---
title: "服务、负载均衡和联网"
weight: 60
description: Kubernetes 网络背后的概念和资源。
---

<!--
## The Kubernetes network model

Every [`Pod`](/docs/concepts/workloads/pods/) gets its own IP address.
This means you do not need to explicitly create links between `Pods` and you
almost never need to deal with mapping container ports to host ports.  
This creates a clean, backwards-compatible model where `Pods` can be treated
much like VMs or physical hosts from the perspectives of port allocation,
naming, service discovery, [load balancing](/docs/concepts/services-networking/ingress/#load-balancing), application configuration,
and migration.

Kubernetes imposes the following fundamental requirements on any networking
implementation (barring any intentional network segmentation policies):

* pods on a [node](/docs/concepts/architecture/nodes/) can communicate with all pods on all nodes without NAT
* agents on a node (e.g. system daemons, kubelet) can communicate with all
  pods on that node

Note: For those platforms that support `Pods` running in the host network (e.g.
Linux):

* pods in the host network of a node can communicate with all pods on all
  nodes without NAT
-->
## Kubernetes 网络模型   {#the-kubernetes-network-model}

每一个 [`Pod`](/zh/docs/concepts/workloads/pods/) 都有它自己的IP地址，
这就意味着你不需要显式地在 `Pod` 之间创建链接， 你几乎不需要处理容器端口到主机端口之间的映射。
这将形成一个干净的、向后兼容的模型；在这个模型里，从端口分配、命名、服务发现、
[负载均衡](/zh/docs/concepts/services-networking/ingress/#load-balancing)、应用配置和迁移的角度来看，
`Pod` 可以被视作虚拟机或者物理主机。

Kubernetes 强制要求所有网络设施都满足以下基本要求（从而排除了有意隔离网络的策略）：

* [节点](/zh/docs/concepts/architecture/nodes/)上的 Pod 可以不通过 NAT 和其他任何节点上的 Pod 通信
* 节点上的代理（比如：系统守护进程、kubelet）可以和节点上的所有 Pod 通信

备注：对于支持在主机网络中运行 `Pod` 的平台（比如：Linux）：

* 运行在节点主机网络里的 Pod 可以不通过 NAT 和所有节点上的 Pod 通信

<!--
This model is not only less complex overall, but it is principally compatible
with the desire for Kubernetes to enable low-friction porting of apps from VMs
to containers.  If your job previously ran in a VM, your VM had an IP and could
talk to other VMs in your project.  This is the same basic model.

Kubernetes IP addresses exist at the `Pod` scope - containers within a `Pod`
share their network namespaces - including their IP address and MAC address.
This means that containers within a `Pod` can all reach each other's ports on
`localhost`. This also means that containers within a `Pod` must coordinate port
usage, but this is no different from processes in a VM.  This is called the
"IP-per-pod" model.
-->
这个模型不仅不复杂，而且还和 Kubernetes 的实现从虚拟机向容器平滑迁移的初衷相符，
如果你的任务开始是在虚拟机中运行的，你的虚拟机有一个 IP，
可以和项目中其他虚拟机通信。这里的模型是基本相同的。

Kubernetes 的 IP 地址存在于 `Pod` 范围内 - 容器共享它们的网络命名空间 - 包括它们的 IP 地址和 MAC 地址。
这就意味着 `Pod` 内的容器都可以通过 `localhost` 到达对方端口。
这也意味着 `Pod` 内的容器需要相互协调端口的使用，但是这和虚拟机中的进程似乎没有什么不同，
这也被称为“一个 Pod 一个 IP”模型。

<!--
How this is implemented is a detail of the particular container runtime in use.

It is possible to request ports on the `Node` itself which forward to your `Pod`
(called host ports), but this is a very niche operation. How that forwarding is
implemented is also a detail of the container runtime. The `Pod` itself is
blind to the existence or non-existence of host ports.
-->
如何实现以上需求是所使用的特定容器运行时的细节。

也可以在 `Node` 本身请求端口，并用这类端口转发到你的 `Pod`（称之为主机端口），
但这是一个很特殊的操作。转发方式如何实现也是容器运行时的细节。
`Pod` 自己并不知道这些主机端口的存在。

<!--
Kubernetes networking addresses four concerns:
- Containers within a Pod [use networking to communicate](/docs/concepts/services-networking/dns-pod-service/) via loopback.
- Cluster networking provides communication between different Pods.
- The [Service resource](/docs/concepts/services-networking/service/) lets you [expose an application running in Pods](/docs/concepts/services-networking/connect-applications-service/) to be reachable from outside your cluster.
- You can also use Services to [publish services only for consumption inside your cluster](/docs/concepts/services-networking/service-traffic-policy/).
-->

Kubernetes 网络解决四方面的问题：
- 一个 Pod 中的容器之间[通过本地回路（loopback）通信](/zh/docs/concepts/services-networking/dns-pod-service/)。
- 集群网络在不同 pod 之间提供通信。
- [Service 资源](/zh/docs/concepts/services-networking/service/)允许你
  [对外暴露 Pods 中运行的应用程序](/zh/docs/concepts/services-networking/connect-applications-service/)，
  以支持来自于集群外部的访问。
- 可以使用 Services 来[发布仅供集群内部使用的服务](/zh/docs/concepts/services-networking/service-traffic-policy/)。