PreheatJob: fix function lookups and iam function permission

[tongueroo]

This is a 🐞 bug fix.
This is a 🙋‍♂️ feature or enhancement.
This is a 🧐 documentation change.

• I've added tests (if it's a bug, feature or enhancement)
• I've adjusted the documentation (if it's a feature or enhancement)
• The test suite passes (run bundle exec rspec to verify this)

Summary

Fixes #440

Vaguely, kinda, sorta, somewhat remember this from years ago. It's was a bit tricky to implement as using Ref, GetAtt, or Sub to refer to a Lambda Function logical id within an inline IAM policy document results in CloudFormation complaining about a Circular Dependency. To get around this, need to create 2 separate CloudFormation resources: IAM::Role and a separate IAM::Policy. It’s interesting (annoying).

Also, notes:

• Improves prewarming and fixes bugs by looking up functions to preheat cloudformation, this generalizes it and handles long function names.
• Create separate IAM Role and Policy to allow policies to reference lambda function without a circular dependency error.
• This can to require a blue/green deployment. It depends if the user has user iam_policies in their code.

How to Test

Deploy an app with a name with a long enough name. IE:

Jets.application.configure do
  config.project_name = "some-very-very-really-long-super-long-app-project-name"
  # ...
end

Deploy it:

jets deploy

Confirm that really long function names that get cut off and managed by CloudFormation still produce an IAM policy that works.

Screenshots:

Version Changes

Major - due to need of blue/green deployments