kubectl diff does apply

[Djabx]

What happened:

kubectl diff modify my deployements.

What you expected to happen:

I expect the diff command to not change my deployments !

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

Here is what I've done

1. Create a simple pod test.yaml

apiVersion: v1
kind: Pod
metadata:
  name: myapp-pod
  labels:
    app: myapp
spec:
  containers:
  - name: myapp-container
    image: bash:5.0.11
    command: ['bash', '-c', 'bash --version && sleep 3600']

kubectl apply -f test.yaml

$ kubectl logs myapp-pod
GNU bash, version 5.0.11(1)-release (x86_64-pc-linux-musl)
Copyright (C) 2019 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

2. Modify the pod

apiVersion: v1
kind: Pod
metadata:
  name: myapp-pod
  labels:
    app: myapp
spec:
  containers:
  - name: myapp-container
    image: bash:5.0.16
    command: ['bash', '-c', 'bash --version && sleep 3600']

3. Make a diff: kubectl diff -f test.yaml

iff -u -N /tmp/LIVE-275879232/v1.Pod.default.myapp-pod /tmp/MERGED-622230431/v1.Pod.default.myapp-pod
--- /tmp/LIVE-275879232/v1.Pod.default.myapp-pod	2020-04-02 12:43:39.678749329 +0200
+++ /tmp/MERGED-622230431/v1.Pod.default.myapp-pod	2020-04-02 12:43:39.778748987 +0200
@@ -11,7 +11,7 @@
     app: myapp
   name: myapp-pod
   namespace: default
-  resourceVersion: "10692283"
+  resourceVersion: "10692424"
   selfLink: /api/v1/namespaces/default/pods/myapp-pod
   uid: 6cbb52a5-0adc-40ad-b435-0f41a037c183
 spec:
@@ -20,7 +20,7 @@
     - bash
     - -c
     - bash --version && sleep 3600
-    image: bash:5.0.11
+    image: bash:5.0.16
     imagePullPolicy: IfNotPresent
     name: myapp-container
     resources:

4. See what appends...

$ k describe pod myapp-pod
[...]
Containers:
  myapp-container:
    Container ID:  docker://3e4404eaa46dd07b8157fef0259520ab93e3aaf3b3c3dea47195b115463c89bb
    Image:         bash:5.0.16
    Image ID:      docker-pullable://bash@sha256:febb3d74f41f2405fe21b7c7b47ca1aee0eda0a3ffb5483ebe3423639d30d631
[...]

Anything else we need to know?:

Environment:

• Kubernetes version (use kubectl version): v1.18.0 (commit 9e99141)
• Cloud provider or hardware configuration: gke v1.15.9-gke.26
• OS (e.g: cat /etc/os-release): Alpine Linux v3.11.5
• Kernel (e.g. uname -a): Linux myapp-pod 4.14.138+
• Install tools:
• Network plugin and version (if this is a network-related bug):
• Others:

[Djabx]

/sig cli
/wg apply

[zhouya0]

This is really a bug. I'll try to fix this.
/assign

[captncraig]

I've also hit this with configmaps unexpectedly updating while running diff. On both AKS and GKE kubernetes 1.14 and 1.15. Kubectl 1.18 local.

[captncraig]

This issue is not present in kubectl version 1.17.4. Downgrading my local client made diffs work as expected again.

[zhouya0]

This PR will fix it. #89795 :)

[HaveFun83]

Same here. Thx for the fix