跨节点通讯，需要通过NAT，即需要做源地址转换。
k8s网络通信：
1） 容器间通信：同一个pod内的多个容器间的通信，通过lo即可实现；
2） pod之间的通信，pod ip <---> pod ip，pod和pod之间要不经过任何转换即可通信；
3） pod和service通信:pod ip <----> cluster ip（即service ip）<---->pod ip，他们通过iptables或ipvs实现通信，另外大家要注意ipvs取代不了iptables，因为ipvs只能做负载均衡，而做不了nat转换；
4） Service与集群外部客户端的通信
[root@master pki]# kubectl get configmap -n kube-system NAME DATA AGE coredns 1 22d extension-apiserver-authentication 6 22d kube-flannel-cfg 2 22d kube-proxy 2 22d kubeadm-config 1 22d kubelet-config-1.11 1 22d kubernetes-dashboard-settings 1 9h
[root@master pki]# kubectl get configmap kube-proxy -o yaml -n kube-system mode: ""
看到mode是空的，我们把它改为ipvs就可以了。
k8s要靠CNI接口接入其他插件来实现网络通讯。目前比较流行的插件有flannet，callco，canel，kube-router。
这些插件使用的解决方案都如下：
1）虚拟网桥，虚拟网卡，多个容器共用一个虚拟网卡进行通信；
2）多路复用：MacVLAN，多个容器共用一个物理网卡进行通信；
3）硬件交换：SR-LOV，一个物理网卡可以虚拟出多个接口，这个性能最好。
CNI插件存放位置
[root@master ~]# cat /etc/cni/net.d/10-flannel.conflist
{
"name": "cbr0",
"plugins": [
{
"type": "flannel",
"delegate": {
"hairpinMode": true,
"isDefaultGateway": true
}
},
{
"type": "portmap",
"capabilities": {
"portMappings": true
}
}
]
}
flanel只支持网络通讯，但是不支持网络策略。
callco网络通讯和网络策略都支持。
canel：flanel+callco合起来的功能。
我们可以部署flanel提供网络通讯，再部署一个callco只提供网络策略。而不用canel。
mtu：是指一种通信协议的某一层上面所能通过的最大数据包大小。
[root@master ~]# ifconfig
cni0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1450
inet 10.244.0.1 netmask 255.255.255.0 broadcast 0.0.0.0
inet6 fe80::4097:d5ff:fe28:6b64 prefixlen 64 scopeid 0x20<link>
ether 0a:58:0a:f4:00:01 txqueuelen 1000 (Ethernet)
RX packets 1609844 bytes 116093191 (110.7 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 1632952 bytes 577989701 (551.2 MiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
docker0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
inet 172.17.0.1 netmask 255.255.0.0 broadcast 172.17.255.255
ether 02:42:83:f8:b8:ff txqueuelen 0 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
ens192: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 172.16.1.100 netmask 255.255.255.0 broadcast 172.16.1.255
inet6 fe80::9cf3:d9de:59f:c320 prefixlen 64 scopeid 0x20<link>
inet6 fe80::5707:6115:267b:bff5 prefixlen 64 scopeid 0x20<link>
inet6 fe80::e34:f952:2859:4c69 prefixlen 64 scopeid 0x20<link>
ether 00:50:56:a2:4e:cb txqueuelen 1000 (Ethernet)
RX packets 5250378 bytes 704067861 (671.4 MiB)
RX errors 139 dropped 190 overruns 0 frame 0
TX packets 4988169 bytes 4151179300 (3.8 GiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
flannel.1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1450
inet 10.244.0.0 netmask 255.255.255.255 broadcast 0.0.0.0
inet6 fe80::a82c:bcff:fef8:895c prefixlen 64 scopeid 0x20<link>
ether aa:2c:bc:f8:89:5c txqueuelen 0 (Ethernet)
RX packets 51 bytes 3491 (3.4 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 53 bytes 5378 (5.2 KiB)
TX errors 0 dropped 10 overruns 0 carrier 0 collisions 0
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10<host>
loop txqueuelen 1 (Local Loopback)
RX packets 59118846 bytes 15473986573 (14.4 GiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 59118846 bytes 15473986573 (14.4 GiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
veth6ec94aab: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1450
inet6 fe80::487d:5bff:fef7:484d prefixlen 64 scopeid 0x20<link>
ether 4a:7d:5b:f7:48:4d txqueuelen 0 (Ethernet)
