# How to support diff mode with keeping backward compatibilities?

**URL:** <https://forum.ansible.com/t/how-to-support-diff-mode-with-keeping-backward-compatibilities/28079>\
**Category:** Ansible Developer\
**Created:** [July 18, 2018, 10:50am UTC](https://forum.ansible.com/t/how-to-support-diff-mode-with-keeping-backward-compatibilities/28079 "2018-07-18T10:50:36Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![hitsumabushi1](https://avatars.discourse-cdn.com/v4/letter/h/b9bd4f/32.png) [@hitsumabushi1](https://forum.ansible.com/u/hitsumabushi1)\
**Post date:** [July 18, 2018, 10:50am UTC](https://forum.ansible.com/t/how-to-support-diff-mode-with-keeping-backward-compatibilities/28079/1 "2018-07-18T10:50:36Z")

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Hi,

I’ve currently used vyos\_config module and, for CI/CD, I want to get config differences before applying.

However, vyos\_config doesn’t output config diffs, even in diff mode.

For outputting diff, the module has to store dict in ‘diff’ key, and the dict must have (‘before’, ‘after’) or ‘prepared’ keys.  
I made PR ( [https://github.com/ansible/ansible/pull/42494](https://github.com/ansible/ansible/pull/42494) ), but vyos\_config use ‘diff’ key in another way.

My PR breaks backward compatibility.

Is there any workaround for keeping backward compatibility in this situation?