Adds the specified instances to the specified load balancer.
The instance must be a running instance in the same network as the load
balancer (EC2-Classic or the same VPC). If you have EC2-Classic
instances and a load balancer in a VPC with ClassicLink enabled, you can
link the EC2-Classic instances to that VPC and then register the linked
EC2-Classic instances with the load balancer in the VPC.
Note that RegisterInstanceWithLoadBalancer completes when the request
has been registered. Instance registration takes a little time to
complete. To check the state of the registered instances, use
describe_load_balancers or
describe_instance_health.
After the instance is registered, it starts receiving traffic and
requests from the load balancer. Any instance that is not in one of the
Availability Zones registered for the load balancer is moved to the
OutOfService state. If an Availability Zone is added to the load
balancer later, any instances registered with the load balancer move to
the InService state.
To deregister instances from a load balancer, use
deregister_instances_from_load_balancer.
For more information, see Register or De-Register EC2 Instances
in the Classic Load Balancers Guide.