LISTENER:
1.) CHECKS FOR CONNECTION REQUESTS FROM CLIENTS, USING THE PROTOCOL AND PORT THAT YOU CONFIGURE.
2.) FORWARDS THOSE CONNECTION REQUESTS TO ONE OR MORE REGISTERED INSTANCES USING THE PROTOCOL AND PORT NUMBER THAT YOU CONFIGURE.
3.) YOU ADD ONE OR MORE LISTENERS TO YOUR LOAD BALANCER.
HEATH CHECKS:
YOUR CLASSIC LOAD BALANCER PERIODICALLY SENDS REQUESTS TO ITS REGISTERED INSTANCES TO TEST THEIR STATUS. THESE TESTS ARE CALLED HEALTH CHECKS.
The load balancer performs health checks on all registered instances, whether the instance is in a healthy state or an unhealthy state.
INSTANCE STATUS:
HEALTHY - THE STATUS OF THE INSTANCES THAT ARE HEALTHY AT THE TIME OF THE HEALTH CHECK IS INSERVICE.
OUTOFSERVICE - The status of any instances that are unhealthy at the time of the health check.
benefits - Using a Classic Load Balancer instead of an Application Load Balancer has the following benefits:
Support for EC2-Classic
Support for TCP and SSL listeners
Support for sticky sessions using application-generated cookies
***** With Classic Load Balancers, you register instances with the load balancer *****
To ensure that your registered instances are able to handle the request load in each Availability Zone, it is important to keep approximately the same number of instances in each Availability Zone registered with the load balancer.
For example, if you have ten instances in Availability Zone us-west-2a and two instances in us-west-2b, the requests are distributed evenly between the two Availability Zones.
As a result,
the two instances in us-west-2b serve the same amount of traffic as the ten instances in us-west-2a.
Instead, you should have six instances in each Availability Zone.
