如何解析 AWS EC2 的主机名

Question

I try to access a service in an AWS EC2 I installed. It showed error:

do not know what is ip-10-124-123-122

How to resolve the private hostname of the EC2: ip-10-124-123-122 ?

This two links show I can change hostname of the ip-10-124-123-122 to the domain name of the EC2:

1. set enableDnsHostnames and enableDnsSupport to true in VPC: Using DNS with Your VPC - Amazon Virtual Private Cloud

2. change hostname from ip-10-124-123-122 to domainname : Changing the Hostname of Your Linux Instance - Amazon Elastic Compute Cloud

Note I do have a domain name for the webserver of EC2:port 80 but it is nothing to do with the hostname of the EC2. Because I created the domain name using this way:

https://domainname->route53->ALB:443->targetgroup->EC2 port 80. 

Note: the EC2 is in a non-default VPC and the VPC already has DNS resolution and DNS hostnames enabled.

If I type nslookup ip-10-XXX.region.compute.internal at an EC2 in the same subnet of that EC2, I can see the IP but the IP of that EC2 is not resolved.

If I type nslookup ip-10-XXX.region.compute.internal in my machine where I try to access the service;

Note: if I nslookup ip-10-124-123-122 won't get EC2 resolved. maybe this is the reason?

Are the above steps enough to resolve the hostname of the EC2? if not. how to resolve the error: do not know what is ip-10-124-123-122 ?

Answer 1

Each Amazon EC2 instance has a Public DNS Name and a Private DNS Name .

The Public DNS Name will look something like this:

ec2-54-252-207-11.ap-southeast-2.compute.amazonaws.com

This can be resolved on the Internet. It will actually be resolved to 54.252.207.11 as suggested by the name.

The Private DNS Name will look something like this:

ip-172-31-10-201.ap-southeast-2.compute.internal

It will be resolved to 172.31.10.201 .

The private DNS Name can only be resolved within the VPC where it exists . This is because the IP address only makes sense within that private network.

From a computer on the Internet, I can resolve the public address:

$ nslookup ec2-54-252-207-77.ap-southeast-2.compute.amazonaws.com
Server:     192.168.1.1
Address:    192.168.1.1#53

Non-authoritative answer:
Name:   ec2-54-252-207-77.ap-southeast-2.compute.amazonaws.com
Address: 54.252.207.77

From an Amazon EC2 instance within the same VPC, I can resolve the internal IP address:

$ nslookup ip-172-31-10-201.ap-southeast-2.compute.internal
Server:     172.31.0.2
Address:    172.31.0.2#53

Non-authoritative answer:
Name:   ip-172-31-10-201.ap-southeast-2.compute.internal
Address: 172.31.10.201

Bottom line: It appears you are not using the full DNS Name , which is why it is not working for you. This is like trying to resolve facebook instead of facebook.com . It will not work. (Well, it will if you define a default network search domain, but that's not really suitable here.)