Get public dns name of a ec2 instance using ec2 command line tools in bash

Question

I have name of the a ec2 instance and want to do ssh to it. How can I figure out the 'Public DNS' of the ec2 instance using the ec2 instance name.

I want to do it using bash.

What do you mean by "I have name of ec2 instance"?. In ec2, name is nothing but a tag assigned to instance. — slayedbylucifer, Apr 02 '14 at 14:58

score 26 · Answer 1 · answered May 29 '15 at 18:33

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aws ec2 describe-instances --instance-ids i-12abc34 --query 'Reservations[].Instances[].PublicDnsName'

Where i-12abc34 is your instance id

answered May 29 '15 at 18:33

matt burns

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score 9 · Answer 2 · answered Sep 25 '19 at 14:06

You can query the instance metadata service.

Using curl:

curl -s http://169.254.169.254/latest/meta-data/public-hostname

Using wget:

wget -qO - http://169.254.169.254/latest/meta-data/public-hostname

If brave, actual bash:

exec 3<> /dev/tcp/169.254.169.254/80
echo -e "GET /latest/meta-data/public-hostname HTTP/1.0\r\n\r\n" >&3
cat <&3

(The last one leaves the connection open for me, so the cat gets stuck. The headers are also present in the output)

(This is from the instance itself and need access to the instnace - it is not the instance name-related version. There are enough of those answers here)

@Geoff Still works for me. Is IMDSv1 enabled on the instance? (I'll need to check if a v2 version exists) — Gert van den Berg, Jun 12 '21 at 22:02

score 7 · Answer 3 · answered Apr 02 '14 at 17:19

7

Using the EC2 API tools:

# Region is only needed if not in us-east-1
$ ec2-describe-instances --region <region> <instance id>

Using the unified AWS CLI tool:

$ aws --region <region> ec2 describe-instances --instance-ids <instance id≥

I prefer the unified tool as it offers comprehensive and consistent data.

answered Apr 02 '14 at 17:19

Ben Whaley

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You can further restric the ouput to Public DNS name only using the ```--query``` parameter, like this ```--query "Reservations[].Instances[].PublicDnsName"``` – Sébastien Stormacq Apr 02 '14 at 18:55

score 4 · Answer 4 · edited May 23 '17 at 12:25

4

If you install the cloud-utils tool as described in this answer it's much more straight forward.

https://stackoverflow.com/a/10600619/28672

ec2-metadata --public-ipv4
> public-ipv4: 54.200.4.52

edited May 23 '17 at 12:25

Community

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answered Aug 12 '14 at 11:04

Paul Sheldrake

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and equivalently: ec2-metadata --public-hostname, for the hostname – j__ May 10 '21 at 11:56

score 0 · Answer 5 · answered Apr 02 '14 at 17:46

It depends on what you mean by "figure out". If you mean figuring out yourself, you cannot. The public DNS name has nothing to do with the ec2 instance name. The public DNS name is composed of public IP address, region/availability zone, type of service, aws domain name, etc. For example, ec2-xx-xxx-x-xx.us-west-2.compute.amazonaws.com. Because the public IP address is changed every time you stop and start your instance, unless you use an elastic IP address, your public DNS name will be changed.

If you mean figure out by using AWS API or CLI tool, you can. Using EC2 CLI, you should use command ec2-describe-instances instance_id. Again, the instance has to be running and the public DNS does change after stop/start.

Get public dns name of a ec2 instance using ec2 command line tools in bash

5 Answers5