CODEWITHSUNDEEP
bashamazon-ec2ec2-amiec2-api-tools
Reed
Reed

Reputation: 1638

shell script to set amazon ec2 hostname from tags

I am trying to set amazon EC2 hostname from the tag "Name"

And found the answer to extract tags from instance data.

ec2-describe-tags \
  --filter "resource-type=instance" \
  --filter "resource-id=$(ec2-metadata -i | cut -d ' ' -f2)" \
  --filter "key=Name" | cut -f5

the result is:

+------------+--------------+------+--------+
| resourceId | resourceType | key  | value  |
+------------+--------------+------+--------+
| i-1xxxxxxx | instance     | Name | dev200 |
+------------+--------------+------+--------+

I can see that I am almost there, but how do I get the value(dev200) from the result above? Then I can use it in:

echo $HOSTNAME > /etc/hostname

p.s. I have BASH on the instance, but I am completely lost in the bash document. can someone point me to the correct paragraph?

Upvotes: 2

Views: 7083

Answers (3)

Piotr Kuligowski
Piotr Kuligowski

Reputation: 1

Another way to get name tag is below.

hostname=$(aws ec2 describe-tags \
    --filters "Name=resource-id,Values=$(curl http://169.254.169.254/latest/meta-data/instance-id)" \
    --query 'Tags[?Key==`Name`].Value' \
    --output text)

And then you can set the hostname using hostnamectl.

hostnamectl set-hostname "$hostname"

Upvotes: 0

Dennis
Dennis

Reputation: 757

You could just use curl, since it is usually installed.

assigned_host_name=$(curl 'http://169.254.169.254/latest/meta-data/assigned_host_name') assigned_domain_name=$(curl 'http://169.254.169.254/latest/meta-data/assigned_domain_name')

Then just check that the values assigned don't contain a 404 HTML message like below.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <head> <title>404 - Not Found</title> </head> <body> <h1>404 - Not Found</h1> </body> </html>

Thenn do whatever magic you want to assign hostname. I'll edit this later today to add how I did that.

Upvotes: 0

Reed
Reed

Reputation: 1638

After some error and trial, got the script working:

#!/bin/bash
hostname=`ec2-describe-tags --filter "resource-type=instance" \
  --filter "resource-id=$(ec2-metadata -i | cut -d ' ' -f2)" \
  --filter "key=Name" | grep Name`

IFS="|" read -ra NAME <<< "$hostname"
hostname=${NAME[4]}
echo $hostname

Used IFS to get the string parsed into arrays, and luckily I know the 4th element is always the hostname.

EDIT (20-DEC-2012): In the short time since this was posted, several of the relevant ec2 command line tools have been modified, and flags changed or deprecated (e.g., the -i flag from above no longer seems to work on the current version of ec2metadata). Bearing that in mind, here is the command line script I used to get the current machine's "Name" tag (can't speak to the rest of the script):

ec2-describe-tags --filter "resource-type=instance" --filter "resource-id=$(ec2metadata --instance-id)" | awk '{print $5}'

On Debian/Ubuntu, you need to apt-get install cloud-utils ec2-api-tools to get these working (the later is only on Ubuntu Multiverse).

Upvotes: 4

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