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c52f07b615
* new samples; updates * typos * add policy to restrict LoadBalancer * correct sample numbering * fix typos
75 lines
2.4 KiB
Markdown
75 lines
2.4 KiB
Markdown
# Spread pods across topology
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When having a Kubernetes cluster that spans multiple availability zones, it is often desired to spread your Pods out among them in a way which controls where they land. This can be advantageous in ensuring that, should one of those zones fail, your application continues to run in a more predictable way and with less potential loss.
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This sample policy configures all Deployments having the label of `required: true` to be spread amongst hosts which are labeled with the key name of `zone`. It does this only to Deployments which do not already have the field `topologySpreadConstraints` set.
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**NOTE:** When deploying this policy to a Kubernetes cluster less than version 1.19, some feature gate flags will need to be enabled. Please see the [More Information](#more-information) section below.
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In order to test the policy, you can use this sample Deployment manifest below.
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```yaml
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apiVersion: apps/v1
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kind: Deployment
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metadata:
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labels:
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app: busybox
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distributed: required
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name: busybox
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spec:
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replicas: 2
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selector:
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matchLabels:
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app: busybox
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distributed: required
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template:
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metadata:
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labels:
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app: busybox
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distributed: required
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spec:
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containers:
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- image: busybox:1.28
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name: busybox
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command: ["sleep", "9999"]
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```
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## More Information
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* [Pod Topology Spread Constraints](https://kubernetes.io/docs/concepts/workloads/pods/pod-topology-spread-constraints/)
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## Policy YAML
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[spread_pods_across_topology.yaml](more/spread_pods_across_topology.yaml)
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```yaml
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apiVersion: kyverno.io/v1
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kind: ClusterPolicy
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metadata:
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name: spread-pods
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spec:
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rules:
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- name: spread-pods-across-nodes
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# Matches any Deployment with the label `distributed=required`
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match:
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resources:
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kinds:
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- Deployment
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selector:
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matchLabels:
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distributed: required
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# Mutates the incoming Deployment.
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mutate:
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patchStrategicMerge:
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spec:
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template:
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spec:
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# Adds the topologySpreadConstraints field if non-existent in the request.
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+(topologySpreadConstraints):
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- maxSkew: 1
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topologyKey: zone
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whenUnsatisfiable: DoNotSchedule
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labelSelector:
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matchLabels:
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distributed: required
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```
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