Evaluate the existing ocm controller oci cache implementation

[fabianburth]

Evaluate the existing ocm controllers oci cache / storage backend implementation (the implementation also includes code for setting up single layer oci artifacts).
Quickly document your evaluation and deduct further steps for this epic (it's absolute fine if that involves a lot of copy pasting!) and follow up tasks such as #75 .

• Decide on Artifact Type (ADR type option 2 vs. option 5)
• Decide on OCI Registry (ADR OCI Registry options)

[frewilhelm]

Notes:

• Snapshot (Based on README.md)
  • Kubernetes custom resource that manages a Flux compatible single-layer OCI image to enable interoperability between OCM and Flux
  • Created by controller (never manually)
  • CRD contains
    • Spec:
      • digest
      • identity (ocm based?)
      • tag (where comes this from?)
    • Status:
      • digest (again?)
      • repositoryURL (url to registry with path to sha (sha differs from digest above. however, both have sha256 prefix))
      • tag (again?)
• snapshots are immutable, Flux-compatible, single layer OCI images containing a single OCM resource. Snapshots are stored in an in-cluster registry and in addition to making component resources accessible for transformation, they also can be used as a caching mechanism to reduce unnecessary calls to the source OCM registry. (source)

Result: In comparison to the artifact in v2, this snapshot seems a bit loaded. The information in spec and status are redundant and the fields identity and tag are not explained (at least not in the README.md or in its definition in api/v1alpha1/snapshot_types.go)

• Registry
  • HTTPS OCI registry is created in this project (how?)
  • Is a "sync-point" between ocm-controller and Flux eco-system and serves as cache.
    • What is meant with "sync-point"?
  • Is used by Resource, Localization, and Configuration as cache (exclusively?)
  • A remote resource is only fetched once and is then provided by the local registry.
  • Where and how is the registry deployed?

[ikhandamirov]

Registry

HTTPS OCI registry is created in this project (how?)
Where and how is the registry deployed?

Part of the controller's helm chart: https://github.com/open-component-model/ocm-controller/blob/main/deploy/templates/deployment_registry.yaml#L21
There is no tight coupling between controllers and the registry, just the registry URL as the interface:

• https://github.com/open-component-model/ocm-controller/blob/main/deploy/templates/deployment_manager.yaml#L31
• https://github.com/open-component-model/ocm-controller/blob/main/deploy/values.yaml#L4

[frewilhelm]

The evaluation for the snapshot resource is finished as we discussed in #92.

[frewilhelm]

I propse to close the issue as the initial evaluation happened and everything else is discussed in #92