Amazon ELB

What Is Elastic Load Balancing?

Elastic Load Balancing automatically distributes incoming traffic across multiple EC2 instances. You create a load balancer and register instances with the load balancer in one or more Availability Zones. The load balancer serves as a single point of contact for clients. This enables you to increase the availability of your application. You can add and remove EC2 instances from your load balancer as your needs change, without disrupting the overall flow of information. If an EC2 instance fails, Elastic Load Balancing automatically reroutes the traffic to the remaining running EC2 instances. If a failed EC2 instance is restored, Elastic Load Balancing restores the traffic to that instance. Elastic Load Balancing can also serve as the first line of defense against attacks on your network. You can offload the work of encryption and decryption to your load balancer so that your EC2 instances can focus on their main work.

For more information, see Elastic Load Balancing.

Features of Elastic Load Balancing

Elastic Load Balancing provides the following features:

  • You can use the operating systems and instance types supported by Amazon EC2. You can configure your EC2 instances to accept traffic only from your load balancer.
  • You can configure the load balancer to accept traffic using the following protocols: HTTP, HTTPS (secure HTTP), TCP, and SSL (secure TCP).
  • You can configure your load balancer to distribute requests to EC2 instances in multiple Availability Zones, minimizing the risk of overloading one single instance. If an entire Availability Zone goes offline, the load balancer routes traffic to instances in other Availability Zones.
  • There is no limit on the number of connections that your load balancer can attempt to make with your EC2 instances. The number of connections scales with the number of concurrent requests that the load balancer receives.
  • You can configure the health checks that Elastic Load Balancing uses to monitor the health of the EC2 instances registered with the load balancer so that it can send requests only to the healthy instances.
  • You can use end-to-end traffic encryption on those networks that use secure (HTTPS/SSL) connections.
  • [EC2-VPC] You can create an Internet-facing load balancer, which takes requests from clients over the Internet and routes them to EC2 instances in your public subnets, or aninternal-facing load balancer, which takes requests from clients in your VPC and routes them to EC2 instances in your private subnets. Load balancers in EC2-Classic are always Internet-facing.
  • [EC2-Classic] Load balancers for EC2-Classic support both IPv4 and IPv6 addresses. Load balancers for a VPC do not support IPv6 addresses.
  • You can monitor your load balancer using CloudWatch metrics, access logs, and AWS CloudTrail.
  • You can associate your Internet-facing load balancer with your domain name. Because the load balancer receives all requests from clients, you don’t need to create and manage public domain names for the EC2 instances to which the load balancer routes traffic. You can point the instance’s domain records at the load balancer instead and scale as needed (either adding or removing capacity) without having to update the records with each scaling activity.



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