CODEWITHSUNDEEP
amazon-web-servicesamazon-ec2dns
user1788294
user1788294

Reputation: 1893

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

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.

Upvotes: 19

Views: 25986

Answers (5)

Gert van den Berg
Gert van den Berg

Reputation: 2786

Note: This is for Instance Metadata v1. It should be possible with v2 as well, but the URLs / process might differ somewhat...

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)

Upvotes: 12

matt burns
matt burns

Reputation: 25420

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

Where i-12abc34 is your instance id

Upvotes: 27

Paul Sheldrake
Paul Sheldrake

Reputation: 7821

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

Upvotes: 4

Lan
Lan

Reputation: 6640

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.

Upvotes: 0

Ben Whaley
Ben Whaley

Reputation: 34426

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.

Upvotes: 7

Related Questions