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Amazon Web Services (AWS) provides Elastic Load Balancing to automatically distribute incoming web traffic across multiple Amazon Elastic Compute Cloud (Amazon EC2) instances. With Elastic Load Balancing, you can add and remove EC2 instances as your needs change without disrupting the overall flow of information. If one EC2 instance fails, Elastic Load Balancing automatically reroutes the traffic to remaining running EC2 instances. If the failed EC2 instance is restored, Elastic Load Balancing restores the traffic to that instance. Elastic Load Balancing offers clients a single point of contact, and it can also serve as the first line of defense against attacks on your network. You can offload the work of encryption and decryption to the Elastic Load Balancing, so your servers can focus on their main task.
When you use Elastic Load Balancing to manage traffic to your application, you get the following benefits:
Distribution of requests to Amazon EC2 instances (servers) in multiple Availability Zones in a way that minimizes the risk of overloading one single instance. And if an entire Availability Zone goes offline, Elastic Load Balancing routes traffic to instances in other Availability Zones.
Continuous monitoring of the health of Amazon EC2 instances registered with the load balancer so that requests are sent only to the healthy instances. If an instance becomes unhealthy, Elastic Load Balancing stops sending traffic to that instance and spreads the load across the remaining healthy instances.
Support for end-to-end traffic encryption on those networks that use secure (HTTPS/SSL) connections.
The ability to take over the encryption and decryption work from the Amazon EC2 instances, and manage it centrally on the load balancer.
Support for the sticky session feature, which is the ability to "stick" user sessions to specific Amazon EC2 instances.
Association of the load balancer with your domain name. Because the load balancer is the only computer that is exposed to the Internet, you don’t have to create and manage public domain names for the instances that the load balancer manages. 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.
When used in an Amazon Virtual Private Cloud (Amazon VPC), support for creation and management of security groups associated with your load balancer to provide additional networking and security options.
Support for use of both Internet protocol version 4 (IPv4) and Internet protocol version 6 (IPv6).
As with all Amazon Web Services, you pay only for what you use. For Elastic Load Balancing, you pay for each hour or portion of an hour that the service is running, and you pay for each gigabyte of data that is transferred through your load balancer. For current pricing information for Elastic Load Balancing, go to Elastic Load Balancing Pricing.
If you are a new AWS customer, you are eligible to use the free usage tier for twelve months following your AWS sign-up date. The free tier includes 750 hours per month of Amazon EC2 micro instance usage, and 750 hours per month of Elastic Load Balancing, plus 15 GB of data processing. For information about the free usage tier, go to AWS Free Usage Tier.