336 lines
18 KiB
Markdown
336 lines
18 KiB
Markdown
---
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title: 指定应用程序的中断预算（Disruption Budget）
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content_type: task
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weight: 110
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---
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<!-- ---
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title: Specifying a Disruption Budget for your Application
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content_type: task
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weight: 110
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--- -->
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<!-- overview -->
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<!-- This page shows how to limit the number of concurrent disruptions
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that your application experiences, allowing for higher availability
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while permitting the cluster administrator to manage the clusters
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nodes. -->
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本文展示了如何限制应用程序的并发中断数量，在允许集群管理员管理集群节点的同时保证高可用。
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## {{% heading "prerequisites" %}}
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<!-- * You are the owner of an application running on a Kubernetes cluster that requires
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high availability. -->
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* 用户是 Kubernetes 集群中有高可用需求的应用的所有者。
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<!-- * You should know how to deploy [Replicated Stateless Applications](/docs/tasks/run-application/run-stateless-application-deployment/)
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and/or [Replicated Stateful Applications](/docs/tasks/run-application/run-replicated-stateful-application/). -->
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* 用户应了解如何部署 [无状态应用](/docs/tasks/run-application/run-stateless-application-deployment/)
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和/或 [有状态应用](/docs/tasks/run-application/run-replicated-stateful-application/)。
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<!-- * You should have read about [Pod Disruptions](/docs/concepts/workloads/pods/disruptions/). -->
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* 用户应当已经阅读过关于 [Pod 中断](/docs/concepts/workloads/pods/disruptions/) 的文档。
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<!-- * You should confirm with your cluster owner or service provider that they respect
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Pod Disruption Budgets. -->
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* 用户应当与集群所有者或服务提供者确认其遵从 Pod 中断预算（Pod Disruption Budgets）的规则。
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<!-- steps -->
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<!-- ## Protecting an Application with a PodDisruptionBudget -->
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## 用 PodDisruptionBudget 来保护应用
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<!-- 1. Identify what application you want to protect with a PodDisruptionBudget (PDB).
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1. Think about how your application reacts to disruptions.
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1. Create a PDB definition as a YAML file.
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1. Create the PDB object from the YAML file. -->
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1. 确定想要使用 PodDisruptionBudget (PDB) 来保护的应用。
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1. 考虑应用对中断的反应。
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1. 以 YAML 文件形式定义 PDB 。
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1. 通过 YAML 文件创建 PDB 对象。
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<!-- discussion -->
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<!-- ## Identify an Application to Protect -->
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## 确定要保护的应用
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<!-- The most common use case when you want to protect an application
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specified by one of the built-in Kubernetes controllers: -->
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用户想要保护通过内置的 Kubernetes 控制器指定的应用，这是最常见的使用场景：
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- Deployment
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- ReplicationController
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- ReplicaSet
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- StatefulSet
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<!-- In this case, make a note of the controller's `.spec.selector`; the same
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selector goes into the PDBs `.spec.selector`. -->
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在这种情况下，在控制器的 `.spec.selector` 字段中做记录，并在 PDB 的 `.spec.selector` 字段中加入同样的选择器。
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<!-- You can also use PDBs with pods which are not controlled by one of the above
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controllers, or arbitrary groups of pods, but there are some restrictions,
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described in [Arbitrary Controllers and Selectors](#arbitrary-controllers-and-selectors). -->
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用户也可以用 PDB 来保护不受上述控制器控制的 pod，或任意组（arbitrary groups）的 pod， 但是正如 [任意控制器和选择器](#arbitrary-controllers-and-selectors) 中描述的，这里存在一些限制。
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<!-- ## Think about how your application reacts to disruptions -->
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## 考虑应用对中断的反应
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<!-- Decide how many instances can be down at the same time for a short period
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due to a voluntary disruption. -->
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确定在自发中断时，多少实例可以在短时间内同时关闭。
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<!-- - Stateless frontends:
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- Concern: don't reduce serving capacity by more than 10%.
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- Solution: use PDB with minAvailable 90% for example.
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- Single-instance Stateful Application:
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- Concern: do not terminate this application without talking to me.
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- Possible Solution 1: Do not use a PDB and tolerate occasional downtime.
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- Possible Solution 2: Set PDB with maxUnavailable=0. Have an understanding
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(outside of Kubernetes) that the cluster operator needs to consult you before
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termination. When the cluster operator contacts you, prepare for downtime,
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and then delete the PDB to indicate readiness for disruption. Recreate afterwards.
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- Multiple-instance Stateful application such as Consul, ZooKeeper, or etcd:
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- Concern: Do not reduce number of instances below quorum, otherwise writes fail.
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- Possible Solution 1: set maxUnavailable to 1 (works with varying scale of application).
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- Possible Solution 2: set minAvailable to quorum-size (e.g. 3 when scale is 5). (Allows more disruptions at once).
