[zh] Add a blog: 2024-08-16-matchlabelkeys-podaffinity.md
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layout: blog
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title: 'Kubernetes 1.31：podAffinity 中的 matchLabelKeys 进阶至 Beta'
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date: 2024-08-16
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slug: matchlabelkeys-podaffinity
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author: >
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Kensei Nakada (Tetrate)
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---
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<!--
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layout: blog
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title: 'Kubernetes 1.31: MatchLabelKeys in PodAffinity graduates to beta'
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date: 2024-08-16
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slug: matchlabelkeys-podaffinity
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author: >
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Kensei Nakada (Tetrate)
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-->
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<!--
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Kubernetes 1.29 introduced new fields `MatchLabelKeys` and `MismatchLabelKeys` in PodAffinity and PodAntiAffinity.
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In Kubernetes 1.31, this feature moves to beta and the corresponding feature gate (`MatchLabelKeysInPodAffinity`) gets enabled by default.
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-->
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Kubernetes 1.29 在 podAffinity 和 podAntiAffinity 中引入了新的字段 `matchLabelKeys` 和 `mismatchLabelKeys`。
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在 Kubernetes 1.31 中，此特性进阶至 Beta，并且相应的特性门控（`MatchLabelKeysInPodAffinity`）默认启用。
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<!--
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## `MatchLabelKeys` - Enhanced scheduling for versatile rolling updates
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During a workload's (e.g., Deployment) rolling update, a cluster may have Pods from multiple versions at the same time.
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However, the scheduler cannot distinguish between old and new versions based on the `LabelSelector` specified in PodAffinity or PodAntiAffinity. As a result, it will co-locate or disperse Pods regardless of their versions.
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-->
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## `matchLabelKeys` - 为多样化滚动更新增强了调度
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在工作负载（例如 Deployment）的滚动更新期间，集群中可能同时存在多个版本的 Pod。
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然而，调度器无法基于 podAffinity 或 podAntiAffinity 中指定的 `labelSelector` 区分新旧版本。
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结果，调度器将并置或分散调度 Pod，不会考虑这些 Pod 的版本。
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<!--
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This can lead to sub-optimal scheduling outcome, for example:
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- New version Pods are co-located with old version Pods (PodAffinity), which will eventually be removed after rolling updates.
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- Old version Pods are distributed across all available topologies, preventing new version Pods from finding nodes due to PodAntiAffinity.
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-->
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这可能导致次优的调度结果，例如：
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- 新版本的 Pod 与旧版本的 Pod（podAffinity）并置在一起，这些旧版本的 Pod 最终将在滚动更新后被移除。
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- 旧版本的 Pod 被分布在所有可用的拓扑中，导致新版本的 Pod 由于 podAntiAffinity 无法找到节点。
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<!--
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`MatchLabelKeys` is a set of Pod label keys and addresses this problem.
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The scheduler looks up the values of these keys from the new Pod's labels and combines them with `LabelSelector`
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so that PodAffinity matches Pods that have the same key-value in labels.
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By using label [pod-template-hash](/docs/concepts/workloads/controllers/deployment/#pod-template-hash-label) in `MatchLabelKeys`,
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you can ensure that only Pods of the same version are evaluated for PodAffinity or PodAntiAffinity.
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-->
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`matchLabelKeys` 是一组 Pod 标签键，可以解决上述问题。
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调度器从新 Pod 的标签中查找这些键的值，并将其与 `labelSelector` 结合，
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以便 podAffinity 匹配到具有相同标签键值的 Pod。
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通过在 `matchLabelKeys` 中使用标签
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[pod-template-hash](/zh-cn/docs/concepts/workloads/controllers/deployment/#pod-template-hash-label)，
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你可以确保对 podAffinity 或 podAntiAffinity 进行评估时仅考虑相同版本的 Pod。
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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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name: application-server
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...
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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: app
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operator: In
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values:
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- database
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topologyKey: topology.kubernetes.io/zone
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matchLabelKeys:
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- pod-template-hash
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```
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<!--
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The above matchLabelKeys will be translated in Pods like:
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-->
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上述 Pod 中的 `matchLabelKeys` 将被转换为：
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<!--
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# Added from matchLabelKeys; Only Pods from the same replicaset will match this affinity.
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-->
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```yaml
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kind: Pod
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metadata:
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name: application-server
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labels:
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pod-template-hash: xyz
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...
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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: app
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operator: In
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values:
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- database
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- key: pod-template-hash # 从 matchLabelKeys 添加; 只有来自同一 ReplicaSet 的 Pod 将与此亲和性匹配
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operator: In
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values:
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- xyz
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topologyKey: topology.kubernetes.io/zone
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matchLabelKeys:
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- pod-template-hash
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```
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<!--
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## `MismatchLabelKeys` - Service isolation
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`MismatchLabelKeys` is a set of Pod label keys, like `MatchLabelKeys`,
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which looks up the values of these keys from the new Pod's labels, and merge them with `LabelSelector` as `key notin (value)`
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so that PodAffinity does _not_ match Pods that have the same key-value in labels.
