of outstanding requests. It works well for web servers or services where some requests may take longer to process than others.
• Use Case: Ideal for applications with variable load or services where some requests are expected to be more resource-intensive.

3. Weighted Round Robin

• How it Works: This is an extension of Round Robin. You can assign weights to each target. A target with a higher weight will receive more traffic. For example, if a server has more CPU power or resources, it will handle more requests.
• Use Case: Useful when some targets are more powerful than others and can handle more traffic.

4. IP Hash

• How it Works: The IP Hash algorithm selects a target based on a hash of the IP address of the client making the request. This allows for session persistence, ensuring that a client is always routed to the same target.
• Use Case: Ideal for applications where sessions need to persist with the same server, such as in user logins or shopping carts.

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When to Use AWS Load Balancer?

AWS Load Balancer is ideal for:

1. High Availability: Distribute traffic across multiple instances or availability zones to ensure that your application remains available even if one instance or zone fails.
2. Scalability: Automatically scale your application up or down by adding or removing resources based on demand.
3. Fault Tolerance: Automatically route traffic away from unhealthy instances to healthy ones, ensuring that your application remains reliable.
4. Cost Optimization: Prevent over-provisioning of resources by ensuring that you have just the right number of resources running based on traffic levels.

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How to Set Up AWS Load Balancer: A Step-by-Step Guide

In this demo, we'll walk through setting up an Application Load Balancer for a simple web application.

Step 1: Create a Target Group

1. Open the AWS Management Console and navigate to EC2 > Load Balancing > Target Groups.
2. Click on Create target group.
3. Choose Instances as the target type and select HTTP as the protocol.
4. Give your target group a name and configure the health check settings (e.g., path /healthcheck for basic web applications).
5. Click Create.

Step 2: Create an Application Load Balancer

1. Navigate to the Load Balancers section under EC2.
2. Click Create Load Balancer and select Application Load Balancer.
3. Configure the Load Balancer with the following:
   • Name: Provide a unique name.
   • Scheme: Choose Internet-facing if you want it to be publicly accessible.
   • Listeners: Add an HTTP or HTTPS listener (choose HTTPS for secure traffic).
4. Choose the VPC and the availability zones where your EC2 instances are located.
5. Select the target group you created earlier for routing traffic.

Step 3: Configure Security Group

1. Create or select an existing security group that allows HTTP or HTTPS traffic (based on your listener).
2. Attach it to your load balancer.

Step 4: Test the Load Balancer

1. After your Load Balancer is created, it will have a DNS name (e.g., my-load-balancer-1234567890.us-west-2.elb.amazonaws.com).
2. Access the DNS name from your browser. If everything is configured correctly, traffic will be routed to your target instances.

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Best Practices for Using AWS Load Balancer

1. Use SSL/TLS Encryption: Always enable SSL/TLS for secure communication, especially for web applications.
2. Monitor with CloudWatch: Set up CloudWatch metrics to monitor the health of your load balancers and instances. Watch for latency, request count, and error rates.
3. Set Up Auto Scaling: Combine your load balancer with Auto Scaling groups to ensure that your resources scale up and down automatically with changing traffic demands.
4. Session Persistence: If your application requires sticky sessions, configure the load balancer to route requests from the same client to the same target.

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