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- Restartable Batch Job:
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- Concern: Job needs to complete in case of voluntary disruption.
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- Possible solution: Do not create a PDB. The Job controller will create a replacement pod. -->
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- 无状态的前端：
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- 关注：不能降低服务能力 10% 以上。
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- 解决方案：例如，使用 PDB，指定其 minAvailable 值为 90%。
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- 单实例有状态应用：
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- 关注：不要在不通知的情况下终止该应用。
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- 可能的解决方案 1：不使用 PDB，并忍受偶尔的停机。
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- 可能的解决方案 2：设置 maxUnavailable=0 的 PDB。意为（Kubernetes 范畴之外的） 集群操作人员需要在终止应用前与用户协商，协商后准备停机，然后删除 PDB 表示准备中断，后续再重新创建。
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- 多实例有状态应用， 如 Consul、ZooKeeper 或 etcd：
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- 关注：不要将实例数量减少至低于仲裁规模（below quorum），否则将写入失败。
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- 可能的解决方案 1：设置 maxUnavailable 值为 1 (适用于不同规模的应用)。
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- 可能的解决方案 2：设置 minAvailable 值为仲裁规模（例如规模为 5 时设置为 3）。 (允许每次更多的中断)。
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- 可重新启动的批处理任务：
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- 关注： 自发中断的情况下，需要确保任务完成。
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- 可能的解决方案：不创建 PDB。 任务控制器会创建一个替换的 pod。
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<!-- ### Rounding logic when specifying percentages -->
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### 指定百分比时的舍入逻辑
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<!-- Values for `minAvailable` or `maxUnavailable` can be expressed as integers or as a percentage. -->
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`minAvailable` 或 `maxUnavailable` 的值可以表示为整数或百分比。
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<!-- - When you specify an integer, it represents a number of Pods. For instance, if you set `minAvailable` to 10, then 10
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Pods must always be available, even during a disruption. -->
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- 指定整数时，它表示许多Pod。 例如，如果将minAvailable设置为10，那么即使在中断期间，也必须始终有10个Pod可用。
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<!-- - When you specify a percentage by setting the value to a string representation of a percentage (eg. `"50%"`), it represents a percentage of
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total Pods. For instance, if you set `minUnavailable` to `"50%"`, then only 50% of the Pods can be unavailable during a
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disruption. -->
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- 通过将值设置为百分比的字符串表示形式（例如“50％”）来指定百分比时，它表示总 Pod 数的百分比。例如，如果将 "minUnavailable" 设置为“50％”，则只有50％的 Pod 可以中断。
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<!-- When you specify the value as a percentage, it may not map to an exact number of Pods. For example, if you have 7 Pods and
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you set `minAvailable` to `"50%"`, it's not immediately obvious whether that means 3 Pods or 4 Pods must be available.
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Kubernetes rounds up to the nearest integer, so in this case, 4 Pods must be available. You can examine the
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[code](https://github.com/kubernetes/kubernetes/blob/23be9587a0f8677eb8091464098881df939c44a9/pkg/controller/disruption/disruption.go#L539)
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that controls this behavior. -->
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如果将值指定为百分比，则可能无法映射到确切数量的 Pod 。例如，如果您有 7 个 Pod ，并且你将 `minAvailable` 设置为 `"50％"`，这不清楚是 3 个 Pod 或 4 个 Pod 必须可用。
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Kubernetes 向上取整到最接近的整数，因此在这种情况下，必须有 4 个 Pod 。
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您可以检查控制此行为的[代码](https://github.com/kubernetes/kubernetes/blob/23be9587a0f8677eb8091464098881df939c44a9/pkg/controller/disruption/disruption.go#L539)。
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<!-- ## Specifying a PodDisruptionBudget -->
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## 指定 PodDisruptionBudget
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<!-- A `PodDisruptionBudget` has three fields: -->
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一个 `PodDisruptionBudget` 有 3 个字段：
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<!-- * A label selector `.spec.selector` to specify the set of
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pods to which it applies. This field is required.
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* `.spec.minAvailable` which is a description of the number of pods from that
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set that must still be available after the eviction, even in the absence
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of the evicted pod. `minAvailable` can be either an absolute number or a percentage.
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* `.spec.maxUnavailable` (available in Kubernetes 1.7 and higher) which is a description
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of the number of pods from that set that can be unavailable after the eviction.
