A Minimum Viable CloudFormation Template2019-08-19
Sometimes when testing CloudFormation features I need a minimum viable template to try that feature with.
(Like my Ansible Minimum Viable Playbook).
Here’s the basic template I use:
It has two things:
The format version. This is one of the useless things in CloudFormation. They left a version specifier and then haven’t changed it for (at time of writing) 9 years.
But, I’m paranoid, so I make sure my templates have the version specifier just in case they release a breaking change. Just in case.
An SNS topic resource. I’ve found SNS topics are about the fastest resources to create or update, taking about 10 seconds.
I can then change it according to what I want to test, for example adding parameters, outputs, or referencing resources. This is easier and faster than testing as part of a larger CloudFormation template.
Testing a Bug
As an example, I used this template to test for an old bug.
Previously, if you changed a template to only add a
DeletionPolicy to a resource, CloudFormation would succeed but not actually add the policy.
Then if you deleted the stack, CloudFormation would delete the resource, even though you thought it wouldn’t.
I tested this in a minute with my MVP template. I created a stack from the above basic template, then updated it with this template:
The I deleted the stack and SNS retained the topic.
Nice to know AWS have fixed the bug, although I don’t recall it ever being publicly acknowledged, or mentioned on the release history.
Hope this helps you with testing CloudFormation!
Or perhaps you'd like to read a related post:
- Validating CloudFormation Templates With cfn-lint
- Running CloudFormation Drift Detection on All Your Stacks
- Testing Boto3 with Pytest Fixtures
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