[stable/kube-slack] To run kube-slack as non root

[pierluigilenoci]

What this PR does / why we need it:

To run kube-slack as non root

Which issue this PR fixes

No issue to fix, only an improvement

Special notes for your reviewer:

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• DCO signed
• Chart Version bumped
• Variables are documented in the README.md
• Title of the PR starts with chart name (e.g. [stable/mychartname])

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: pierluigilenoci
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[k8s-ci-robot]

Hi @pierluigilenoci. Thanks for your PR.

I'm waiting for a helm member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[jstriebel]

@pierluigilenoci Thanks for your PR. Accoding to the current Dockerfile the container would already be running as non-root. Why exactly would the proposed change be necessary?

If you want to move forward with this PR please merge the newest changes from your previous commit also.

[pierluigilenoci]

@jstriebel according to my knowledge if you use an "alphanumeric" user you get this error from K8s: "container has runAsNonRoot and image has non-numeric user (%s), cannot verify user is non-root". So we need to add a securityContext inside the deployment with a proper runAsUser parameter.
Another viable option, but more complex and, for me, it's not worth it, is to introduce a Pod Security Policy.

[pierluigilenoci]

Recreate the PR here #21983