Cannot list custom objects defined by CRD with non-conventional pluralization

[ayj]

Is this a BUG REPORT or FEATURE REQUEST?:

/kind bug

What happened:

kubectl get route-rules.config.istio.io fails and prints "the server doesn't have a resource type "route-rules" in group "config.istio.io" with the following CRD.

apiVersion: apiextensions.k8s.io/v1beta1
kind: CustomResourceDefinition
metadata:
  name: route-rules.config.istio.io
spec:
  group: config.istio.io
  names:
    kind: RouteRule
    plural: route-rules
    singular: routerule
  version: v1alpha2

What you expected to happen:

kubectl get route-rules.config.istio.io should return the list of custom objects defined by the route-rules.config.istio.io CRD or No resources found if no objects have been created yet.

How to reproduce it (as minimally and precisely as possible):

Non-working example

$ cat bad.yaml 
apiVersion: apiextensions.k8s.io/v1beta1
kind: CustomResourceDefinition
metadata:
  name: route-rules.config.istio.io
spec:
  group: config.istio.io
  names:
    kind: RouteRule
    plural: route-rules
    singular: routerule
  version: v1alpha2

$ kubectl apply -f bad.yaml 
customresourcedefinition "route-rules.config.istio.io" created

$ kubectl get route-rules.config.istio.io
the server doesn't have a resource type "route-rules" in group "config.istio.io"

Anything else we need to know?:

The following CRD does work as expected.

apiVersion: apiextensions.k8s.io/v1beta1
kind: CustomResourceDefinition
metadata:
  name: routerules.config.istio.io
spec:
  group: config.istio.io
  names:
    kind: RouteRule
    plural: routerules
    singular: routerule
  version: v1alpha2

$ kubectl get routerules.config.istio.io
No resources found

Environment:

• Kubernetes version (use kubectl version):

Client Version: version.Info{Major:"1", Minor:"7", GitVersion:"v1.7.4", GitCommit:"793658f2d7ca7f064d2bdf606519f9fe1229c381", GitTreeState:"clean", BuildDate:"2017-08-17T08:48:23Z", GoVersion:"go1.8.3", Compiler:"gc", Platform:"linux/amd64"}
Server Version: version.Info{Major:"1", Minor:"7", GitVersion:"v1.7.3", GitCommit:"2c2fe6e8278a5db2d15a013987b53968c743f2a1", GitTreeState:"clean", BuildDate:"2017-08-03T06:43:48Z", GoVersion:"go1.8.3", Compiler:"gc", Platform:"linux/amd64"}

• Cloud provider or hardware configuration: GKE 1.7.3 ALPHA
• OS (e.g. from /etc/os-release):
• Kernel (e.g. uname -a):
• Install tools:
• Others:

[k8s-github-robot]

@ayj
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[ayj]

/cc @lavalamp, @mandarjog, @kyessenov

ref istio/old_pilot_repo#1107

[nikhita]

/sig api-machinery
/area third-party-resource

/cc @sttts @deads2k @enisoc

[lavalamp]

@mbohlool @pwittrock

[alindeman]

I poked at this a bit, and I think it may be more of a CLI UI/UX issue.

While the CLI reports "customresourcedefinition "routerules.config.istio.io" created", kubectl get looks up based on kind (not singular or plural name).

Specifically, if we change kind to something completely arbitrary like Noodle:

apiVersion: apiextensions.k8s.io/v1beta1
kind: CustomResourceDefinition
metadata:
  name: routerules.config.istio.io
spec:
  group: config.istio.io
  names:
    kind: Noodle
    plural: routerules
    singular: routerule
  version: v1alpha2

And apply it:

$ kubectl apply -f noodle.yml
customresourcedefinition "routerules.config.istio.io" created

We get the expected NotFound when listing noodle.config.istio.io or noodles.config.istio.io:

$ kubectl get noodle.config.istio.io
Error from server (NotFound): Unable to list "noodles" ...
$ kubectl get noodles.config.istio.io
Error from server (NotFound): Unable to list "noodles" ...

$ kubectl get routerules.config.istio.io
the server doesn't have a resource type "routerules" in group "config.istio.io"

[sttts]

If anybody wants to work on this, here are some pointers:

• The GET request to the server uses what is called a "resource name" (lower-case, plural, part of the HTTP path, compare https://blog.openshift.com/kubernetes-deep-dive-api-server-part-1/). The resource name for a CRD is the plural name, i.e. the path is /apis/<group>/namespace/default/<plural>.

• kubectl does certain transformations ("REST mappings") from the string given on the command line to the resource name. There are essentially two:

  • shortcut expansion (e.g. kubectl get <CRD-plural> or kubectl get <CRD-short-name>): it uses discovery information to build up the mapping, namely:

    kubernetes/pkg/kubectl/cmd/util/shortcut_restmapper.go

    Line 79 in 8895f31

    func (e shortcutExpander) getShortcutMappings() ([]kubectl.ResourceShortcuts, error) {

    on the kubectl side and

    kubernetes/staging/src/k8s.io/apiextensions-apiserver/pkg/apiserver/customresource_discovery_controller.go

    Line 112 in 33e50da

    apiResourcesForDiscovery = append(apiResourcesForDiscovery, metav1.APIResource{

    on the CRD server side.
  • default mapping using a plural-heuristic (e.g. kubeget get <lower-case-CRD-kind>s.<group>): compare

    kubernetes/staging/src/k8s.io/apimachinery/pkg/api/meta/restmapper.go

    Line 142 in b0b7111

    func UnsafeGuessKindToResource(kind schema.GroupVersionKind) ( /*plural*/ schema.GroupVersionResource /*singular*/, schema.GroupVersionResource) {

    for the apimachinery code, called from kubectl at

    kubernetes/staging/src/k8s.io/client-go/discovery/restmapper.go

    Line 83 in f14618a

    versionMapper.Add(gv.WithKind(resource.Kind), scope)

    .

The problem with the second expansion (of e.g. noodles.config.istio.io) seems to be that it maps noodles.config.istio.io as a GroupKind to the resource name noodles, but /apis/<group>/namespace/default/noodles does not exist.

Maybe @deads2k or @liggitt can confirm or correct my quick observations above.

[deads2k]

Maybe @deads2k or @liggitt can confirm or correct my quick observations above.

It sounds plausible. I'd be happy to see the "let's guess at a plural" code gone.

[ash2k]

Probably caused by #49948.

[mbohlool]

This does not seem to be an api-machinery issue. I will remove sig-api-machinery label and add sig cli.

[liggitt]

it was api-machinery, fixed in #50012