Show subscriptions to event types in Backstage

[aliok]

Changes

(see release note below for more details)

Backend:

• Return the Backstage ids of the subscribers of the event types in the Knative Eventing plugin.

Plugin:

• Show subscriptions to event types in Backstage

• Entity providers cannot create the ApiConsumedBy relationship from the API entity side. Created a processor for that reason.

• Diagram: https://gist.github.com/aliok/45d80cb82822142dd6a978c9cc44e12e

Fixes #20

Release Note

Knative event mesh plugin will now show the subscribers of the event types.

It will show this relation if the subscriber is already registered in the Backstage catalog.

Limitations:
- Only the subscriptions via Brokers and Triggers are supported.
- Finding consumers via CloudEvents SQL is not supported yet. See https://github.com/knative-extensions/backstage-plugins/issues/26.
- Relation will only show if the component registered can be matched using the [`backstage.io/kubernetes-id ` label](https://backstage.io/docs/features/kubernetes/configuration#common-backstageiokubernetes-id-label). 
- Finding consumers via [label selectors](https://backstage.io/docs/features/kubernetes/configuration#label-selector-query-annotation) is not supported yet. See https://github.com/knative-extensions/backstage-plugins/issues/30.
- [`backstage.io/kubernetes-namespace` annotation](https://backstage.io/docs/features/kubernetes/configuration#common-backstageiokubernetes-id-label) is currently ignored. See https://github.com/knative-extensions/backstage-plugins/issues/29.
- When trying to match the consumers of eventTypes on Backstage side, pagination is not handled yet. See https://github.com/knative-extensions/backstage-plugins/issues/28.

[knative-prow[bot]]

@aliok: The label(s) kind/<kind> cannot be applied, because the repository doesn't have them.

In response to [this](https://github.com/knative-extensions/backstage-plugins/pull/24): > > > > ># Changes > > > >- Show subscriptions to event types in Backstage (see release note below for more) >- Diagram: https://gist.github.com/aliok/45d80cb82822142dd6a978c9cc44e12e >- WIP PR created for early feedback: > - My efforts to use the subscriber information in the Backstage plugin failed as entity providers cannot create the `ApiConsumedBy` relationship from the API entity side. It needs to be set on the `Component` entity side. This entity cannot be reached in a provider. > - There are missing tests for the backend. Similarly, there are some linting issues. > > >/kind > > >Fixes # > > > >**Release Note** > > >```release-note >Knative event mesh plugin will now show the subscribers of the event types. > >It will show this relation if the subscriber is already registered in the Backstage catalog. >Only the subscriptions via Brokers and Triggers are supported. CloudEvents SQL is not supported yet. >``` > >**Docs** > > >```docs > >``` > Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes/test-infra](https://github.com/kubernetes/test-infra/issues/new?title=Prow%20issue:) repository.

[pierDipi]

There are linting errors

[pierDipi]

LGTM

[aliok]

Screenshots for this setup:

• 3 event types: paymentreceived, paymentprocessed, frauddetected
• 3 consumers: payment-processor, fraud-detector, fraud-logger (these process the events above in the order they're written)
• 1 additional consumer that consumes all events (Trigger w/o filter): all-events-logger
• 1 event generator: payment-event-generator-source (relation not shown in Backstage as we don't show the event sources as a relation)

Components

Already registered on Backstage:

apiVersion: backstage.io/v1alpha1
kind: Component
metadata:
  name: payment-processor
  annotations:
    backstage.io/kubernetes-id: payment-processor
spec:
  lifecycle: production
  owner: guests
  type: service
---
apiVersion: backstage.io/v1alpha1
kind: Component
metadata:
  name: payment-event-generator-source
  annotations:
    backstage.io/kubernetes-id: payment-event-generator-source
spec:
  lifecycle: production
  owner: guests
  type: service
---
apiVersion: backstage.io/v1alpha1
kind: Component
metadata:
  name: fraud-detector
  annotations:
    backstage.io/kubernetes-id: fraud-detector
spec:
  lifecycle: production
  owner: guests
  type: service
---
apiVersion: backstage.io/v1alpha1
kind: Component
metadata:
  name: fraud-logger
  annotations:
    backstage.io/kubernetes-id: fraud-logger
spec:
  lifecycle: production
  owner: guests
  type: service
---
apiVersion: backstage.io/v1alpha1
kind: Component
metadata:
  name: all-events-logger
  annotations:
    backstage.io/kubernetes-id: all-events-logger
spec:
  lifecycle: production
  owner: guests
  type: service

Event types

Event type detail view

all-events-logger component graph

[knative-prow[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aliok, pierDipi

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