Validate Resource Graphs

[srohatgi]

Currently, the graph lib synchronizes resource graphs based on a correct dependency order. Following validation is performed:

• dependencies within resources should always resolve correctly

Missing dependencies on a resource graph is not validated. This enhancement proposes adding validation capability for a given graph kind.

Proposed api changes:

// Opts captures customizable functionality like logging
type Opts struct {
  CustomLogger func(args ...interface{})
  Decorator    func(r Resource) Resource

  // Validator captures constrained dependency graph kinds
  Validator    map[string][]Resource
}

// Sync method uses the Resource slice to generate a DAG. The DAG is verified by comparing it to the 
// `kind` parameter. The DAG is processed based on the value of toDelete flag. Resources may be 
// processed concurrently. Processed resources may return a status string and or an error. The function 
// collects these and aggregates them in respective maps keyed by resource names.
func (lib *Lib) Sync(ctxt context.Context, kind string, resources []Resource, toDelete bool) (map[string]string, error)

[srohatgi]

@melugoyal @sanishmahadik @gaurav-chawla please review and comment.

[sanishmahadik]

Why not use the k8s CR validations instead? We can create different CRs for different kind of use-cases and then add this validation on those.

[srohatgi]

@sanishmahadik certainly possible; how are you proposing k8s CR validation will work?

[srohatgi]

@sanishmahadik - the idea I have is to take the template

map[string][]Resource

and generate the openapi-v3 schema spec. IMO, this helps us open the maestro platform for folks to use their own favorite crd generator.

[sanishmahadik]

This is what the structural schema is supposed to do in k8s CRD: https://kubernetes.io/docs/tasks/extend-kubernetes/custom-resources/custom-resource-definitions/#specifying-a-structural-schema