What is AWS Elastic Load Balancing (ELB)?

AWS Elastic Load Balancing (ELB) is a managed service provided by Amazon Web Services (AWS) that distributes incoming network traffic across multiple Amazon EC2 instances to ensure high availability, fault tolerance, and efficient use of resources. ELB automatically scales and redirects traffic to healthy instances, making it an essential component for building highly available and reliable web applications. There are two types of Elastic Load Balancers in AWS:

1. Application Load Balancer (ALB): An Application Load Balancer is a Layer 7 load balancer that operates at the application layer of the OSI model. It is designed to route traffic based on application-level content, such as HTTP/HTTPS requests. ALB is ideal for applications that require advanced routing, content-based routing, and support for multiple domains and certificates. It also supports path-based routing, content-based routing, and host-based routing.

2. Network Load Balancer (NLB): A Network Load Balancer is a Layer 4 load balancer that operates at the transport layer. It is designed for applications that require high levels of performance and low latency. NLB is capable of handling millions of requests per second and is suitable for TCP, UDP, and TLS (Transport Layer Security) traffic.

Key Features and Use Cases:

1. High Availability: ELB automatically distributes incoming traffic across multiple healthy instances, ensuring that applications remain available and responsive even if some instances fail.

2. Auto Scaling: ELB works seamlessly with Auto Scaling groups, allowing you to automatically adjust the number of instances based on traffic demand. When new instances are launched, ELB routes traffic to them.

3. Health Checks: ELB performs health checks on instances to determine their availability. If an instance fails a health check, ELB automatically stops sending traffic to it until it passes the health check.

4. SSL/TLS Termination: ELB can handle SSL/TLS termination, offloading the decryption of SSL/TLS traffic from the backend instances. This reduces the computational load on instances and improves security.

5. Path and Host-Based Routing (ALB): Application Load Balancers support advanced routing based on the request path and host header. This allows you to route traffic to different target groups based on URL paths and domain names.

6. WebSockets Support (ALB): ALB supports WebSocket connections, making it suitable for real-time applications and chat applications.

7. Container Load Balancing: ELB is suitable for load balancing containers in Amazon ECS and Kubernetes clusters, distributing traffic to containers within a cluster.

8. Global Accelerator: AWS Global Accelerator is a service that uses ELB as one of its endpoints. It routes traffic to the optimal AWS endpoint (typically an Application Load Balancer) based on health, geography, and routing policies.

AWS Elastic Load Balancing is an essential component for building scalable, fault-tolerant, and high-performance web applications in the AWS cloud. It simplifies the management of traffic distribution and ensures that applications remain available and responsive to user requests. Customers can choose between Application Load Balancers and Network Load Balancers based on their specific traffic routing and performance requirements.