Create write-metadata module. This module takes data from the various…

[joe-usa-amzn]

Proposed Commit Message

<feat>(amazon): Create write-metadata module.

Create write-metadata module. This module takes data from the various metadata services and writes them to files.
Add tests for write_metadata module and dictpath utility function

We would like to contribute this module to cloud-init because it is used in EC2 to write DNF vars (/etc/dnf/vars) in Amazon Linux to write region, domain, etc from metadata. It is enabled only for 'amazon' but all distros are able to use this.

Merge type

• Squash merge using "Proposed Commit Message"
• [] Rebase and merge unique commits. Requires commit messages per-commit each referencing the pull request number (#<PR_NUM>)

[holmanb]

Thanks for this proposal @joe-usa-amzn. Some initial questions.

What is this used for on Amazon Linux?

What can this accomplish that cannot be done using a jinja template and instance-data variables?

[joe-usa-amzn]

Thanks, checking to see if anything we introduced is duplicative or not.

[blackboxsw]

Given the examples in tests, it seems like this could be solved by something like:

## template: jinja
#cloud-config
write_files:
  - path: /etc/cloud/region
    content: {{ v1.region }}


# Or filters in jinja which can provide defaults if keys don't exist
write_files:
  - path: /etc/cloud/region
    content: {{ v1.region|default("no region set") }}

# Or conditionals to avoid writing files if you don't have a key
{% if 'region' in v1 %}
write_files:
  - path: /etc/cloud/region
    content: "we've got a region"
{% endif %}

Cloud-init's treatment Jinja syntax and behavior is easily testable on the command line with cloud-init query --format '{{ v1 }} or any other jinja constructs'

[joe-usa-amzn]

Right, we found this to work with RHEL 10 with v24.4 so it should technically work on AL (v22.2.2) when we upgrade. This code has been in our "fork" of cloud-init since v19.3.

## template: jinja
#cloud-config
write_files:
- content: |
    {{ ds.meta_data.placement.region }}
  path: /etc/dnf/vars/awsregion
  append: false

[joe-usa-amzn]

Closing this out as other modules provide the same features.