fix: don't merge volume mount on sidecar container if it exists

[bnadim]

What and why?

Adding the same volume mounts to sidecar container and to all containers would end up in an error telling that the volume mounts already exist.

Testing Steps

Using this configuration map we would end up getting the error

---
apiVersion: v1
kind: ConfigMap
metadata:
  name: sidecar-injector-gcsfuse
  namespace: kube-system
  labels:
    app: k8s-sidecar-injector
data:
  gcsfuse: |
    name: gcsfuse
    containers:
    - name: gcsfuse
      image: eu.gcr.io/somerepo/gcsfuse:latest
      imagePullPolicy: IfNotPresent
      securityContext:
        privileged: true
        capabilities:
          add: ["SYS_ADMIN"]
      lifecycle:
        postStart:
          exec:
            command: ["gcsfuse", "-o", "nonempty", "some_bucket", "/home/airflow/gcs/"]
        preStop:
          exec:
            command: ["fusermount", "-zu", "/home/airflow/gcs/"]
      volumeMounts:
      - name: gcsdata
        mountPath: /home/airflow/gcs/
        mountPropagation: Bidirectional
    volumes:
      - name: gcsdata
        emptyDir: {}
    volumeMounts:
      - name: gcsdata
        mountPath: /home/airflow/gcs/
        mountPropagation: HostToContainer

Reviewers

Required reviewers: @byxorna
Request reviews from other people you want to review this PR in the "Reviewers" section on the right.

⚠️ this PR must have at least 2 thumbs from the MAINTAINERS.md of the project before merging!

[yahoocla]

Thank you for submitting this pull request, however I do not see a valid CLA on file for you. Before we can merge this request please visit https://yahoocla.herokuapp.com/ and agree to the terms. Thanks! 😄

[bnadim]

i agreed with cla/licenses

[byxorna]

@bnadim thanks for the PR! If you click through that link (https://yahoocla.herokuapp.com/), the CLA bot should update this PR with your acceptance. Great catch on this :)

[byxorna]

Awesome catch! Would you mind adding a test case that illustrates this behavior? (i.e. a pod with a VolumeMount "foo" does not have its volume replaced by a sidecar injector volumemount config "foo")

[byxorna]

cc @iwilltry42 FYI

[iwilltry42]

Thanks for the PR @bnadim , I actually saw this happening as well (only that for me, the pods wouldn't even be launched, so I couldn't see any error messages). Looks like a stupid autocomplete mistake from my side. Now I can scratch this from my TODO-List, thank you :)

@byxorna , thanks for pinging me 👍

[iwilltry42]

Looks like VSCode's autocomplete failed me there, thanks for catching that error 👍

[byxorna]

Hey @bnadim, mind clicking through the linked cla/licenses check and signing the CLA? I would love to merge this change :)

[bnadim]

Hey @bnadim, mind clicking through the linked cla/licenses check and signing the CLA? I would love to merge this change :)

It should be working now

[byxorna]

@bnadim thank you! merging :)