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[zh] Localize docs/concepts/services-networking/cluster-ip-allocation.md
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‎content/zh-cn/docs/concepts/services-networking/cluster-ip-allocation.md

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---
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title: Service ClusterIP 分配
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content_type: concept
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weight: 120
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---
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<!--
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reviewers:
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- sftim
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- thockin
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title: Service ClusterIP allocation
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content_type: concept
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weight: 120
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-->
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<!-- overview -->
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<!--
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In Kubernetes, [Services](/docs/concepts/services-networking/service/) are an abstract way to expose
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an application running on a set of Pods. Services
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can have a cluster-scoped virtual IP address (using a Service of `type: ClusterIP`).
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Clients can connect using that virtual IP address, and Kubernetes then load-balances traffic to that
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Service across the different backing Pods.
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-->
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在 Kubernetes 中，[Service](/zh-cn/docs/concepts/services-networking/service/) 是一种抽象的方式，
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用于公开在一组 Pod 上运行的应用。
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Service 可以具有集群作用域的虚拟 IP 地址（使用 `type: ClusterIP` 的 Service）。
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客户端可以使用该虚拟 IP 地址进行连接，Kubernetes 通过不同的后台 Pod 对该 Service 的流量进行负载均衡。
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<!-- body -->
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<!--
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## How Service ClusterIPs are allocated?
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When Kubernetes needs to assign a virtual IP address for a Service,
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that assignment happens one of two ways:
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_dynamically_
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: the cluster's control plane automatically picks a free IP address from within the configured IP range for `type: ClusterIP` Services.
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_statically_
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: you specify an IP address of your choice, from within the configured IP range for Services.
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Across your whole cluster, every Service `ClusterIP` must be unique.
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Trying to create a Service with a specific `ClusterIP` that has already
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been allocated will return an error.
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-->
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## Service ClusterIP 是如何分配的？
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当 Kubernetes 需要为 Service 分配虚拟 IP 地址时，该分配会通过以下两种方式之一进行：
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**动态分配**
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: 集群的控制面自动从所配置的 IP 范围内为 `type: ClusterIP` 选择一个空闲 IP 地址。
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**静态分配**
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: 根据为 Service 所配置的 IP 范围，选定并设置你的 IP 地址。
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在整个集群中，每个 Service 的 `ClusterIP` 都必须是唯一的。
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尝试使用已分配的 `ClusterIP` 创建 Service 将返回错误。
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<!--
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## Why do you need to reserve Service Cluster IPs?
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Sometimes you may want to have Services running in well-known IP addresses, so other components and
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users in the cluster can use them.
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The best example is the DNS Service for the cluster. As a soft convention, some Kubernetes installers assign the 10th IP address from
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the Service IP range to the DNS service. Assuming you configured your cluster with Service IP range
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10.96.0.0/16 and you want your DNS Service IP to be 10.96.0.10, you'd have to create a Service like
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this:
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-->
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## 为什么需要预留 Service 的 ClusterIP ？
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有时你可能希望 Services 在众所周知的 IP 上面运行，以便集群中的其他组件和用户可以使用它们。
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最好的例子是集群的 DNS Service。作为一种非强制性的约定，一些 Kubernetes 安装程序
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将 Service IP 范围中的第 10 个 IP 地址分配给 DNS 服务。假设将集群的 Service IP 范围配置为
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10.96.0.0/16，并且希望 DNS Service IP 为 10.96.0.10，则必须创建如下 Service：
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```yaml
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apiVersion: v1
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kind: Service
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metadata:
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labels:
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k8s-app: kube-dns
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kubernetes.io/cluster-service: "true"
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kubernetes.io/name: CoreDNS
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name: kube-dns
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namespace: kube-system
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spec:
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clusterIP: 10.96.0.10
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ports:
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- name: dns
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port: 53
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protocol: UDP
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targetPort: 53
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- name: dns-tcp
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port: 53
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protocol: TCP
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targetPort: 53
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selector:
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k8s-app: kube-dns
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type: ClusterIP
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```
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<!--
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but as it was explained before, the IP address 10.96.0.10 has not been reserved; if other Services are created
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before or in parallel with dynamic allocation, there is a chance they can allocate this IP, hence,
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you will not be able to create the DNS Service because it will fail with a conflict error.
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-->
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但如前所述，IP 地址 10.96.0.10 尚未被保留。如果在 DNS 启动之前或同时采用动态分配机制创建其他 Service，
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则它们有可能被分配此 IP，因此，你将无法创建 DNS Service，因为它会因冲突错误而失败。
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<!--
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## How can you avoid Service ClusterIP conflicts? {#avoid-ClusterIP-conflict}
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The allocation strategy implemented in Kubernetes to allocate ClusterIPs to Services reduces the
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risk of collision.
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The `ClusterIP` range is divided, based on the formula `min(max(16, cidrSize / 16), 256)`,
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described as _never less than 16 or more than 256 with a graduated step between them_.
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Dynamic IP assignment uses the upper band by default, once this has been exhausted it will
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use the lower range. This will allow users to use static allocations on the lower band with a low
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risk of collision.
