28 lines
1.6 KiB
Markdown
28 lines
1.6 KiB
Markdown
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# K8S Deployment Enhancements
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## Controlling pod placement
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The placement of pods created as part of a stack deployment can be controlled to either avoid certain nodes, or require certain nodes.
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### Pod/Node Affinity
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Node affinity rules applied to pods target node labels. The effect is that a pod can only be placed on a node having the specified label value. Note that other pods that do not have any node affinity rules can also be placed on those same nodes. Thus node affinity for a pod controls where that pod can be placed, but does not control where other pods are placed.
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Node affinity for stack pods is specified in the deployment's `spec.yml` file as follows:
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```
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node-affinities:
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- label: nodetype
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value: typeb
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```
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This example denotes that the stack's pods should only be placed on nodes that have the label `nodetype` with value `typeb`.
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### Node Taint Toleration
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K8s nodes can be given one or more "taints". These are special fields (distinct from labels) with a name (key) and optional value.
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When placing pods, the k8s scheduler will only assign a pod to a tainted node if the pod posesses a corresponding "toleration".
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This is metadata associated with the pod that specifies that the pod "tolerates" a given taint.
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Therefore taint toleration provides a mechanism by which only certain pods can be placed on specific nodes, and provides a complementary mechanism to node affinity.
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Taint toleration for stack pods is specified in the deployment's `spec.yml` file as follows:
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```
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node-tolerations:
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- key: nodetype
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value: typeb
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```
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This example denotes that the stack's pods will tolerate a taint: `nodetype=typeb`
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