Source By: <docs.aws.amazon.com>
What Is Elastic Load Balancing?
Elastic Load Balancing distributes incoming application traffic across multiple EC2 instances, in multiple Availability Zones. This increases the fault tolerance of your applications.
The load balancer serves as a single point of contact for clients, which increases the availability of your application. You can add and remove instances from your load balancer as your needs change, without disrupting the overall flow of requests to your application. Elastic Load Balancing scales your load balancer as traffic to your application changes over time, and can scale to the vast majority of workloads automatically.
You can configure health checks, which are used to monitor the health of the registered instances so that the load balancer can send requests only to the healthy instances. You can also offload the work of encryption and decryption to your load balancer so that your instances can focus on their main work.
Features of Elastic Load Balancing
Elastic Load Balancing supports two types of load balancers: Application Load Balancers and Classic Load Balancers. Choose the load balancer type that meets your needs.
| Feature | Classic Load Balancer | Application Load Balancer |
|---|---|---|
| Protocols | HTTP, HTTPS, TCP, SSL | HTTP, HTTPS |
| Platforms | EC2-Classic, EC2-VPC | EC2-VPC |
| Sticky sessions (cookies) | ✔ | load balancer generated |
| Back-end server authentication | ✔ | |
| Back-end server encryption | ✔ | ✔ |
| Idle connection timeout | ✔ | ✔ |
| Connection draining | ✔ | ✔ |
| Cross-zone load balancing † | ✔ | Always enabled |
| Health checks † † | ✔ | Improved |
| CloudWatch metrics | ✔ | Improved |
| Access logs | ✔ | Improved |
| Path-based routing | ✔ | |
| Route to multiple ports on a single instance | ✔ | |
| HTTP/2 support | ✔ | |
| Websockets support | ✔ | |
| Load balancer deletion protection | ✔ |
† Cross-zone load balancing is always enabled for an Application Load Balancer. For a Classic Load Balancer, it is disabled by default, but can be enabled and disabled as needed.
† † For an Application Load Balancer, you can specify the HTTP codes that indicate a successful health check response. An Application Load Balancer returns improved information about the cause of health check failures.
Accessing Elastic Load Balancing
You can create, access, and manage your load balancers using any of the following interfaces:
- AWS Management Console— Provides a web interface that you can use to access Elastic Load Balancing.
- AWS Command Line Interface (AWS CLI) — Provides commands for a broad set of AWS services, including Elastic Load Balancing, and is supported on Windows, Mac, and Linux.
- AWS SDKs — Provides language-specific APIs and takes care of many of the connection details, such as calculating signatures, handling request retries, and error handling.
- Query API— Provides low-level API actions that you call using HTTPS requests. Using the Query API is the most direct way to access Elastic Load Balancing, but it requires that your application handle low-level details such as generating the hash to sign the request, and error handling. For more information, see the following:
- Application Load Balancers — API version 2015-12-01
- Classic Load Balancers — API version 2012-06-01
Related Services
Elastic Load Balancing works with the following services to improve the availability and scalability of your applications.
- Amazon EC2 — Virtual servers that run your applications in the cloud. You can configure your load balancer to route traffic to your EC2 instances.
- Amazon ECS — Enables you to run, stop, and manage Docker containers on a cluster of EC2 instances. You can configure your load balancer to route traffic to your containers.
- Auto Scaling — Ensures that you are running your desired number of instances, even if an instance fails, and enables you to automatically increase or decrease the number of instances as the demand on your instances changes. If you enable Auto Scaling with Elastic Load Balancing, instances that are launched by Auto Scaling are automatically registered with the load balancer, and instances that are terminated by Auto Scaling are automatically de-registered from the load balancer.
- Amazon CloudWatch — Enables you to monitor your load balancer and take action as needed.
- Amazon Route 53 — Provides a reliable and cost-effective way to route visitors to websites by translating domain names (such as www.example.com) into the numeric IP addresses (such as 192.0.2.1) that computers use to connect to each other. AWS assigns URLs to your resources, such as load balancers. However, you might want a URL that is easy for users to remember. For example, you can map your domain name to a load balancer.
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