Question

How can I find out the instance id of an ec2 instance from within the ec2 instance?

Answer 1

On Amazon Linux AMIs you can do:

$ ec2-metadata -i instance-id: i-1234567890abcdef0

Or, on Ubuntu and some other linux flavours, ec2metadata --instance-id (This command may not be installed by default on ubuntu, but you can add it with sudo apt-get install cloud-utils)

As its name suggests, you can use the command to get other useful metadata too.

Answer 2

A curl or wget to http://169.254.169.254/latest/meta-data/instance-id will return you the instance id