📖 Improve plugin phase 1.5 EP

[Adirio]

While implementing plugin phase 1.5 and aligning operator-SDK, several additional concepts that were not designed at first have raised. This PR improved on the plugin phase 1.5 design document including those changes.

Plugin phase 1.5 will be useful to achieve several goals in kubebuilder. For example, plugin chaining allows to split monolithic plugins into smaller ones, and plugin bundles maintain backwards compatibility towards the user.

• Splitting non-go-related and go-related scaffolding so that plugins for other languages can benefit from parts: Extract config/base plugin valid for any language/type from Golang #2015
• Add additional features as plugins instead of making the base plugin more and more complex:
  • Finalizers: Feature Request: Finalizer handler scaffolded by default for go/v3 #2010
  • Component config: ⚠ (go/v3-alpha) Adding support for scaffolding with a versioned ComponentConfig #1790
  • Declarative pattern: currently implemented through an experimental outdated plugin system prior to phase 1.

This updated design has been validated with operator-SDK: operator-framework/operator-sdk/pull/4581

[Adirio]

@camilamacedo86 @DirectXMan12 @estroz @jmrodri @joelanford

[camilamacedo86]

User Stories

• As operator developer would like to generate a project with custom plugins that will be used by default so that, after generating a project with a custom plugin such as kb init—plugins=go/v3,declarative all APIs scaffolded with kb create api subcommand all APIs scaffold will be customized with the optional plugin declarative.

• As an operator developer would like to use a custom plugin just for a specific subcommand so that, I can, for example, use the declarative pattern only for a specific API and not for all project (e.g kb create api subcommand all APIs scaffold will be customized with the optional plugin declarative). More info; Allow every command to overwrite project-configured plugins #1941

• As a KB maintainer/contributor and/or consumer I would like to know the plugins used to configure a project as its specific configurations and data when required so that, I can tooling upgrade and modifications actions to help the users implement smarter plugins. More info; Allow every command to overwrite project-configured plugins #1941

• As a KB maintainer/contributor and/or consumer I would like to define a plugin is composed of 2 or more plugins so that, I can create a plugin that will re-use the code of other plugins and has customizations on top to address my need such as go/v3 + helm/v3 + plugin that does all required adjustments that make my hybrid operator works and to be able to extract the default configuration from the language files and provide different options for configuration without increase the maintainability and bring facilities to ensure the backwards compatibilities of the plugin. Also, I can easily imply that for example that any go/v3 plugin scaffold by my CLI also will be customized with my specific requirements which is a current SDK requirement.

[camilamacedo86]

The changes proposed here are implemented in the PRs #2060 and operator-framework/operator-sdk#4581 already.

IMO it is very important because It allows the KB api starts to provide the required flexibilities for its consumer's plugin as SDK to be easier maintained as it shows a pre-requirement to start to promote solutions where people would write their own plugins to be integrated/useful for the tools.

In this way, I believe that is the first step for we have a design that allows us to start to play with.

Also, added some suggestions/ideas for clarifications such as by adding use cases and goals or non-goals of this proposal. Feel free to check and address them as, please you.

Otherwise, I have no objections and it shows great for me. 🥇

[estroz]

/lgtm

[k8s-ci-robot]

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This pull-request has been approved by: Adirio, camilamacedo86, estroz

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[estroz]

@DirectXMan12 has a review incoming.

/hold

[estroz]

Nevermind, I think #2060 was the subject of discussion, not this PR.

/hold cancel