Explain why to use priorityClassName: system-cluster-critical in production

[wallrj]

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I've done some research into the use-cases for setting priorityClassName and what priority class to use. I think cert-manager should use the built in priority class system-cluster-critical, and I've tried to justify that in the document.

It turns out that if you want to use that built in priority class, you (always?) also have to create a ResourceQuota resource, and I've tried to explain that too.

@hawksight interested to know what you think about this new recommendation.

Links:

• https://github.com/cert-manager/cert-manager/pull/1190
• https://github.com/cert-manager/trust-manager/pull/176
• https://github.com/cert-manager/approver-policy/pull/403
• https://github.com/cert-manager/csi-driver/pull/124
• https://github.com/cert-manager/csi-driver-spiffe/pull/20
• https://github.com/jetstack/google-cas-issuer/pull/96
• https://github.com/cert-manager/aws-privateca-issuer/pull/286
• https://linkerd.io/2.15/tasks/customize-install/#add-priorityclass
• https://github.com/kubernetes/design-proposals-archive/blob/main/scheduling/pod-priority-resourcequota.md
• https://github.com/fluxcd/flux2/pull/3802
• https://goteleport.com/docs/reference/helm-reference/teleport-cluster/#priorityclassname
• https://github.com/argoproj/argo-helm/pull/1212

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[hawksight]

/lgtm

[hawksight]

/approve

[wallrj]

/approve

[jetstack-bot]

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