toleration / ping-service

learning/faq/ping-service.md

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+---
+vssueId: 173
+layout: LearningLayout
+description: Kubernetes教程_本文解释了Kubernetes中为什么ping Service 不能成功的原因
+meta:
+  - name: keywords
+    content: Kubernetes教程,K8S教程,Kubernetes Service
+---
+
+# 为什么Kubernetes Service不能ping
+
+<AdSenseTitle>
+
+</AdSenseTitle>
+
+## 现象
+
+**Kubernetes Service 不能 ping**
+
+例如对于 [example](/guide/example/import.html) 中的 Service `gateway-example`，可以执行 `nslookup` 命令，如下所示：
+
+``` 
+[root@gateway-example-6f6f45cd6-px8bn eip]# nslookup gateway-example
+Server:         10.96.0.10
+Address:        10.96.0.10#53
+
+Name:   gateway-example.example.svc.cluster.local
+Address: 10.105.141.232
+```
+
+但是执行 `ping` 命令则会失败：
+
+``` 
+[root@gateway-example-6f6f45cd6-px8bn eip]# ping gateway-example
+PING gateway-example.example.svc.cluster.local (10.105.141.232) 56(84) bytes of data.
+From 172.17.76.171 (172.17.76.171) icmp_seq=1 Time to live exceeded
+From 172.17.76.171 (172.17.76.171) icmp_seq=2 Time to live exceeded
+From 172.17.76.171 (172.17.76.171) icmp_seq=3 Time to live exceeded
+From 172.17.76.171 (172.17.76.171) icmp_seq=4 Time to live exceeded
+^C
+--- gateway-example.example.svc.cluster.local ping statistics ---
+4 packets transmitted, 0 received, +4 errors, 100% packet loss, time 3003ms
+```
+
+执行 `curl` 命令会成功：(如果后端 Pod 正常)
+
+```
+[root@gateway-example-6f6f45cd6-px8bn eip]# curl gateway-example:9201
+{"timestamp":"2019-11-29T15:29:39.515+0000","path":"/","status":404,"error":"Not Found","message":null}
+```
+
+执行 `telnet` 命令也可以成功：(如果后端 Pod 正常)
+
+```
+[root@gateway-example-6f6f45cd6-px8bn eip]# telnet gateway-example 9201
+Trying 10.105.141.232...
+Connected to gateway-example.
+Escape character is '^]'.
+```
+
+## 解释
+
+在 Kubernetes 的网络中，Service 就是 ping 不通的。因为 Kubernetes 只是为 Service 生成了一个虚拟 IP 地址，实现的方式有：
+* [User space 代理模式](/learning/k8s-intermediate/service/service-details.html#user-space-代理模式)
+* [Iptables 代理模式](/learning/k8s-intermediate/service/service-details.html#iptables-代理模式)
+* [IPVS 代理模式](/learning/k8s-intermediate/service/service-details.html#ipvs-代理模式)
+
+不管是哪种代理模式，Kubernetes Service 的 IP 背后都没有任何实体可以响应「ICMP」，全称为 Internet 控制报文协议（Internet Control Message Protocol）。参考 [每天都在用的Ping命令，它到底是什么？](https://www.jianshu.com/p/dc9de5038874)
+
+通过 Service 访问 Pod 时的数据传递方式，可参考 [数据包的传递：Service-to-Pod](/learning/k8s-intermediate/service/network.html#数据包的传递：service-to-pod)