validation webhook did not catch misspelled filter

[szuecs]

Describe the bug

RouteGroup created

spec:
  backends:
  - address: https://app.example.org/
    name: app
    type: network
  defaultBackends:
  - backendName: app
  hosts:
  - my-host.example.org
  routes:
  - filters:
    - bearerInjector("app/app-secret") # <- filter does not exist (camelcase here)
    pathSubtree: /

Expected behavior

This should not be an allowed change

Observed behavior

It was submitted without error

[AlexanderYastrebov]

I guess the proper validation should

1. parse eskip and check there is a single filter (doable)
2. check filter name (seems doable, needs filter registry)
3. check args (seems tricky as it would need to actually create filter which might be impossible (e.g. static filter checks directory permissions) )

somewhere along the

skipper/dataclients/kubernetes/definitions/routegroups.go

Lines 397 to 407 in 807227a

	if hasEmpty(r.Predicates) {
	return errInvalidPredicate
	}
	if hasEmpty(r.Filters) {
	return errInvalidFilter
	}
	if hasEmpty(r.Methods) {
	return errInvalidMethod
	}

The same is for predicates. Maybe 1. and 2. could be a good start.

[AlexanderYastrebov]

Linking the comment #1537 (comment) from @aryszka touching route validation

[AlexanderYastrebov]

Related issue #1333

[MustafaSaber]

I see 2 problems with point 2 in this comment #1618 (comment)

1. We will need to export filter registry somehow from Skipper and will break admission webhook interface and we won't be able to send it to anyway.

   1. https://github.com/zalando/skipper/blob/master/cmd/webhook/main.go#L58 ->
   2. https://github.com/zalando/skipper/blob/master/cmd/webhook/admission/admission.go#L106 ->
   3. https://github.com/zalando/skipper/blob/master/cmd/webhook/admission/admission.go#L72 ->
   4. https://github.com/zalando/skipper/blob/master/cmd/webhook/admission/admission.go#L87 (where validation happens)
      How can we move filterRegistry from i to iv if it's created in skipper?

2. We don't have predicate registry so checking predicate name only also not valid

[MustafaSaber]

We need the routing tree so some ideas:

1. Initiate Skipper/routing inside admission
2. Initiate Admission inside Skipper
3. Initiate Skipper inside RouteSRV