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The following diagram shows how the various components of the Elastic Load Balancing work together. The remainder of this section provides a step-by-step view of the flow of events that take place when a client requests a URL served by your applications.
This example assumes that you have created a load balancer, created a custom domain name and associated your load balancer with the domain name using a CNAME entry in DNS, and have registered your instances with it.
The client sends a URL request to DNS servers to access your application. The DNS server responds with a DNS name. For example, myLB-1234567890.us-east-1.elb.amazonaws.com.
The client looks for the resolution of the DNS name sent by the DNS server. The DNS entry is controlled by Amazon because your application instances are under the amazonaws.com domain. The Amazon DNS servers return one or more IP addresses.
The client then opens a connection to the machine at the provided IP address. The instance at this address is the load balancer you created.
The load balancer checks the health states of all the registered EC2 application instances within the selected Availability Zones and will begin routing trafic to instances that have met the healthy threshold defined in the health check configuration.
The load balancer routes the client request to the healthy EC2 application instance identified in the previous step. At this point, the client is communicating with one of your EC2 instances through your load balancer. The load balancer listeners can be configured to use either HTTP, HTTPS, TCP, or SSL protocols for both front-end connection (client to load balancer) and back-end connection (load balancer to back-end instance).
Amazon Route 53 is AWS's highly available and cost-effective DNS service. Using Amazon 53's Alias records will provide performance improvements because the clients will need only to make a single request to resolve the domain name. Also, queries to Alias records are free of charge.
You can access and work with your load balancer using one of the following interfaces:
AWS Management Console—A simple web-browser interface that you can use to create and manage your load balancers without using additional software or tools. On the AWS site, you can open the console by clicking Sign in to the AWS Console.
Command Line Interfaces (CLI)—A Java-based command-line client that wraps the SOAP API.
Programmatic Interface— SDKs provided by AWS, third-party libraries, and Elastic Load Balancing Query API.
For information on installing and using the command line interfaces, Query APIs, and SDKs provided by AWS, see Get Set Up with Elastic Load Balancing Interfaces.