Explanation: When a user is configuring ELB and registering the EC2 instances with it, ELB will create a sourcesecurity group. If the user wants to allow traffic only from ELB, he should remove all the rules set forthe other requests and open the port only for the ELB source security group. Reference: http://docs.aws.amazon.com/ElasticLoadBalancing/latest/DeveloperGuide/using-elbsecurity-groups.html