What do you call variables like "%(ec2_region)" in my cloud-init?

Question

What do you call these variables in my cloud-init file,

- http://%(ec2_region)s.ec2.ports.ubuntu.com/ubuntu-ports/
- http://%(availability_zone)s.clouds.ports.ubuntu.com/ubuntu-ports/
- http://%(region)s.clouds.ports.ubuntu.com/ubuntu-ports/

You can see here variables like %(region) are these available to all things in cloud-init? Where are these documented?

Answer 1

This is called instance metadata. Cloud providers expose metadata to cloud instances which cloud-init then stores and can be used in a few different contexts, such as jinja-templated cloud-init userdata.

Cloud-init instance metadata is documented here: https://cloudinit.readthedocs.io/en/latest/topics/instancedata.html