Enabling ExpandPersistentVolumes - kubernetes

Question

I need to resize a bunch of PVCs. It seems the easiest way to do it is through
the ExpandPersistentVolumes feature. I am however having trouble getting the
configuration to cooperate.
The ExpandPersistentVolumes feature gate is set in kubelet on all three
masters, as shown:
(output trimmed to relevant bits for sanity)
$ parallel-ssh -h /tmp/masters -P "ps aux | grep feature"
172.20.53.249: root 15206 7.4 0.5 619888 83952 ? Ssl 19:52 0:02 /opt/kubernetes/bin/kubelet --feature-gates=ExpandPersistentVolumes=true,ExperimentalCriticalPodAnnotation=true
[1] 12:53:08 [SUCCESS] 172.20...
172.20.58.111: root 17798 4.5 0.5 636280 87328 ? Ssl 19:51 0:04 /opt/kubernetes/bin/kubelet --feature-gates=ExpandPersistentVolumes=true,ExperimentalCriticalPodAnnotation=true
[2] 12:53:08 [SUCCESS] 172.20...
172.20.53.240: root 9287 4.0 0.5 645276 90528 ? Ssl 19:50 0:06 /opt/kubernetes/bin/kubelet --feature-gates=ExpandPersistentVolumes=true,ExperimentalCriticalPodAnnotation=true
[3] 12:53:08 [SUCCESS] 172.20..
The apiserver has the PersistentVolumeClaimResize admission controller, as shown:
$ kubectl --namespace=kube-system get pod -o yaml | grep -i admission
/usr/local/bin/kube-apiserver --admission-control=Initializers,NamespaceLifecycle,LimitRanger,ServiceAccount,PersistentVolumeLabel,DefaultStorageClass,DefaultTolerationSeconds,MutatingAdmissionWebhook,ValidatingAdmissionWebhook,NodeRestriction,PersistentVolumeClaimResize,ResourceQuota
/usr/local/bin/kube-apiserver --admission-control=Initializers,NamespaceLifecycle,LimitRanger,ServiceAccount,PersistentVolumeLabel,DefaultStorageClass,DefaultTolerationSeconds,MutatingAdmissionWebhook,ValidatingAdmissionWebhook,NodeRestriction,PersistentVolumeClaimResize,ResourceQuota
/usr/local/bin/kube-apiserver --admission-control=Initializers,NamespaceLifecycle,LimitRanger,ServiceAccount,PersistentVolumeLabel,DefaultStorageClass,DefaultTolerationSeconds,MutatingAdmissionWebhook,ValidatingAdmissionWebhook,NodeRestriction,PersistentVolumeClaimResize,ResourceQuota
However, when I create or edit a storage class to add allowVolumeExpansion,
it is removed on save. For example:
$ cat new-sc.yaml
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
creationTimestamp: null
labels:
k8s-addon: storage-aws.addons.k8s.io
name: gp2-2
selfLink: /apis/storage.k8s.io/v1/storageclasses/gp2
parameters:
encrypted: "true"
kmsKeyId: arn:aws:kms:us-west-2:<omitted>
type: gp2
zone: us-west-2a
provisioner: kubernetes.io/aws-ebs
reclaimPolicy: Delete
allowVolumeExpansion: true
$ kubectl create -f new-sc.yaml
storageclass "gp2-2" created
$ kubectl get sc gp2-2 -o yaml
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
creationTimestamp: 2018-05-22T20:00:17Z
labels:
k8s-addon: storage-aws.addons.k8s.io
name: gp2-2
resourceVersion: "2546166"
selfLink: /apis/storage.k8s.io/v1/storageclasses/gp2-2
uid: <omitted>
parameters:
encrypted: "true"
kmsKeyId: arn:aws:kms:us-west-2:<omitted>
type: gp2
zone: us-west-2a
provisioner: kubernetes.io/aws-ebs
reclaimPolicy: Delete
What am I missing? What is erasing this key from my storageclass configuration?
EDIT: Here is the command used by the kube-apiserver pods. It does not say anything about feature gates. The cluster was launched using Kops.
- /bin/sh
- -c
- mkfifo /tmp/pipe; (tee -a /var/log/kube-apiserver.log < /tmp/pipe & ) ; exec
/usr/local/bin/kube-apiserver --address=127.0.0.1 --admission-control=Initializers,NamespaceLifecycle,LimitRanger,ServiceAccount,PersistentVolumeLabel,DefaultStorageClass,DefaultTolerationSeconds,MutatingAdmissionWebhook,ValidatingAdmissionWebhook,NodeRestriction,PersistentVolumeClaimResize,ResourceQuota
--allow-privileged=true --anonymous-auth=false --apiserver-count=3 --authorization-mode=RBAC
--basic-auth-file=/srv/kubernetes/basic_auth.csv --client-ca-file=/srv/kubernetes/ca.crt
--cloud-provider=aws --etcd-cafile=/srv/kubernetes/ca.crt --etcd-certfile=/srv/kubernetes/etcd-client.pem
--etcd-keyfile=/srv/kubernetes/etcd-client-key.pem --etcd-servers-overrides=/events#https://127.0.0.1:4002
--etcd-servers=https://127.0.0.1:4001 --insecure-port=8080 --kubelet-preferred-address-types=InternalIP,Hostname,ExternalIP
--proxy-client-cert-file=/srv/kubernetes/apiserver-aggregator.cert --proxy-client-key-file=/srv/kubernetes/apiserver-aggregator.key
--requestheader-allowed-names=aggregator --requestheader-client-ca-file=/srv/kubernetes/apiserver-aggregator-ca.cert
--requestheader-extra-headers-prefix=X-Remote-Extra- --requestheader-group-headers=X-Remote-Group
--requestheader-username-headers=X-Remote-User --secure-port=443 --service-cluster-ip-range=100.64.0.0/13
--storage-backend=etcd3 --tls-cert-file=/srv/kubernetes/server.cert --tls-private-key-file=/srv/kubernetes/server.key
--token-auth-file=/srv/kubernetes/known_tokens.csv --v=1 > /tmp/pipe 2>&1

