kep-3633-alt

README

KEP-3633 alternative

Overview

KEP-3633 is great and now under developing, but I need it NOW. Luckily, it's behavior can mimic with MutatingAdmissionWebhook.

So, I implement this according to KEP.

Roadmap and statuses

• Implement webhook
  • append .spec.affinity.podAffinity.required...Execution
  • append .spec.affinity.podAffinity.preferred...Execution
  • append .spec.affinity.podAntiAffinity.required...Execution
  • append .spec.affinity.podAntiAffinity.preferred...Execution
• Build and publish container image
  • published to ghcr.io/10hin/kep3633alt:latest
• Write installation manifest
  • Kustomize manifest (depends on cert-manager to provision webhook certificates)
  • Helm chart without dependencies to cert-manager

Install

Use helm with adding our repository:

helm repo add kep3633alt https://10hin.github.io/kep-3633-alt
helm repo update
helm upgrade -i -n kube-system kep3633alt kep3633alt/kep3633alt

Or without it:

helm upgrade -i -n kube-system kep3633alt kep3633alt --repo https://10hin.github.io/kep-3633-alt

Chart source is here.

Usage

After installation, deploy pods with pod affinity (or anti-affinity) configured not on spec but on annotations with JSON format.

If you have pod manifest (typically as pod template in deployment resource) using KEP3633 like following:

apiVersion: v1
kind: Pod
metadata:
  name: nginx
  labels:
    app: nginx
    pod-template-hash: UNEXPECTABLEVALUE
spec:
  affinity:
    podAntiAffinity:
      requiredDuringSchedulingIgnoredDuringExecution:
      - labelSelector:
          matchLabels:
            app: nginx
        topologyKey: topology.kubernetes.io/zone
        matchLabelKeys:
        - pod-template-hash
  # ...

above manifest may invalid for now. So, you can alternate it as follows:

apiVersion: v1
kind: Pod
metadata:
  annotations:
    kep-3633-alt.10h.in/podAntiAffinity.requiredDuringSchedulingIgnoredDuringExecution: |
      [
        {
          "labelSelector": {
            "matchLabels": {
              "app": "nginx"
            }
          },
          "topologyKey": "topology.kubernetes.io/zone",
          "matchLabelKeys": [
            "pod-template-hash"
          ]
        }
      ]
  name: nginx
  labels:
    app: nginx
    pod-template-hash: UNEXPECTABLEVALUE
spec:
  # ...

then it applied as follows:

apiVersion: v1
kind: Pod
metadata:
  annotations:
    kep-3633-alt.10h.in/podAntiAffinity.requiredDuringSchedulingIgnoredDuringExecution: |
      # reduced
  name: nginx
  labels:
    app: nginx
    pod-template-hash: UNEXPECTABLEVALUE
spec:
  affinity:
    podAntiAffinity:
      requiredDuringSchedulingIgnoredDuringExecution:
        - labelSelector:
            matchLabels:
              app: nginx
              pod-template-hash: UNEXPECTABLEVALUE
          topologyKey: topology.kubernetes.io/zone
  # ...

Usecases

see KEP3633