Update "node selection" documentation to reflect Beta affinity syntax
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Kevin
Andrew Chen
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855cc67c77
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@ -77,16 +77,16 @@ with a standard set of labels. As of Kubernetes v1.4 these labels are
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* `beta.kubernetes.io/os`
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* `beta.kubernetes.io/arch`
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## Alpha features: affinity and anti-affinity
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## Beta features: affinity and anti-affinity
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`nodeSelector` provides a very simple way to constrain pods to nodes with particular labels. The affinity/anti-affinity
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feature, currently in alpha, greatly expands the types of constraints you can express. The key enhancements are
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feature, currently in beta, greatly expands the types of constraints you can express. The key enhancements are
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1. the language is more expressive (not just "AND of exact match")
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1. you can indicate that the rule is "soft"/"preference" rather than a hard requirement, so if the scheduler
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can't satisfy it, the pod will still be scheduled
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1. you can constrain against labels on other pods running on the node (or other topological domain),
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rather than against labels on the node itself, which allows rules about which pods can and cannot be co-located
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2. you can indicate that the rule is "soft"/"preference" rather than a hard requirement, so if the scheduler
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can't satisfy it, the pod will still be scheduled
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3. you can constrain against labels on other pods running on the node (or other topological domain),
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rather than against labels on the node itself, which allows rules about which pods can and cannot be co-located
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The affinity feature consists of two types of affinity, "node affinity" and "inter-pod affinity/anti-affinity."
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Node affinity is like the existing `nodeSelector` (but with the first two benefits listed above),
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@ -96,7 +96,7 @@ described in the third item listed above, in addition to having the first and se
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`nodeSelector` continues to work as usual, but will eventually be deprecated, as node affinity can express
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everything that `nodeSelector` can express.
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### Node affinity (alpha feature)
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### Node affinity (beta feature)
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Node affinity was introduced in Kubernetes 1.2.
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Node affinity is conceptually similar to `nodeSelector` -- it allows you to constrain which nodes your
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@ -116,7 +116,7 @@ Thus an example of `requiredDuringSchedulingIgnoredDuringExecution` would be "on
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and an example `preferredDuringSchedulingIgnoredDuringExecution` would be "try to run this set of pods in availability
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zone XYZ, but if it's not possible, then allow some to run elsewhere".
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Node affinity is currently expressed using an annotation on Pod. Once the feature goes to GA it will use a field of Pod.
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Node affinity is specified as field `nodeAffinity` of `affinity` in the PodSpec.
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Here's an example of a pod that uses node affinity:
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@ -124,8 +124,8 @@ Here's an example of a pod that uses node affinity:
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This node affinity rule says the pod can only be placed on a node with a label whose key is
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`kubernetes.io/e2e-az-name` and whose value is either `e2e-az1` or `e2e-az2`. In addition,
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among nodes that meet that criteria, nodes with a label whose key is `another-annotation-key` and whose
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value is `another-annotation-value` should be preferred.
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among nodes that meet that criteria, nodes with a label whose key is `another-node-label-key` and whose
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value is `another-node-label-value` should be preferred.
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You can see the operator `In` being used in the example. The new node affinity syntax supports the following operators: `In`, `NotIn`, `Exists`, `DoesNotExist`, `Gt`, `Lt`.
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There is no explicit "node anti-affinity" concept, but `NotIn` and `DoesNotExist` give that behavior.
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@ -136,7 +136,7 @@ to be scheduled onto a candidate node.
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For more information on node affinity, see the design doc
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[here](https://github.com/kubernetes/kubernetes/blob/{{page.githubbranch}}/docs/design/nodeaffinity.md).
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### Inter-pod affinity and anti-affinity (alpha feature)
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### Inter-pod affinity and anti-affinity (beta feature)
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Inter-pod affinity and anti-affinity were introduced in Kubernetes 1.4.