RX packets 88112 bytes 19831802 (18.9 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 105718 bytes 13343894 (12.7 MiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
vethf703483a: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1450
inet6 fe80::b06a:eaff:fec3:33a8 prefixlen 64 scopeid 0x20<link>
ether b2:6a:ea:c3:33:a8 txqueuelen 0 (Ethernet)
RX packets 760882 bytes 59400960 (56.6 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 763263 bytes 282299805 (269.2 MiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
vethff579703: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1450
inet6 fe80::d82f:37ff:fe9a:b6d0 prefixlen 64 scopeid 0x20<link>
ether da:2f:37:9a:b6:d0 txqueuelen 0 (Ethernet)
RX packets 760850 bytes 59398245 (56.6 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 764016 bytes 282349248 (269.2 MiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
通过ifconfig命令，我们可以看到flannel.1的地址是10.244.0.0，子网掩码是255.255.255.255，mtu是1450，mtu要留出一部分做封装叠加，额外开销使用。
cni0只有在pod运行时才会出现。
两个节点上的pod可以借助flannel隧道进行通信。默认使用的VxLAN协议，因为它有额外开销，所以性能有点低。
flannel第二种协议叫host-gw(host gateway)，即Node节点把自己的网络接口当做pod的网关使用，从而使不同节点上的node进行通信，这个性能比VxLAN高，因为它没有额外开销。不过他有个缺点， 就是各node节点必须在同一个网段中 。
另外，如果两 个pod所在节点在同一个网段中 ，可以让VxLAN也支持host-gw的功能， 即直接通过物理网卡的网关路由转发，而不用隧道flannel叠加，从而提高了VxLAN的性能，这种flannel的功能叫directrouting。
[root@master ~]# kubectl get daemonset -n kube-system NAME DESIRED CURRENT READY UP-TO-DATE AVAILABLE NODE SELECTOR AGE kube-flannel-ds-amd64 3 3 3 3 3 beta.kubernetes.io/arch=amd64
[root@master ~]# kubectl get pods -n kube-system -o wide NAME READY STATUS RESTARTS AGE IP NODE kube-flannel-ds-amd64-6zqzr 1/1 Running 8 22d 172.16.1.100 master kube-flannel-ds-amd64-7qtcl 1/1 Running 7 22d 172.16.1.101 node1 kube-flannel-ds-amd64-kpctn 1/1 Running 6 22d 172.16.1.102 node2
看到flannel是以pod的daemonset控制器形式运行的（其实flannel还可以以守护进程的方式运行）。
[root@master ~]# kubectl get configmap -n kube-system NAME DATA AGE kube-flannel-cfg 2 22d
[root@master ~]#kubectl get configmap -n kube-system kube-flannel-cfg -o json -n kube-system
\\\"10.244.0.0/16\\\",\\n \\\"Backend\\\": {\\n \\\"Type\\\": \\\"vxlan\
flannel的配置参数：
1、network ：flannel使用的CIDR格式的网络地址，用于为pod配置网络功能。
1)10.244.0.0/16--->
master: 10.244.0.0./24
node01: 10.244.1.0/24
....
node255: 10.244.255.0/24
可以支持255个节点
2)10.0.0.0/8
10.0.0.0/24
...
10.255.255.0/24
可以支持6万多个节点
2、SubnetLen ：把network切分为子网供各节点使用时，使用多长的掩码进行切分，默认为24位；
3、SubnetMin ：指明子网中的地址段最小多少可以分给子网使用，比如可以限制10.244.10.0/24，这样0~9就不让用；
4、SubnetMax ：表示最多使用多少个，比如10.244.100.0/24
5、Backend: Vxlan，host-gw，udp（最慢）
flannel
支持多种后端
Vxlan
1.valan
2.Dirextrouting
host-gw：Host Gateway #不推荐，只能在二层网络中，不支持跨网络，如果有成千上万的Pod，容易产生广播风暴
UDP：性能差
[root@master ~]# kubectl get pods -o wide NAME READY STATUS RESTARTS AGE IP NODE myapp-deploy-69b47bc96d-79fqh 1/1 Running 4 7d 10.244.1.97 node1 myapp-deploy-69b47bc96d-tc54k 1/1 Running 4 7d 10.244.2.88 node2
[root@master ~]# kubectl exec -it myapp-deploy-69b47bc96d-79fqh -- /bin/sh / # ping 10.244.2.88 #ping对方Node上容器的ip PING 10.244.2.88 (10.244.2.88): 56 data bytes 64 bytes from 10.244.2.88: seq=0 ttl=62 time=0.459 ms 64 bytes from 10.244.2.88: seq=0 ttl=62 time=0.377 ms 64 bytes from 10.244.2.88: seq=1 ttl=62 time=0.252 ms 64 bytes from 10.244.2.88: seq=2 ttl=62 time=0.261 ms
在其他节点上抓包，发现在ens192上抓不到包。所以没走ens192
[root@master ~]# tcpdump -i ens192 -nn icmp