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It can be either an absolute number or a percentage. -->
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* 标签选择器 `.spec.selector` ，用于指定其所作用的 pod 集合， 该字段为必须字段。
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* `.spec.minAvailable` 表示驱逐后仍然保证可用的 pod 数量。即使因此影响到 pod 驱逐（即该条件在和 pod 驱逐发生冲突时优先保证）。
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`minAvailable` 值可以是绝对值，也可以是百分比。
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* `.spec.maxUnavailable` （Kubernetes 1.7 及更高的版本中可用）表示驱逐后允许不可用的 pod 的最大数量。
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其值可以是绝对值或是百分比。
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{{< note >}}
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<!-- For versions 1.8 and earlier: When creating a `PodDisruptionBudget`
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object using the `kubectl` command line tool, the `minAvailable` field has a
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default value of 1 if neither `minAvailable` nor `maxUnavailable` is specified. -->
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对于1.8及更早的版本：当你用 `kubectl` 命令行工具创建 `PodDisruptionBudget`对象时，如果既未指定 `minAvailable` 也未指定 `maxUnavailable`，
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则 `minAvailable` 字段有一个默认值1。
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{{< /note >}}
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<!-- You can specify only one of `maxUnavailable` and `minAvailable` in a single `PodDisruptionBudget`.
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`maxUnavailable` can only be used to control the eviction of pods
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that have an associated controller managing them. In the examples below, "desired replicas"
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is the `scale` of the controller managing the pods being selected by the
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`PodDisruptionBudget`. -->
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用户在同一个 `PodDisruptionBudget` 中只能够指定 `maxUnavailable` 和 `minAvailable` 中的一个。`maxUnavailable`
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只能够用于控制存在相应控制器的 pod 的驱逐（即不受控制器控制的 pod 不在 `maxUnavailable` 控制范围内）。在下面的示例中，
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“所需副本” 指的是相应控制器的 `scale`， 控制器对 `PodDisruptionBudget` 所选择的 pod 进行管理。
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<!-- Example 1: With a `minAvailable` of 5, evictions are allowed as long as they leave behind
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5 or more healthy pods among those selected by the PodDisruptionBudget's `selector`. -->
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示例 1：设置 `minAvailable` 值为 5 的情况下，驱逐时需保证 PodDisruptionBudget 的 `selector` 选中的 pod 中 5 个 或 5 个以上处于健康状态。
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<!-- Example 2: With a `minAvailable` of 30%, evictions are allowed as long as at least 30%
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of the number of desired replicas are healthy. -->
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示例 2：设置 `minAvailable` 值为 30% 的情况下，驱逐时需保证 pod 所需副本的至少 30% 处于健康状态。
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<!-- Example 3: With a `maxUnavailable` of 5, evictions are allowed as long as there are at most 5
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unhealthy replicas among the total number of desired replicas. -->
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示例 3：设置 `maxUnavailable` 值为 5 的情况下，驱逐时需保证所需副本中最多 5 个处于不可用状态。
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Example 4: With a `maxUnavailable` of 30%, evictions are allowed as long as no more than 30%
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of the desired replicas are unhealthy.
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示例4： 设置 `maxUnavailable` 值为 30% 的情况下，驱逐时需保证所需副本中最多 30% 处于不可用状态。
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<!-- In typical usage, a single budget would be used for a collection of pods managed by
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a controller—for example, the pods in a single ReplicaSet or StatefulSet. -->
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在典型用法中，中断预算会被用于一个控制器管理的一组 pod 中——例如：一个 ReplicaSet 或 StatefulSet 中的 pod。
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{{< note >}}
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<!-- A disruption budget does not truly guarantee that the specified
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number/percentage of pods will always be up. For example, a node that hosts a
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pod from the collection may fail when the collection is at the minimum size
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specified in the budget, thus bringing the number of available pods from the
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collection below the specified size. The budget can only protect against
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voluntary evictions, not all causes of unavailability. -->
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注意：中断预算并不能真正保证指定数量/百分比的 pod 一直处于运行状态。例如： 当 pod 集合的
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规模处于预算指定的最小值时，承载集合中某个 pod 的节点发生了故障，这样就导致集合中可用 pod 的
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数量低于预算指定值。预算只能够针对自发的驱逐提供保护，而不能针对所有 pod 不可用的诱因。
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{{< /note >}}
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<!-- A `maxUnavailable` of 0% (or 0) or a `minAvailable` of 100% (or equal to the
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number of replicas) may block node drains entirely. This is permitted as per the
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semantics of `PodDisruptionBudget`. -->
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设置 `maxUnavailable` 值为 0% （或 0 ）或设置 `minAvailable` 值为 100% （或等于副本数） 可能会
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阻塞节点，导致资源耗尽。按照 `PodDisruptionBudget` 的语义，这是允许的。
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<!-- You can find examples of pod disruption budgets defined below. They match pods with the label
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`app: zookeeper`. -->
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用户可以在下面看到 pod 中断预算定义的示例，它们与带有 `app: zookeeper` 标签的 pod 相匹配：
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<!-- Example PDB Using minAvailable: -->
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使用 minAvailable 的PDB 示例：
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{{< codenew file="policy/zookeeper-pod-disruption-budget-minavailable.yaml" >}}
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<!-- Example PDB Using maxUnavailable (Kubernetes 1.7 or higher): -->
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使用 maxUnavailable 的 PDB 示例（Kubernetes 1.7 或更高的版本）：
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{{< codenew file="policy/zookeeper-pod-disruption-budget-maxunavailable.yaml" >}}
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<!-- For example, if the above `zk-pdb` object selects the pods of a StatefulSet of size 3, both
