How to use "Instance ID" in cloud-config.yml on CoreOS on EC2?

Question

I have CoreOS instances on Amazon EC2.

There are some pre-defined variables accessible from cloud-config.yml such as "$private_ipv4" or "$public_ipv4".

Is there a way to access "Instance ID" of EC2 instances like "$instance_id"? (I have tried "$instance_id" and "$INSTANCE_ID" but neither of them took effect)

score 3 · Accepted Answer · answered Aug 20 '15 at 19:29

3

That variable isn't built in, but you could do one of two things:

curl the metadata service for that value directly:

curl http://169.254.169.254/latest/meta-data/instance-id

have a "oneshot" unit write out a the result of that curl to a file and then source that file in your units, just like you can for environment info.

The oneshot unit one would write INSTANCE_ID=abc123 to /etc/instance-id and your regular unit would depend on the oneshot (Requires=instanceid.service/After=instanceid.service) contains EnvironmentFile=/etc/instance-id, which would make $INSTANCE_ID available for use in a unit.

More docs on using env vars in units: https://coreos.com/os/docs/latest/using-environment-variables-in-systemd-units.html#environmentfile-directive

answered Aug 20 '15 at 19:29

Rob

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Thank you Rob! It really helps :-) – ai0307 Aug 21 '15 at 01:24
I'm confused by this. The cloudinit docs seem to say differently. http://cloudinit.readthedocs.io/en/latest/topics/examples.html#run-commands-on-first-boot – voutasaurus Jun 07 '16 at 21:12
Also: http://cloudinit.readthedocs.io/en/latest/topics/examples.html#call-a-url-when-finished – voutasaurus Jun 07 '16 at 21:13
In practice I have the same issue. $INSTANCE_ID does not seem to be defined. – voutasaurus Jun 07 '16 at 21:14
CoreOS' version of cloud-init only supports a subset of the entire cloud-init spec. The only variables that are supported are the IP addresses. – Rob Jun 08 '16 at 21:50

How to use "Instance ID" in cloud-config.yml on CoreOS on EC2?

1 Answers1