When upgrading to a new LWS version, rolling update gets triggered

[Edwinhr716]

What happened:
When updating from release-0.2.0 to release-0.4.2, the template hash label in the pods and statefulsets changes, despite the LWS object not changing. This triggers a rolling update, even though it shouldn't.

What you expected to happen:
Update to happen without triggering rolling updates

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

1. Deploy the lws controller with version 0.2
2. Deploy a yaml with a volumeMount

apiVersion: leaderworkerset.x-k8s.io/v1
kind: LeaderWorkerSet
metadata:
  labels:
    app.kubernetes.io/name: leaderworkerset
    app.kubernetes.io/instance: leaderworkerset-multi-template
    app.kubernetes.io/part-of: lws
    app.kubernetes.io/managed-by: kustomize
    app.kubernetes.io/created-by: lws
  name: cube
spec:
  replicas: 2
  leaderWorkerTemplate:
    size: 4
    workerTemplate:
      spec:
        containers:
        - name: nginx
          image: nginx:1.14.1
          resources:
            limits:
              cpu: "100m"
            requests:
              cpu: "50m"
          ports:
          - containerPort: 8080
          volumeMounts:
          - name: dshm
            mountPath: /dev/shm
        volumes:
        - name: dshm
          emptyDir:
            medium: Memory

3. Upgrade the lws controller to 0.4.2

Anything else we need to know?:
The template hash is generated using the string version of the two pod templates. When new fields are added to other Kubernetes objects that can be part of the pod template spec, that will change the underlying string, even the new fields are not set.

You can see this when comparing the podTemplateSpec used to generate the template hash in version 0.2 versus the one used on version 0.4.2

Version to 0.2

[] Volume {
    Volume {
        Name: dshm,
        VolumeSource: VolumeSource {
            HostPath: nil,
            EmptyDir: & EmptyDirVolumeSource {
                Medium: Memory,
                SizeLimit: < nil > ,
            },
            GCEPersistentDisk: nil,
            AWSElasticBlockStore: nil,
            GitRepo: nil,
            Secret: nil,
            NFS: nil,
            ISCSI: nil,
            Glusterfs: nil,
            PersistentVolumeClaim: nil,
            RBD: nil,
            FlexVolume: nil,
            Cinder: nil,
            CephFS: nil,
            Flocker: nil,
            DownwardAPI: nil,
            FC: nil,
            AzureFile: nil,
            ConfigMap: nil,
            VsphereVolume: nil,
            Quobyte: nil,
            AzureDisk: nil,
            PhotonPersistentDisk: nil,
            PortworxVolume: nil,
            ScaleIO: nil,
            Projected: nil,
            StorageOS: nil,
            CSI: nil,
            Ephemeral: nil,
        },
    },
}

Version 0.4.2

[] Volume {
    Volume {
        Name: dshm,
        VolumeSource: VolumeSource {
            HostPath: nil,
            EmptyDir: & EmptyDirVolumeSource {
                Medium: Memory,
                SizeLimit: < nil > ,
            },
            GCEPersistentDisk: nil,
            AWSElasticBlockStore: nil,
            GitRepo: nil,
            Secret: nil,
            NFS: nil,
            ISCSI: nil,
            Glusterfs: nil,
            PersistentVolumeClaim: nil,
            RBD: nil,
            FlexVolume: nil,
            Cinder: nil,
            CephFS: nil,
            Flocker: nil,
            DownwardAPI: nil,
            FC: nil,
            AzureFile: nil,
            ConfigMap: nil,
            VsphereVolume: nil,
            Quobyte: nil,
            AzureDisk: nil,
            PhotonPersistentDisk: nil,
            PortworxVolume: nil,
            ScaleIO: nil,
            Projected: nil,
            StorageOS: nil,
            CSI: nil,
            Ephemeral: nil,
            Image: nil,
        },
    },
}

The latter contains the field Image: nil, which was added in v0.31.0 of k8s.io/apimachinery https://pkg.go.dev/k8s.io/api/core/v1#ImageVolumeSource. 0.2 uses version v0.29.3, while 0.4.2 uses version v.0.31.0

Environment:

• Kubernetes version (use kubectl version):
• LWS version (use git describe --tags --dirty --always):
• Cloud provider or hardware configuration:
• OS (e.g: cat /etc/os-release):
• Kernel (e.g. uname -a):
• Install tools:
• Others:

[Edwinhr716]

/assign @Edwinhr716

[ahg-g]

The fix is to use controller revision to track and detect changes to the spec #239