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Inter-pod affinity and anti-affinity allow you to constrain which nodes your pod is eligible to schedule on *based on
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@ -157,13 +157,14 @@ in the same zone, since they communicate a lot with each other"
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and an example `preferredDuringSchedulingIgnoredDuringExecution` anti-affinity would be "spread the pods from this service across zones"
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(a hard requirement wouldn't make sense, since you probably have more pods than zones).
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Inter-pod affinity and anti-affinity are currently expressed using an annotation on Pod. Once the feature goes to GA it will use a field.
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Inter-pod affinity is specified as field `podAffinity` of `affinity` in the PodSpec.
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And inter-pod anti-affinity is specified as field `podAntiAffinity` of `affinity`.
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Here's an example of a pod that uses pod affinity:
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{% include code.html language="yaml" file="pod-with-pod-affinity.yaml" ghlink="/docs/user-guide/node-selection/pod-with-pod-affinity.yaml" %}
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The affinity annotation on this pod defines one pod affinity rule and one pod anti-affinity rule. Both
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The affinity on this pod defines one pod affinity rule and one pod anti-affinity rule. Both
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must be satisfied for the pod to schedule onto a node. The
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pod affinity rule says that the pod can schedule onto a node only if that node is in the same zone
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as at least one already-running pod that has a label with key "security" and value "S1". (More precisely, the pod is eligible to run
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@ -2,27 +2,25 @@ apiVersion: v1
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kind: Pod
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metadata:
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name: with-node-affinity
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annotations:
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scheduler.alpha.kubernetes.io/affinity: >
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{
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"nodeAffinity": {
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"requiredDuringSchedulingIgnoredDuringExecution": {
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"nodeSelectorTerms": [
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{
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"matchExpressions": [
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{
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"key": "kubernetes.io/e2e-az-name",
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"operator": "In",
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"values": ["e2e-az1", "e2e-az2"]
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}
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]
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}
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]
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}
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}
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}
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another-annotation-key: another-annotation-value
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spec:
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affinity:
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nodeAffinity:
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requiredDuringSchedulingIgnoredDuringExecution:
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nodeSelectorTerms:
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- matchExpressions:
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- key: kubernetes.io/e2e-az-name
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operator: In
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values:
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- e2e-az1
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- e2e-az2
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preferredDuringSchedulingIgnoredDuringExecution:
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- weight: 1
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preference:
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matchExpressions:
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- key: another-node-label-key
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operator: In
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values:
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- another-node-label-value
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containers:
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- name: with-node-affinity
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image: gcr.io/google_containers/pause:2.0
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image: gcr.io/google_containers/pause:2.0
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@ -2,43 +2,26 @@ apiVersion: v1
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kind: Pod
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metadata:
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name: with-pod-affinity
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annotations:
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scheduler.alpha.kubernetes.io/affinity: >
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{
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"podAffinity": {
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"requiredDuringSchedulingIgnoredDuringExecution": [
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{
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"labelSelector": {
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"matchExpressions": [
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{
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"key": "security",
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"operator": "In",
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"values": ["S1"]
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}
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]
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},
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"topologyKey": "failure-domain.beta.kubernetes.io/zone"
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}
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]
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},
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"podAntiAffinity": {
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"requiredDuringSchedulingIgnoredDuringExecution": [
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{
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"labelSelector": {
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"matchExpressions": [
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{
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"key": "security",
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"operator": "In",
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"values": ["S2"]
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}
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]
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},
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"topologyKey": "kubernetes.io/hostname"
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}
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]
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}
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}
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spec:
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affinity:
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podAffinity:
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requiredDuringSchedulingIgnoredDuringExecution:
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- labelSelector:
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matchExpressions:
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- key: security
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operator: In
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values:
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- S1
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topologyKey: failure-domain.beta.kubernetes.io/zone
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podAntiAffinity:
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requiredDuringSchedulingIgnoredDuringExecution:
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- labelSelector:
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matchExpressions:
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- key: security
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operator: In
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values:
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- S2
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topologyKey: kubernetes.io/hostname
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containers:
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- name: with-pod-affinity
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image: gcr.io/google_containers/pause:2.0
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