[zh] Sync concepts section (6)
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Qiming Teng
@@ -3,12 +3,23 @@ title: Pod 与 Service 的 DNS
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content_type: concept
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weight: 20
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---
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<!--
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reviewers:
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- davidopp
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- thockin
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title: DNS for Services and Pods
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content_type: concept
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weight: 20
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-->
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<!-- overview -->
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<!--
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This page provides an overview of DNS support by Kubernetes.
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Kubernetes creates DNS records for services and pods. You can contact
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services with consistent DNS names instead of IP addresses.
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-->
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本页面提供 Kubernetes 对 DNS 的支持的概述。
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Kubernetes 为服务和 Pods 创建 DNS 记录。
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你可以使用一致的 DNS 名称而非 IP 地址来访问服务。
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<!-- body -->
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@@ -21,40 +32,93 @@ resolve DNS names.
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-->
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## 介绍
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Kubernetes DNS 在群集上调度 DNS Pod 和服务，并配置 kubelet 以告知各个容器使用 DNS 服务的 IP 来解析 DNS 名称。
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Kubernetes DNS 在集群上调度 DNS Pod 和服务，并配置 kubelet 以告知各个容器
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使用 DNS 服务的 IP 来解析 DNS 名称。
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<!--
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### What things get DNS names?
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Every Service defined in the cluster (including the DNS server itself) is
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assigned a DNS name. By default, a client Pod's DNS search list will
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include the Pod's own namespace and the cluster's default domain. This is best
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illustrated by example:
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assigned a DNS name. By default, a client Pod's DNS search list includes the
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Pod's own namespace and the cluster's default domain.
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-->
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集群中定义的每个 Service （包括 DNS 服务器自身）都被赋予一个 DNS 名称。
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默认情况下，客户端 Pod 的 DNS 搜索列表会包含 Pod 自身的名字空间和集群
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的默认域。
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Assume a Service named `foo` in the Kubernetes namespace `bar`. A Pod running
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in namespace `bar` can look up this service by simply doing a DNS query for
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`foo`. A Pod running in namespace `quux` can look up this service by doing a
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DNS query for `foo.bar`.
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<!--
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### Namespaces of Services
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The following sections detail the supported record types and layout that is
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A DNS query may return different results based on the namespace of the pod making
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it. DNS queries that don't specify a namespace are limited to the pod's
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namespace. Access services in other namespaces by specifying it in the DNS query.
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For example, consider a pod in a `test` namespace. A `data` service is in
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the `prod` namespace.
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A query for `data` returns no results, because it uses the pod's `test` namespace.
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A query for `data.prod` returns the intended result, because it specifies the
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namespace.
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-->
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### Service 的名字空间
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DNS 查询可能因为执行查询的 Pod 所在的名字空间而返回不同的结果。
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不指定名字空间的 DNS 查询会被限制在 Pod 所在的名字空间内。
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要访问其他名字空间中的服务，需要在 DNS 查询中给出名字空间。
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例如，假定名字空间 `test` 中存在一个 Pod，`prod` 名字空间中存在一个服务
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`data`。
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Pod 查询 `data` 时没有返回结果，因为使用的是 Pod 的名字空间 `test`。
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Pod 查询 `data.prod` 时则会返回预期的结果，因为查询中指定了名字空间。
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<!--
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DNS queries may be expanded using the pod's `/etc/resolv.conf`. Kubelet
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sets this file for each pod. For example, a query for just `data` may be
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expanded to `data.test.cluster.local`. The values of the `search` option
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are used to expand queries. To learn more about DNS queries, see
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[the `resolv.conf` manual page.](https://www.man7.org/linux/man-pages/man5/resolv.conf.5.html)
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-->
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DNS 查询可以使用 Pod 中的 `/etc/resolv.conf` 展开。kubelet 会为每个 Pod
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生成此文件。例如，对 `data` 的查询可能被展开为 `data.test.cluster.local`。
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`search` 选项的取值会被用来展开查询。要进一步了解 DNS 查询，可参阅
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[`resolv.conf` 手册页面](https://www.man7.org/linux/man-pages/man5/resolv.conf.5.html)。
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```
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nameserver 10.32.0.10
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search <namespace>.svc.cluster.local svc.cluster.local cluster.local
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options ndots:5
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```
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<!--
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In summary, a pod in the _test_ namespace can successfully resolve either
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`data.prod` or `data.prod.cluster.local`.
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-->
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概括起来，名字空间 `test` 中的 Pod 可以成功地解析 `data.prod` 或者
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`data.prod.cluster.local`。
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<!--
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### DNS Records
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What objects get DNS records?
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-->
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### DNS 记录 {#dns-records}
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哪些对象会获得 DNS 记录呢？
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1. Services
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2. Pods
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<!--
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The following sections detail the supported DNS record types and layout that is
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supported. Any other layout or names or queries that happen to work are
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considered implementation details and are subject to change without warning.
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For more up-to-date specification, see
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[Kubernetes DNS-Based Service Discovery](https://github.com/kubernetes/dns/blob/master/docs/specification.md).
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-->
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## 哪些对象会有 DNS 名字? {#what-things-get-dns-names}
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在集群中定义的每个 Service（包括 DNS 服务器自身）都会被指派一个 DNS 名称。
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默认，一个客户端 Pod 的 DNS 搜索列表将包含该 Pod 自己的名字空间和集群默认域。
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如下示例是一个很好的说明：
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假设在 Kubernetes 集群的名字空间 `bar` 中，定义了一个服务 `foo`。
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运行在名字空间 `bar` 中的 Pod 可以简单地通过 DNS 查询 `foo` 来找到该服务。
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运行在名字空间 `quux` 中的 Pod 可以通过 DNS 查询 `foo.bar` 找到该服务。
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以下各节详细介绍了受支持的记录类型和支持的布局。
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以下各节详细介绍了被支持的 DNS 记录类型和被支持的布局。
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其它布局、名称或者查询即使碰巧可以工作，也应视为实现细节，
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将来很可能被更改而且不会因此出现警告。
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将来很可能被更改而且不会因此发出警告。
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有关最新规范请查看
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[Kubernetes 基于 DNS 的服务发现](https://github.com/kubernetes/dns/blob/master/docs/specification.md)。
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@@ -301,7 +365,7 @@ If a Pod enables this feature and its FQDN is longer than 64 character, it will
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如果 Pod 启用这一特性，而其 FQDN 超出 64 字符，Pod 的启动会失败。
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Pod 会一直出于 `Pending` 状态（通过 `kubectl` 所看到的 `ContainerCreating`），
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并产生错误事件，例如
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并产生错误事件，例如
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"Failed to construct FQDN from pod hostname and cluster domain, FQDN
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`long-FQDN` is too long (64 characters is the max, 70 characters requested)."
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（无法基于 Pod 主机名和集群域名构造 FQDN，FQDN `long-FQDN` 过长，至多 64
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