Answer 1

It could happen if you did not enable alpha feature-gate for the option.
Did you set --feature-gates option for kube-apiserver?
--feature-gates mapStringBool - A set of key=value pairs that describe feature gates for alpha/experimental features. Options are:
...
ExpandPersistentVolumes=true|false (ALPHA - default=false)
...
Update: If you don't see this option in the command line arguments, you need to add it (--feature-gates=ExpandPersistentVolumes=true).
In case you run kube-apiserver as a pod, you should edit /etc/kubernetes/manifests/kube-apiserver.yaml and add the feature-gate option to other arguments. kube-apiserver will restart automatically.
In case you run kube-apiserver as a process maintained by systemd, you should edit kube-apiserver.service or service options $KUBE_API_ARGS in a separate file, and append feature-gate option there. Restart the service with systemctl restart kube-apiserver.service command.
After enabling it, you can create a StorageClass object with allowVolumeExpansion option:
# kubectl get sc -o yaml --export
apiVersion: v1
items:
- allowVolumeExpansion: true
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
creationTimestamp: 2018-05-23T14:38:43Z
labels:
k8s-addon: storage-aws.addons.k8s.io
name: gp2-2
namespace: ""
resourceVersion: "1385"
selfLink: /apis/storage.k8s.io/v1/storageclasses/gp2-2
uid: fe516dcf-5e96-11e8-a86d-42010a9a0002
parameters:
encrypted: "true"
kmsKeyId: arn:aws:kms:us-west-2:<omitted>
type: gp2
zone: us-west-2a
provisioner: kubernetes.io/aws-ebs
reclaimPolicy: Delete
volumeBindingMode: Immediate
kind: List
metadata:
resourceVersion: ""
selfLink: ""