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specifications have the exact same meaning. The use of `maxUnavailable` is recommended as it
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automatically responds to changes in the number of replicas of the corresponding controller. -->
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例如，如果上述 `zk-pdb` 选择的是一个规格为 3 的 StatefulSet 对应的 pod，那么上面两种规范的含义完全相同。
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推荐使用 `maxUnavailable` ，因为它自动响应控制器副本数量的变化。
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## Create the PDB object
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## 创建 PDB 对象
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<!-- You can create the PDB object with a command like `kubectl apply -f mypdb.yaml`. -->
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用户可以通过类似 `kubectl create -f mypdb.yaml` 的命令来创建 PDB。
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<!-- You cannot update PDB objects. They must be deleted and re-created. -->
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PDB 对象无法更新，必须删除后重新创建。
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## Check the status of the PDB
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## 检查 PDB 的状态
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<!-- Use kubectl to check that your PDB is created. -->
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使用 kubectl 来确认 PDB 被创建。
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<!-- Assuming you don't actually have pods matching `app: zookeeper` in your namespace,
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then you'll see something like this: -->
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假设用户的名字空间下没有匹配 `app: zookeeper` 的 pod，用户会看到类似下面的信息：
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```shell
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kubectl get poddisruptionbudgets
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```
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```
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NAME MIN-AVAILABLE ALLOWED-DISRUPTIONS AGE
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zk-pdb 2 0 7s
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```
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<!-- If there are matching pods (say, 3), then you would see something like this: -->
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假设有匹配的 pod (比如说 3 个), 那么用户会看到类似下面的信息：
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```shell
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kubectl get poddisruptionbudgets
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```
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```
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NAME MIN-AVAILABLE ALLOWED-DISRUPTIONS AGE
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zk-pdb 2 1 7s
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```
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<!-- The non-zero value for `ALLOWED-DISRUPTIONS` means that the disruption controller has seen the pods,
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counted the matching pods, and updated the status of the PDB. -->
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`ALLOWED-DISRUPTIONS` 值非 0 意味着中断控制器已经感知到相应的 pod， 对匹配的 pod 进行统计，并更新了 PDB 的状态。
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<!-- You can get more information about the status of a PDB with this command: -->
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用户可以通过以下命令获取更多 PDB 状态相关信息：
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```shell
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kubectl get poddisruptionbudgets zk-pdb -o yaml
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```
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```yaml
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apiVersion: policy/v1beta1
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kind: PodDisruptionBudget
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metadata:
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creationTimestamp: 2017-08-28T02:38:26Z
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generation: 1
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name: zk-pdb
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…
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status:
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currentHealthy: 3
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desiredHealthy: 3
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disruptedPods: null
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disruptionsAllowed: 1
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expectedPods: 3
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observedGeneration: 1
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```
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<!-- ## Arbitrary Controllers and Selectors -->
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## 任意控制器和选择器
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<!-- You can skip this section if you only use PDBs with the built-in
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application controllers (Deployment, ReplicationController, ReplicaSet, and StatefulSet),
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with the PDB selector matching the controller's selector. -->
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如果用户只使用与内置的应用控制器（Deployment、ReplicationController、ReplicaSet 和 StatefulSet）
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对应的 PDB，也就是 PDB 的选择器与 控制器的选择器相匹配，那么可以跳过这一节。
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<!-- You can use a PDB with pods controlled by another type of controller, by an
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"operator", or bare pods, but with these restrictions: -->
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用户可以使用这样的 PDB：它对应的 pod 可能由其他类型的控制器控制，可能由 "operator" 控制，
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也可能为“裸的（不受控制器控制）” pod，但该类 PDB 存在以下限制：
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- only `.spec.minAvailable` can be used, not `.spec.maxUnavailable`.
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- only an integer value can be used with `.spec.minAvailable`, not a percentage.
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- 只能够使用 `.spec.minAvailable` ，而不能够使用 `.spec.maxUnavailable。`
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- 只能够使用整数作为 `.spec.minAvailable` 的值，而不能使用百分比。
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<!-- You can use a selector which selects a subset or superset of the pods belonging to a built-in
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controller. However, when there are multiple PDBs in a namespace, you must be careful not
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to create PDBs whose selectors overlap. -->
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用户可以令选择器选择一个内置控制器所控制 pod 的子集或父集。然而，当名字空间下存在多个 PDB 时，
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用户必须小心，保证 PDB 的选择器之间不重叠。
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