title: AWS Instance Only Allow Traffic From Load Balancer
body: <p>I have a Load Balancer and Auto-Scaling Group. The Load Balancer sends traffic to my Auto-Scaling Group. I have two instances: Instance 7000 (which is listening on port 7000 and is part of the auto-scaling group and gets its traffic from the load balancer) and Instance 8545 (which is listening on port 8545 and is simply a single instance that is not part of the Load Balancer or the Auto-Scaling Group).</p>
  
  <p>I have a load balancer security group ("LB-SG") and a security group for Instance 8545 ("App-SG"). I want Instance 8545 to only allow traffic from Instances that are part of the Load Balancer / Auto-Scaling Group. So I included "LB-SG" as an inbound rule for "App-SG" on port 8545 but it is not working. However, if I simply include the IP address for Instance 7000 on port 8545 as an inbound rule in "LB-SG" it works perfectly. But that doesn't solve my issue because if more instances get added by the Auto-Scaling Group or IP address changes then it won't work.</p>
  
  <p>Edit: reworded for clarity</p>