[backstage] Reflect Flux resources into BS entities

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As outlined here: https://github.com/weaveworks/weave-technical-scratchpad/blob/main/kevin/backstage/backstage_gitrepository_resources_as_entities.md

User story:

• As a User I use backstage a lot and use its dependency declaration system to do things like declaring that team-salsa owns a particular git-repo, so I can contact them if I have questions, need to change something etc.

Question:

• Would this go in EE or OSS BS plugin? Probably OSS

Behaviour:

• When I add a Flux GitRepository (or hr,ks,helmrepo etc) to my cluster, I see a BS "Kind: Resource" entity appear in the BS catalog
• This allows me to declare relationships between different flux resources AND other BS entities like Users / services / etc.
• E.g. we could reference a flux bs resource like this: https://github.com/weaveworks/backstage-sockshop/blob/main/components/catalogue-service.yaml#L21-L22

Tasks

• run the command to generate new backstage backend plugin https://backstage.io/docs/plugins/backend-plugin, yarn new --select backend-plugin maybe called catalog-backend-module-flux
• Wanna install it very similarly to other entityprovider plugins

import { FluxEntityProvider } from '@backstage/plugin-catalog-backend-module-flux';

...

builder.addEntityProvider(
  FluxEntityProvider.fromConfig({
    logger: env.logger,
    scheduler: env.scheduler,
    config: env.config
  })
);

And add some more config stuff:

catalog:
  providers:
    flux:
      gitrepositories:
        labelSelector:
          example.com/git: true
        schedule:
          frequency: { minutes: 30 }
          timeout: { minutes: 3 }

• And add a schema like this one https://github.com/backstage/backstage/blob/master/plugins/catalog-backend-module-gcp/config.d.ts
• Implement an EntityProvider like https://github.com/backstage/backstage/blob/master/plugins/catalog-backend-module-gcp/src/providers/GkeEntityProvider.ts#L41

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https://github.com/bigkevmcd/backstage-plugins/tree/main/plugins/catalog-backend-module-capi

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https://github.com/AntoineDao/backstage-provider-kubernetes

• What is this existing plugin missing?
• Can we extend this plugin?

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Can we add some other kind of component that will tie into the above plugin? e.g. a

• "processor"?
• "stitcher"?

As seen here https://backstage.io/docs/features/software-catalog/life-of-an-entity/

Or follow the "transformer" pattern, an example of it here: https://github.com/RoadieHQ/roadie-backstage-plugins/tree/main/plugins/backend/catalog-backend-module-okta, e.g that would transform the provided entity here https://github.com/AntoineDao/backstage-provider-kubernetes/blob/main/src/providers/KubernetesProvider.ts#L153

Moving forward:

• Open an issue on the k8s-provider plugin to see if they are interested in doing labeling stuff / transformer stuff?

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Does static ownerShip declarations here: https://github.com/AntoineDao/backstage-provider-kubernetes/blob/main/src/providers/KubernetesProvider.ts#L173C53-L173C53

We want them to be dynamic, based on k8s annotations/labels etc.