domain. The Amazon DNS servers return one or more IP addresses to the client. These are the IP addresses of the load balancer nodes for your load balancer. As traffic to your application changes over time, Elastic Load Balancing scales your load balancer and updates the DNS entry. Note that the DNS entry also specifies the time-to-live (TTL) as 60 seconds, which ensures that the IP addresses can be remapped quickly in response to changing traffic. The client uses DNS round robin to determine which IP address to use to send the request to the load balancer. The load balancer node that receives the request uses a routing algorithm to select a healthy instance. It uses the round robin routing algorithm for TCP listeners, and the least outstanding requests routing algorithm (favors the instances with the fewest outstanding requests) for HTTP and HTTPS listeners. The cross-zone load balancing setting also determines how the load balancer selects an instance. If cross-zone load balancing is disabled, the load balancer node selects the instance from the same Availability Zone that it is in. If cross-zone load balancing is enabled, the load balancer node selects the instance regardless of Availability Zone. The load balancer node routes the client request to the selected instance. AWS Training and Certification Appendix © 2018 Amazon Web Services, Inc. or its affiliates All rights reserved. 263
Before you start using Elastic Load Balancing, you must configure one or more listeners for your load balancer. A listener is a process that checks for connection requests. It is configured with a protocol and a port for front-end (client to load balancer) connections, and a protocol and a port for back-end (load balancer to back-end instance) connections. Elastic Load Balancing supports the following protocols: • HTTP • HTTPS (secure HTTP) • TCP • SSL (secure TCP) The HTTPS protocol uses the SSL protocol to establish secure connections over the HTTP layer. You can also use the SSL protocol to establish secure connections over the TCP layer. If the front-end connection uses TCP or SSL, your back-end connections can use either TCP or SSL. If the front-end connection uses HTTP or HTTPS, your back-end connections can use either HTTP or HTTPS. AWS Training and Certification Appendix © 2018 Amazon Web Services, Inc. or its affiliates All rights reserved. 264
After you've created your load balancer, you must register your EC2 instances with the load balancer. You can select EC2 instances from a single Availability Zone or multiple Availability Zones within the same region as the load balancer. Elastic Load Balancing routinely performs health checks on registered EC2 instances and automatically distributes incoming requests to the DNS name of your load balancer across the registered, healthy EC2 instances.
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- Summer '18
- Amazon Web Services, AWS, Amazon Elastic Compute Cloud