[root@master ~]# yum install bridge-utils -y
[root@master ~]# brctl show docker0 bridge namebridge idSTP enabledinterfaces docker08000.024283f8b8ffno
[root@master ~]# brctl show cni0 bridge namebridge idSTP enabledinterfaces cni08000.0a580af40001noveth6ec94aab vethf703483a vethff579703
可以看到veth这些接口都是桥接到cni0上的。
brctl show表示查看已有网桥。
[root@node1 ~]# tcpdump -i cni0 -nn icmp tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on cni0, link-type EN10MB (Ethernet), capture size 262144 bytes 23:40:11.370754 IP 10.244.1.97 > 10.244.2.88: ICMP echo request, id 4864, seq 96, length 64 23:40:11.370988 IP 10.244.2.88 > 10.244.1.97: ICMP echo reply, id 4864, seq 96, length 64 23:40:12.370888 IP 10.244.1.97 > 10.244.2.88: ICMP echo request, id 4864, seq 97, length 64 23:40:12.371090 IP 10.244.2.88 > 10.244.1.97: ICMP echo reply, id 4864, seq 97, length 64 ^X23:40:13.371015 IP 10.244.1.97 > 10.244.2.88: ICMP echo request, id 4864, seq 98, length 64 23:40:13.371239 IP 10.244.2.88 > 10.244.1.97: ICMP echo reply, id 4864, seq 98, length 64 23:40:14.371128 IP 10.244.1.97 > 10.244.2.88: ICMP echo request, id 4864, seq 99, length 64
可以看到，在node节点，可以在cni0端口上抓到容器里面的Ping时的包。
其实，上面ping时的数据流是先从cni0进来，然后从flannel.1出去，最后借助物理网卡ens32发出去。所以，我们在flannel.1上也能抓到包：
[root@node1 ~]# tcpdump -i flannel.1 -nn icmp tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on flannel.1, link-type EN10MB (Ethernet), capture size 262144 bytes 03:12:36.823315 IP 10.244.1.97 > 10.244.2.88: ICMP echo request, id 4864, seq 12840, length 64 03:12:36.823496 IP 10.244.2.88 > 10.244.1.97: ICMP echo reply, id 4864, seq 12840, length 64 03:12:37.823490 IP 10.244.1.97 > 10.244.2.88: ICMP echo request, id 4864, seq 12841, length 64 03:12:37.823634 IP 10.244.2.88 > 10.244.1.97: ICMP echo reply, id 4864, seq 12841, length 64
同样，在ens192物理网卡上也能抓到包：
[root@node1 ~]# tcpdump -i ens192 -nn host 172.16.1.102 #172.16.1.102是node2的物理ip tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on ens192, link-type EN10MB (Ethernet), capture size 262144 bytes 10:59:24.234174 IP 172.16.1.101.60617 > 172.16.1.102.8472: OTV, flags [I] (0x08), overlay 0, instance 1 IP 10.244.1.97 > 10.244.2.88: ICMP echo request, id 7168, seq 0, length 64 10:59:24.234434 IP 172.16.1.102.54894 > 172.16.1.101.8472: OTV, flags [I] (0x08), overlay 0, instance 1 IP 10.244.2.88 > 10.244.1.97: ICMP echo reply, id 7168, seq 0, length 64 10:59:25.234301 IP 172.16.1.101.60617 > 172.16.1.102.8472: OTV, flags [I] (0x08), overlay 0, instance 1 IP 10.244.1.97 > 10.244.2.88: ICMP echo request, id 7168, seq 1, length 64 10:59:25.234469 IP 172.16.1.102.54894 > 172.16.1.101.8472: OTV, flags [I] (0x08), overlay 0, instance 1 IP 10.244.2.88 > 10.244.1.97: ICMP echo reply, id 7168, seq 1, length 64 10:59:26.234415 IP 172.16.1.101.60617 > 172.16.1.102.8472: OTV, flags [I] (0x08), overlay 0, instance 1 IP 10.244.1.97 > 10.244.2.88: ICMP echo request, id 7168, seq 2, length 64 10:59:26.234592 IP 172.16.1.102.54894 > 172.16.1.101.8472: OTV, flags [I] (0x08), overlay 0, instance 1 IP 10.244.2.88 > 10.244.1.97: ICMP echo reply, id 7168, seq 2, length 64 10:59:27.234528 IP 172.16.1.101.60617 > 172.16.1.102.8472: OTV, flags [I] (0x08), overlay 0, instance 1 IP 10.244.1.97 > 10.244.2.88: ICMP echo request, id 7168, seq 3, length 64
