Application Loadbalancer Ip

Question

Hi, I see While creating Loadbalancer, We need minimum two public subnets. Once LB is created, it shows me two IPs of LB Dns URL. Ex -

non-authoritative answer:
Name:   Lb1LoadBalancer-405154402.eu-west-1.elb.amazonaws.com
Address: 54.228.29.194
Name:   Lb1LoadBalancer-405154402.eu-west-1.elb.amazonaws.com
Address: 52.30.70.94

Does it mean these Public Ips are one from each Public Subnet ( or Availability zones) . I also tried using three Availability zones ( Each zone has Public Subnet) . But still DNS only shows Two Public Ips of LB Url. I was expecting it to show 3 Addresses. But it doesn't show that way. Is anything wrong with my understanding ? What will happen if one AZ goes down, Will the DNS still show two Ips ? I am confused. 
Any  one knows ?

Answer

Hi, for each AZ you configured the ALB will provision an Elastic Network Interface (ENI) in the corresponding subnet you've selected, and it will assign a private IP as well as a public IP address for the ENI.

You could find all the ALB ENI and its public/private IP information at **"EC2" > "Network & Security"  > "Network Interfaces"**. However please note that for the ALB to provision an ENI in a particular AZ, you need at least one instance (belongs to that AZ) configured in the ALB target group. I suspect you didn't have an instance in the 3rd AZ or was not configured in the target group, and so ALB didn't provision an ENI in that AZ and hence you are not getting the 3rd IP in the DNS response.

Application Loadbalancer Ip

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