Formalize and define schema for devfile registry index (index.json)

[johnmcollier]

Currently, devfile registries host an index.json file that contains the registry index and the devfiles it contains, partially built from each devfile's meta.yaml.

[
  {
    "name": "java-maven",
    "displayName": "Maven Java",
    "description": "Upstream Maven and OpenJDK 11",
    "tags": [
      "Java",
      "Maven"
    ],
    "projectType": "maven",
    "language": "java",
    "links": {
      "self": "/devfiles/java-maven/devfile.yaml"
    }
  }
]

Devfile consumers such as Odo or Che then parse this file when looking for devfiles in a given registry.

However the schema for the index.json file is not formally defined anywhere, nor is there a list of which fields are required vs. optional. Additionally, Che and Odo both use different generators to create the index.json (see Che and Odo).

We should formally define the schema for the index.json file, as well as capture any changes to the schema discussed on here in the past few months. This will ensure consistency across the board for devfile registries and devfile consumers.

List of agreed-upon index.json changes:

• Devfile name: v2 devfile registry's index should have a stack name info #78
• StarterProjects: Devfile registry index should contain the starterProjects for each devfile #115

Other agreed-upon devfile metadata changes that may be relevant:

• Matching Rules: Stacks/Devfile matching rules #40
• Website: Devfile metadata: add a link to an external website #38

Registry index file generator:
This item also includes the implementation of the registry index file (index.json) generator that is used for generating the registry index file for storing the catalog and metadata of stacks/devfiles in the registry.

[johnmcollier]

Some other things to consider:

1. How/if moving to OCI registries will impact the index.json (and how the index.json is built)
2. Moving to one, consistent generator to build the index.json file

[GeekArthur]

Probably we need to open a separate issue for registry index file generator, but given the design of OCI registry is not finalized, not sure how we would like to proceed it as the generator may change with the registry migrates to OCI-based registry.

[GeekArthur]

Based on the discussion, we decide to still use our own index file instead of OCI index file. Given there is no strong relation between index file and devfile artifact manifest file, so I think we can still use each devfile's meta.yaml to generate the index file.

[GeekArthur]

The index generator POC has been pushed to https://github.com/devfile/registry-support/tree/index-generator. One thing we need to discuss on Cabal call is whether we need to merge meta.yaml and devfile.yaml or not.

[GeekArthur]

Issue is open for discussion regarding merge meta.yaml and devfile.yaml: #172

[GeekArthur]

Last sub-issue #172 is done, close this issue.