kubectl kustomize v. 1.21 not supporting YAML references

[ZhilinS]

What happened:
After upgrading kubectl to version 1.21 kustomize command fails when YAML anchors are references by '<<'

What you expected to happen:
As it was in v. 1.20, command should provide correct output, but not the erorr

How to reproduce it (as minimally and precisely as possible):
Given this 2 files:

kustomization.yaml
api.yaml

kustomization.yaml:

---
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

resources:
  - api.yaml

api.yaml:

apiVersion: v1
kind: Service
metadata:
  name: service
  labels: &labels
    label: test
spec:
  selector:
    <<: *labels

Execute kubectl kustomize . and see the following output:
v. 1.20:

apiVersion: v1
kind: Service
metadata:
  labels:
    label: test
  name: service
spec:
  selector:
    label: test

v. 1.21:

Error: map[string]interface {}{"apiVersion":"v1", "kind":"Service", "metadata":map[string]interface {}{"labels":map[string]interface {}{"label":"test"}, "name":"service"}, "spec":map[string]interface {}{"selector":map[interface {}]interface {}{"label":"test"}}}: json: unsupported type: map[interface {}]interface {}

So, now kubectl cannot recognize << while parsing yaml. Replacement with any string fixes the issue. Even "<<" fixes it.

Environment:

• Server version doesn't matter, 'cause it's happening on a client command step

[k8s-ci-robot]

@ZhilinS: This issue is currently awaiting triage.

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[ZhilinS]

It can be fixed by changing api.yaml to

apiVersion: v1
kind: Service
metadata:
  name: service
  labels: &labels
    label: test
spec:
  selector: *labels

but it's strange to see that previous version of tool was working with standard YAML syntax and the newest one isn't

[sameersbn]

We have been experiencing a lot of issues with regard to the use of anchors. Following YAML that used to work with kubectl v1.20.4 no longer seems to be working and errors out with the message : node must be a scalar, sequence or map.

 apiVersion: rbac.authorization.k8s.io/v1
 kind: ClusterRoleBinding
 metadata:
   name: &app my-app
 subjects:
 - kind: ServiceAccount
   name: *app
 roleRef:
   apiGroup: rbac.authorization.k8s.io
   kind: ClusterRole
   name: *app

Also rendering https://github.com/knative-sandbox/eventing-kafka-broker/releases/download/v0.22.1/eventing-kafka-controller.yaml using kubectl kustomize errors out due to the following usage:

          livenessProbe:
            !!merge <<: *probe
            initialDelaySeconds: 20

Similarly rendering https://github.com/knative-sandbox/eventing-kafka/releases/download/v0.22.3/source.yaml errors out due to the use of YAML anchors.

edit: none of the above issues are experienced with kubectl 1.20.4

[KnVerey]

Kubectl 1.21 contains a large version bump to Kustomize, from v2 to v4. There are already several issues open on the Kustomize repo about problems with YAML anchors. Please follow along there. I believe the most relevant to this particular case is https://github.com/kubernetes-sigs/kustomize/issues/3614.

/triage duplicate
/close

[k8s-ci-robot]

@KnVerey: Closing this issue.

In response to this:

Kubectl 1.21 contains a large version bump to Kustomize, from v2 to v4. There are already several issues open on the Kustomize repo about problems with YAML anchors. Please follow along there. I believe the most relevant to this particular case is https://github.com/kubernetes-sigs/kustomize/issues/3614.

/triage duplicate
/close

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.