📖 Refactor sampleexternalplugin to be a Valid Reference Implementation

[nerdeveloper]

Summary

This PR refactors the sampleexternalplugin from outdated mock scaffolding into a realistic, working reference implementation that demonstrates best practices for external plugin development.

Problem

The current sampleexternalplugin (issue #4824) had several issues:

• ❌ Mock scaffolding that created useless text files (initFile.txt, apiFile.txt)
• ❌ Didn't use PROJECT config or align with internal plugin architecture
• ❌ Used release module instead of local source for testing
• ❌ Not a realistic example for plugin developers

Solution

Transformed the plugin into a Prometheus Monitoring Generator that:

• ✅ Uses edit subcommand to add optional Prometheus monitoring features
• ✅ Reads PROJECT config for domain and project metadata
• ✅ Generates real ServiceMonitor YAML manifests
• ✅ Uses local Kubebuilder source via replace directive
• ✅ Follows internal plugin architecture patterns

Changes

Plugin Functionality

• Removed: Mock init, create api, create webhook subcommands
• Added: Realistic edit subcommand that scaffolds Prometheus monitoring
• Implements: PROJECT config reading (domain, projectName, repo)
• Generates:
  • config/prometheus/monitor.yaml - ServiceMonitor resource
  • config/prometheus/kustomization.yaml - Kustomize config
  • config/default/kustomization_prometheus_patch.yaml - Integration instructions

Code Quality

• Uses config.Config APIs like internal plugins
• Proper Universe pattern for file scaffolding
• Local source replace directive: replace sigs.k8s.io/kubebuilder/v4 => ../../../../../../../

Documentation

• Updated external-plugins.md with realistic edit command examples
• Changed examples from mock init/api/webhook to real Prometheus monitoring use case

Usage Example

# Add Prometheus monitoring to your operator project
kubebuilder edit --plugins sampleexternalplugin/v1

This will scaffold:

• Prometheus ServiceMonitor configuration
• Kustomize resources for monitoring
• Integration instructions

Testing

• ✅ Plugin builds successfully with local source
• ✅ All mock files removed, real templates in place
• ✅ Documentation reflects new usage

Impact

This PR makes the sample plugin a proper reference that:

• Shows how to read PROJECT config in external plugins
• Demonstrates real-world use case (optional monitoring features)
• Allows contributors to test against local Kubebuilder source
• Aligns with internal plugin architecture patterns

Fixes #4824

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[k8s-ci-robot]

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[vitorfloriano]

Hi @nerdeveloper thanks for the PR! This is a large one and will take some time to review. While you wait for the review, could you please adjust the title so it follows the guidelines for PR titles? Also, could you squash the four commits into one just so we keep the rule of a single commit per PR? Thanks!

[camilamacedo86]

Thank you for your contribution 🥇
I tried give the first round of reviews, let me know wdyt.

[Copilot]

Pull Request Overview

This PR refactors the sampleexternalplugin from mock scaffolding into a realistic Prometheus monitoring generator that demonstrates best practices for external plugin development. The plugin now uses the edit subcommand to add optional monitoring features by reading PROJECT config and generating actual ServiceMonitor YAML manifests.

Key Changes:

• Removed mock init, create api, and create webhook subcommands in favor of realistic edit subcommand
• Implemented PROJECT config reading using config.Config APIs similar to internal plugins
• Added local source replace directive for testing against local Kubebuilder source

Reviewed Changes

Copilot reviewed 20 out of 21 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
v1/scaffolds/init.go	Updated to scaffold Prometheus monitoring resources during initialization
v1/scaffolds/edit.go	New file implementing edit subcommand with PROJECT config loading
v1/scaffolds/api.go	Removed - mock create api subcommand deleted
v1/scaffolds/webhook.go	Removed - mock create webhook subcommand deleted
v1/internal/test/plugins/prometheus/prometheus.go	New Prometheus instance manifest template
v1/internal/test/plugins/prometheus/kustomization.go	New kustomization templates for Prometheus resources
v1/cmd/cmd.go	Updated command routing to support init and edit only
v1/cmd/metadata.go	Updated to handle init and edit metadata requests
v1/cmd/flags.go	Refactored flag handling for init and edit subcommands
v1/go.mod	Added afero dependency and local source replace directive
v1/test/test.sh	Updated test to verify Prometheus asset scaffolding
external-plugins.md	Updated documentation with realistic edit command examples
v1/testdata/testplugin/*	Removed mock test files
v1/scaffolds/internal/templates/*	Removed mock template files

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[Copilot]

The test checks for prometheus.yaml but the code scaffolds the file at path config/prometheus/prometheus.yaml according to prometheus.go line 47. The filename should be prometheus.yaml, not monitor.yaml as mentioned in the PR description.

[Copilot]

Converting len(pr.Args) to a rune and then to a string produces a Unicode character, not a numeric string. This will result in confusing error messages. Use strconv.Itoa(len(pr.Args)) or fmt.Sprintf(\"%d\", len(pr.Args)) instead.

[Copilot]

Silently returning default values when the PROJECT file doesn't exist could mask configuration issues. For the edit subcommand, which expects to modify an existing project, consider returning an error instead to inform users that they need to run init first.

Suggested change

	return &ProjectConfig{
	Domain: "example.com",
	ProjectName: "project",
	Repo: "example.com/project",
	}, nil
	return nil, fmt.Errorf("PROJECT file does not exist; please run 'init' first")