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I can get the internal hostname of an instance with the hostname command. How do I get the external host name from within the instance?

Specifically I'm on EY and using the ey ssh command, I want to know what the host name is so I can pass this to scp.

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6 Answers 6

Reset to default
13

From within the instance, you can hit the Instance Metadata Service:

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

or

curl http://instance-data.ec2.internal/latest/meta-data/public-hostname

A wide variety of data is available via this interface.

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5
  • curl: (6) Could not resolve host: instance-data.ec2.internal
    – Peter Kionga-Kamau
    Jun 28, 2023 at 18:37
  • @PeterKionga-Kamau And did you try the IP-based approach?
    – ceejayoz
    Jun 30, 2023 at 17:58
  • No, IPs change and can't be relied upon indefinitely. Ended up using a combination of ec2metadata and nslookup
    – Peter Kionga-Kamau
    Jul 1, 2023 at 21:46
  • 1
    @PeterKionga-Kamau 169.254.169.254 isn't likely to change on the AWS end.
    – ceejayoz
    Jul 1, 2023 at 23:34
  • It doesn't matter how unlikely it is, if it is possible and it is avoidable then it is an unnecessary failure point.
    – Peter Kionga-Kamau
    Jul 2, 2023 at 20:37
7

/opt/aws/bin/ec2-metadata -p will print the public hostname of that instance.

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1
  • -bash: /opt/aws/bin/ec2-metadata: No such file or directory - Instead use ec2metadata --public-hostname as described by @calvin-huang below
    – Peter Kionga-Kamau
    Jun 28, 2023 at 18:37
4

It is very simple by ec2 instance metadata query tool.

run command:

./ec2-metadata --public-ipv4

or:

./ec2-metadata --public-hostname

for more information, just pass --help to ec2-metadata

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1
  • -bash: ./ec2-metadata: No such file or directory instead use ec2metadata --public-hostname as described by @calvin-huang below
    – Peter Kionga-Kamau
    Jun 28, 2023 at 18:38
2

Currently, on EC2 instances you can use:

$ ec2metadata --public-hostname
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1

I don't know what system you use but I assume a Linux. You can either connect directly to your IP address or try a reverse lookup of this ip with for example

host -a <ip_address>

You can find out your IP address if you use the command ifconfig that will print out all information on the network interfaces.

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1
  • If the host name is unknown, it is highly likely that the IP address is also unknown (at least, by whatever script is trying to find it).
    – Peter Kionga-Kamau
    Jun 28, 2023 at 18:39
0 
public_hostname=$(timeout 2 ec2metadata --public-hostname 2> /dev/null)
if [ -z "$public_hostname" ]; then # fallback to nslookup + hostname
    public_hostname=$(nslookup "$(hostname -I | awk '{print $1}')" | awk '/name/{print $NF}' | sed 's/\.$//')
fi
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