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-->
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## 如何避免 Service ClusterIP 冲突？{#avoid-ClusterIP-conflict}
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Kubernetes 中用來将 ClusterIP 分配给 Service 的分配策略降低了冲突的风险。
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`ClusterIP` 范围根据公式 `min(max(16, cidrSize / 16), 256)` 进行划分，
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描述为不小于 16 且不大于 256，并在二者之间有一个渐进的步长。
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默认情况下，动态 IP 分配使用地址较高的一段，一旦用完，它将使用较低范围。
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这将允许用户在冲突风险较低的较低地址段上使用静态分配。
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<!--
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## Examples {#allocation-examples}
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-->
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## 示例 {#allocation-examples}
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<!--
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### Example 1 {#allocation-example-1}
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This example uses the IP address range: 10.96.0.0/24 (CIDR notation) for the IP addresses
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of Services.
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-->
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### 示例 1 {#allocation-example-1}
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此示例使用 IP 地址范围：10.96.0.0/24（CIDR 表示法）作为 Service 的 IP 地址。
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<!--
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Range Size: 2<sup>8</sup> - 2 = 254
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Band Offset: `min(max(16, 256/16), 256)` = `min(16, 256)` = 16
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Static band start: 10.96.0.1
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Static band end: 10.96.0.16
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Range end: 10.96.0.254
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{{< mermaid >}}
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pie showData
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title 10.96.0.0/24
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"Static" : 16
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"Dynamic" : 238
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{{< /mermaid >}}
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-->
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范围大小：2<sup>8</sup> - 2 = 254
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带宽偏移量：`min(max(16, 256/16), 256)` = `min(16, 256)` = 16
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静态带宽起始地址：10.96.0.1
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静态带宽结束地址：10.96.0.16
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范围结束地址：10.96.0.254
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{{< mermaid >}}
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pie showData
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title 10.96.0.0/24
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"静态分配" : 16
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"动态分配" : 238
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{{< /mermaid >}}
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<!--
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### Example 2 {#allocation-example-2}
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This example uses the IP address range: 10.96.0.0/20 (CIDR notation) for the IP addresses
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of Services.
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-->
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### 示例 2 {#allocation-example-2}
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此示例使用 IP 地址范围 10.96.00/20（CIDR 表示法）作为 Service 的 IP 地址。
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<!--
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Range Size: 2<sup>12</sup> - 2 = 4094
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Band Offset: `min(max(16, 4096/16), 256)` = `min(256, 256)` = 256
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Static band start: 10.96.0.1
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Static band end: 10.96.1.0
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Range end: 10.96.15.254
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{{< mermaid >}}
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pie showData
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title 10.96.0.0/20
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"Static" : 256
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"Dynamic" : 3838
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{{< /mermaid >}}
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-->
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范围大小：2<sup>12</sup> - 2 = 4094
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带宽偏移量：`min(max(16, 4096/16), 256)` = `min(256, 256)` = 256
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静态带宽起始地址：10.96.0.1
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静态带宽结束地址：10.96.1.0
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范围结束地址：10.96.15.254
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{{< mermaid >}}
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pie showData
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title 10.96.0.0/20
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"静态分配" : 256
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"动态分配" : 3838
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{{< /mermaid >}}
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<!--
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### Example 3 {#allocation-example-3}
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This example uses the IP address range: 10.96.0.0/16 (CIDR notation) for the IP addresses
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of Services.
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-->
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### 示例 3 {#allocation-example-3}
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此示例使用 IP 地址范围 10.96.0.0/16（CIDR 表示法）作为 Service 的 IP 地址。
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<!--
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Range Size: 2<sup>16</sup> - 2 = 65534
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Band Offset: `min(max(16, 65536/16), 256)` = `min(4096, 256)` = 256
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Static band start: 10.96.0.1
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Static band ends: 10.96.1.0
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Range end: 10.96.255.254
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{{< mermaid >}}
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pie showData
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title 10.96.0.0/16
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"Static" : 256
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"Dynamic" : 65278
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{{< /mermaid >}}
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-->
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范围大小：2<sup>16</sup> - 2 = 65534
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带宽偏移量：`min(max(16, 65536/16), 256)` = `min(4096, 256)` = 256
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静态带宽起始地址：10.96.0.1
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静态带宽结束地址：10.96.1.0
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范围结束地址：10.96.255.254
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{{< mermaid >}}
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pie showData
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title 10.96.0.0/16
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"静态分配" : 256
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"动态分配" : 65278
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{{< /mermaid >}}
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<!--
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## {{% heading "whatsnext" %}}
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* Read about [Service External Traffic Policy](/docs/tasks/access-application-cluster/create-external-load-balancer/#preserving-the-client-source-ip)
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* Read about [Connecting Applications with Services](/docs/concepts/services-networking/connect-applications-service/)
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* Read about [Services](/docs/concepts/services-networking/service/)
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-->
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## {{% heading "whatsnext" %}}
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* 阅读[服务外部流量策略](/zh-cn/docs/tasks/access-application-cluster/create-external-load-balancer/#preserving-the-client-source-ip)
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* 阅读[应用程序与服务连接](/zh-cn/docs/concepts/services-networking/connect-applications-service/)
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* 阅读[服务](/zh-cn/docs/concepts/services-networking/service/)
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