Table of Contents
Elastic Load Balancing
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Definition and Purpose
Elastic Load Balancing (ELB) is a service provided by Amazon Web Services (AWS) that automatically distributes incoming application traffic across multiple targets, such as EC2 instances, containers, IP addresses, and Lambda functions. The primary purpose of ELB is to ensure fault tolerance and high availability for applications by balancing the load across different resources, preventing any single resource from being overwhelmed.
Types of Elastic Load Balancers
AWS offers three main types of load balancers under the ELB service:
1. **Application Load Balancer (ALB)**: Best suited for web applications, ALB operates at the application layer (Layer 7 of the OSI model). It can make routing decisions based on content, such as URLs or headers, enabling advanced features like host-based and path-based routing.
2. **Network Load Balancer (NLB)**: Ideal for applications that require ultra-low latency and handle millions of requests per second, NLB operates at the transport layer (Layer 4 of the OSI model). It is designed to manage TCP, UDP, and TLS traffic, making it suitable for extreme performance needs.
3. **Classic Load Balancer (CLB)**: This is the original ELB and operates at both the transport layer (Layer 4) and the application layer (Layer 7). While it still exists for backward compatibility, most new applications use either ALB or NLB.
How Elastic Load Balancing Works
ELB works by creating a load balancer that serves as the single point of entry for your application. When a client makes a request, the load balancer receives it and determines the best target to forward the request to based on predefined routing rules. The load balancer continuously monitors the health of its targets, ensuring that traffic is only routed to healthy instances.
Health Checks
ELB performs health checks on its registered targets to ensure they are functioning correctly. If a target fails a health check, ELB will stop sending traffic to that target until it passes the health check again. This ensures that traffic is only routed to healthy instances, maintaining the availability of your application.
Scalability and Fault Tolerance
One of the significant benefits of using ELB is its ability to automatically scale based on traffic demand. ELB can handle the load during peak traffic times and reduce capacity when demand is low, optimizing resource usage and cost. Additionally, by distributing traffic across multiple targets, ELB provides fault tolerance, minimizing the risk of application downtime.
Integration with Auto Scaling
ELB works seamlessly with AWS Auto Scaling, allowing you to automatically add or remove instances based on traffic patterns. This integration ensures that your application has enough resources to handle varying levels of traffic, improving both performance and cost-efficiency.
Security Features
ELB provides several security features to help protect your application. It supports TLS termination, allowing you to offload the decryption process from your application instances to the load balancer. ELB also integrates with AWS Certificate Manager (ACM) for easy management of SSL/TLS certificates. Additionally, ELB can work with AWS Web Application Firewall (WAF) to protect your application from common web exploits.
Monitoring and Logging
AWS offers extensive monitoring and logging capabilities for ELB. You can use Amazon CloudWatch to track metrics such as request count, latency, and error rates. ELB also provides access logs that contain detailed information about requests sent to your load balancer, which can be stored in Amazon S3 for further analysis.
Cross-Zone Load Balancing
Cross-zone load balancing is a feature that allows ELB to distribute traffic evenly across all registered targets in all enabled AWS Availability Zones. This feature ensures that even if some Availability Zones have fewer resources, the load is balanced across the entire region, improving application resilience.
Sticky Sessions
Sticky sessions, or session affinity, is a feature that enables ELB to bind a user session to a specific target. This is useful for applications that require a user to consistently interact with the same backend server. ELB accomplishes this by inserting a special cookie into the user's browser, which the load balancer uses to direct subsequent requests to the same target.
IP Address-Based Targeting
NLB supports IP address-based targeting, allowing you to register targets outside of AWS. This feature is useful for hybrid environments where your application may consist of both AWS and on-premises resources. NLB can route traffic to any IP address, providing greater flexibility in designing your application's architecture.
Lambda Function Support
ALB and NLB support AWS Lambda functions as targets. This means you can directly route traffic to a Lambda function without needing an EC2 instance or other infrastructure. This feature is particularly useful for serverless architectures, where you want to reduce infrastructure management overhead.
Pricing
ELB pricing is based on the number of hours that the load balancer is running and the amount of data processed by the load balancer. Costs can vary depending on the type of load balancer and the region in which it is deployed. AWS provides a pricing calculator to help estimate costs based on expected usage.
Use Cases
- **Web Applications**: ALB is commonly used for web applications that require advanced routing and security features. - **Microservices**: ALB is well-suited for microservices architectures, where different services require different routing rules. - **High-Performance Applications**: NLB is ideal for applications that demand high performance and low latency. - **Legacy Applications**: CLB can be used for legacy applications that require both Layer 4 and Layer 7 load balancing.
Benefits of Elastic Load Balancing
ELB offers several key benefits, including improved application availability, automatic scaling, enhanced security, and simplified infrastructure management. By using ELB, organizations can ensure that their applications remain responsive and reliable, even under varying traffic conditions.
Getting Started
To get started with ELB, you can create a load balancer through the AWS Management Console, AWS CLI, or AWS SDKs. The process involves choosing the type of load balancer, configuring listeners and targets, setting up security groups, and optionally enabling features like health checks and sticky sessions.
Conclusion
Elastic Load Balancing is a critical component of modern application architectures on AWS. By distributing traffic across multiple targets, it ensures high availability, fault tolerance, and scalability for your applications. Whether you are running a small web application or a large-scale distributed system, ELB provides the necessary tools to manage and optimize your application's traffic.
- Snippet from Wikipedia: Amazon Elastic Compute Cloud
Amazon Elastic Compute Cloud (EC2) is a part of Amazon's cloud-computing platform, Amazon Web Services (AWS), that allows users to rent virtual computers on which to run their own computer applications. EC2 encourages scalable deployment of applications by providing a web service through which a user can boot an Amazon Machine Image (AMI) to configure a virtual machine, which Amazon calls an "instance", containing any software desired. A user can create, launch, and terminate server-instances as needed, paying by the second for active servers – hence the term "elastic". EC2 provides users with control over the geographical location of instances that allows for latency optimization and high levels of redundancy. In November 2010, Amazon switched its own retail website platform to EC2 and AWS.