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Suppose all Pods for each tenant get `tenant` label via a controller or a manifest management tool like Helm.
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-->
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## `mismatchLabelKeys` - 服务隔离
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`mismatchLabelKeys` 是一组 Pod 标签键，类似于 `matchLabelKeys`，
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它在新 Pod 的标签中查找这些键的值，并将其与 `labelSelector` 合并为 `key notin (value)`，
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以便 podAffinity **不**会匹配到具有相同标签键值的 Pod。
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假设每个租户的所有 Pod 通过控制器或像 Helm 这样的清单管理工具得到 `tenant` 标签。
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<!--
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Although the value of `tenant` label is unknown when composing each workload's manifest,
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the cluster admin wants to achieve exclusive 1:1 tenant to domain placement for a tenant isolation.
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`MismatchLabelKeys` works for this usecase;
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By applying the following affinity globally using a mutating webhook,
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the cluster admin can ensure that the Pods from the same tenant will land on the same domain exclusively,
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meaning Pods from other tenants won't land on the same domain.
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-->
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尽管在组合每个工作负载的清单时，`tenant` 标签的值是未知的，
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但集群管理员希望实现租户与域之间形成排他性的 1:1 对应关系，以便隔离租户。
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`mismatchLabelKeys` 适用于这一使用场景；
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通过使用变更性质的 Webhook 在全局应用以下亲和性，
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集群管理员可以确保来自同一租户的 Pod 将以独占方式落到同一域上，
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这意味着来自其他租户的 Pod 不会落到同一域上。
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<!--
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# ensures the pods of this tenant land on the same node pool
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# ensures only Pods from this tenant lands on the same node pool
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-->
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```yaml
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affinity:
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podAffinity: # 确保此租户的 Pod 落在同一节点池上
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requiredDuringSchedulingIgnoredDuringExecution:
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- matchLabelKeys:
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- tenant
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topologyKey: node-pool
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podAntiAffinity: # 确保只有此租户的 Pod 落在同一节点池上
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requiredDuringSchedulingIgnoredDuringExecution:
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- mismatchLabelKeys:
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- tenant
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labelSelector:
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matchExpressions:
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- key: tenant
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operator: Exists
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topologyKey: node-pool
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```
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<!--
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The above matchLabelKeys and mismatchLabelKeys will be translated to like:
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-->
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上述的 `matchLabelKeys` 和 `mismatchLabelKeys` 将被转换为：
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<!--
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# ensures the pods of this tenant land on the same node pool
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# ensures only Pods from this tenant lands on the same node pool
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-->
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```yaml
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kind: Pod
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metadata:
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name: application-server
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labels:
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tenant: service-a
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spec:
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affinity:
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podAffinity: # 确保此租户的 Pod 落在同一节点池上
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requiredDuringSchedulingIgnoredDuringExecution:
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- matchLabelKeys:
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- tenant
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topologyKey: node-pool
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labelSelector:
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matchExpressions:
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- key: tenant
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operator: In
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values:
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- service-a
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podAntiAffinity: # 确保只有此租户的 Pod 落在同一节点池上
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requiredDuringSchedulingIgnoredDuringExecution:
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- mismatchLabelKeys:
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- tenant
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labelSelector:
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matchExpressions:
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- key: tenant
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operator: Exists
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- key: tenant
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operator: NotIn
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values:
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- service-a
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topologyKey: node-pool
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```
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<!--
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## Getting involved
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These features are managed by Kubernetes [SIG Scheduling](https://github.com/kubernetes/community/tree/master/sig-scheduling).
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Please join us and share your feedback. We look forward to hearing from you!
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-->
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## 参与其中
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这些特性由 Kubernetes
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[SIG Scheduling](https://github.com/kubernetes/community/tree/master/sig-scheduling) 管理。
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请加入我们并分享你的反馈。我们期待听到你的声音！
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<!--
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## How can I learn more?
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- [The official document of PodAffinity](/docs/concepts/scheduling-eviction/assign-pod-node/#inter-pod-affinity-and-anti-affinity)
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- [KEP-3633: Introduce MatchLabelKeys and MismatchLabelKeys to PodAffinity and PodAntiAffinity](https://github.com/kubernetes/enhancements/blob/master/keps/sig-scheduling/3633-matchlabelkeys-to-podaffinity/README.md#story-2)
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-->
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## 了解更多
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- [podAffinity 的官方文档](/zh-cn/docs/concepts/scheduling-eviction/assign-pod-node/#inter-pod-affinity-and-anti-affinity)
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- [KEP-3633：将 matchLabelKeys 和 mismatchLabelKeys 引入 podAffinity 和 podAntiAffinity](https://github.com/kubernetes/enhancements/blob/master/keps/sig-scheduling/3633-matchlabelkeys-to-podaffinity/README.md#story-2)
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