Refactor module_utils/elbv2 listeners and rules comparison

[Helen Bailey]

Summary

Note: this is not really a new feature but I wanted to create an issue for this work so we can track it.

The elbv2 logic around comparing listeners and listener rules is quite complex, which is unsurprising as the AWS logic is also complex. However, as it is currently written it's very difficult to understand what each of these comparisons is doing. In some cases, methods have been updated over time to fix bugs but the method names and docstrings haven't changed. This makes it prone to errors (see #1877, #1284) and difficult to review new bugfixes. I propose we refactor this with an eye to making our code easier to understand, in particular:

• Documenting what is the AWS logic/requirements we are trying to enforce when creating or modifying a listener/rule (note that the requirements for creating vs. modifying are not the same).
• Ensuring that methods/functions have type hints so it's clear what a given method returns.
• Adding documentation to each method to clarify what it does.
• Thinking about whether we can break any of these methods down into smaller, more discrete comparison methods with simpler tests.
• Ensuring we have unit tests covering all the logic we are trying to enforce.

Issue Type

Feature Idea

Component Name

module_utils/elbv2

Additional Information

Refactoring this code would make it easier to maintain, as it is currently challenging to understand and modify.

Code of Conduct

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