下面我们把flannel的通信模式改成directrouting的方式 ，从Git上下载配置文件，重新删除网络在重新应用，这个步骤不推荐。但是视频就这么做的。作者是修改源文件，然后重启了k8s集群，他的这个方式造成pod后续创建的都处于pendding状态。
https://github.com/coreos/flannel
wget https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml
找到
"Network": "10.244.0.0/16",
"Backend": {
"Type": "vxlan",
"Directrouting": true //新增这一行。上面记得加逗号
先删除之前的flannel，生产环境不要这么干
[root@master flannel]# kubectl delete -f kube-flannel.yml
创建新的
[root@master flannel]# kubectl get pods -n kube-system
[root@master flannel]# kubectl get configmap kube-flannel-cfg -o json -n kube-system
"net-conf.json": "{\n \"Network\": \"10.244.0.0/16\",\n \"Backend\": {\n \"Type\": \"vxlan\",\n \"Directrouting\": true\n }\n}\n"
看到有Directrouting，说明生效了。
[root@master ~]# ip route show default via 172.16.1.254 dev ens192 proto static metric 100 10.244.0.0/24 dev cni0 proto kernel scope link src 10.244.0.1 #访问本机直接在本机直接转发，而不需要其他接口，这就是directrouting 10.244.1.0/24 via 172.16.1.101 dev ens192 #看到现在访问10.244.1.0，通过本地物理网卡ens192上的172.16.1.101送出去，即通过物理网卡通信了，而不再通过隧道flannel通信。 10.244.2.0/24 via 172.16.1.102 dev ens192 172.16.1.0/24 dev ens192 proto kernel scope link src 172.16.1.100 metric 100 172.17.0.0/16 dev docker0 proto kernel scope link src 172.17.0.1
继续登录到一个pod中进行ping测试：
[root@master ~]# kubectl get pods -o wide NAME READY STATUS RESTARTS AGE IP NODE myapp-deploy-69b47bc96d-75g2b 1/1 Running 0 12m 10.244.1.124 node1 myapp-deploy-69b47bc96d-jwgwm 1/1 Running 0 3s 10.244.2.100 node2
[root@master ~]# kubectl exec -it myapp-deploy-69b47bc96d-75g2b -- /bin/sh / # ping 10.244.2.100 PING 10.244.2.100 (10.244.2.100): 56 data bytes 64 bytes from 10.244.2.100: seq=0 ttl=62 time=0.536 ms 64 bytes from 10.244.2.100: seq=1 ttl=62 time=0.206 ms 64 bytes from 10.244.2.100: seq=2 ttl=62 time=0.206 ms 64 bytes from 10.244.2.100: seq=3 ttl=62 time=0.203 ms 64 bytes from 10.244.2.100: seq=4 ttl=62 time=0.210 ms
[root@node1 ~]# tcpdump -i ens192 -nn icmp tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on ens192, link-type EN10MB (Ethernet), capture size 262144 bytes 12:31:10.899403 IP 10.244.1.124 > 10.244.2.100: ICMP echo request, id 8960, seq 24, length 64 12:31:10.899546 IP 10.244.2.100 > 10.244.1.124: ICMP echo reply, id 8960, seq 24, length 64 12:31:11.899505 IP 10.244.1.124 > 10.244.2.100: ICMP echo request, id 8960, seq 25, length 64 12:31:11.899639 IP 10.244.2.100 > 10.244.1.124: ICMP echo reply, id 8960, seq 25, length 64
通过抓包可以看到，现在在pod中进行互ping，是从物理网卡ens192进出的，这就是directrouting，这种性能比默认vxlan高。
[root@node
1
~]# tcpdump -i cni
0
-nn icmp
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on cni
0
, link-type EN
10
MB (Ethernet), capture size
262144
bytes
23:
40:
11.370754
IP
10.244
.
1.97
>
10.244
.
2.88:
ICMP echo request, id
4864
, seq
96
, length
64
23:
40:
11.370988
IP
10.244
.
2.88
>
10.244
.
1.97:
ICMP echo reply, id
4864
, seq
96
, length
64
23:
40:
12.370888
IP
10.244
.
1.97
>
10.244
.
2.88:
ICMP echo request, id
4864
, seq
97
, length
64
23:
40:
12.371090
IP
10.244
.
2.88
>
10.244
.
1.97:
ICMP echo reply, id
4864
, seq
97
, length
64
^X
23:
40:
13.371015
IP
10.244
.
1.97
>
10.244
.
2.88:
ICMP echo request, id
4864
, seq
98
, length
64
23:
40:
13.371239
IP
10.244
.
2.88
>
10.244
.
1.97:
ICMP echo reply, id
4864
, seq
98
, length
64
23:
40:
14.371128
IP
10.244
.
1.97
>
10.244
.
2.88:
ICMP echo request, id
4864
, seq
99
, length
64