目录
1. 背景
最近在看Swarm，梳理了了一遍Swarm集群负载均衡的实现方式，记录如下
2. 参考
3. 环境
centos 7.9
docker Swarm
4. 概念
在Swarm中，通IPVS和VXLAN技术和实现服务负载均衡，其中IPVS负责根据FWM（firewall mark）取代VIP进行数据包的负载均衡，VXLAN负责组建跨主机之间的ingress网络通讯。
5. Swarm 网络
5.1 Swarm 网络连接情况
先看以下Swarm集群示例。
上图同一节点内 和 两个节点之间网络连接的情况，详述如下：
- 两个节点分别是Centos7-10和Centos7-18两台宿主机
- 橙色连线表示宿主机之间的物理网络连接
- 蓝色连线表示在宿主机内默认命名空间docker_gwbridge网络连接，它连接了ingress和容器。docker_gwbridge负责外部访问集群服务和容器直接访问外部的网络通讯。
- 浅绿色连线表示ingress网络的连接，它通过vxlan跨主机组网，同时将本节点容器接入网络。
- 粉色连线表示自定义Overlay网络，原理与ingress相同
- 在一台宿主机中除默认命名空间外，还有3个命名空间，以宿主机Centos7-10为例，它们的作用是：
6.1) 命名空间：ingress_sbox（id: 1）是ingress网络入口，负责IPVS负载均衡
6.2) 命名空间：1-9j40lm9s5d (id: 0) 负责ingress通过vxlan跨主机组网，同时连接ingress入口和本节点容器
6.3) 命名空间：a567c55696f4 (id: 4) 是节点centos7-10上容器的命名空间，连接ingress网络，如果存在多个容器，就会有多个容器命名空间。同样，7fd6d0335ad4 (id: 4) 是节点centos7-18上容器的命名空间
5.2 外部访问数据包转发流程
6 Swarm集群服务信息
Swarm集群和服务已提前创建完成，具体信息如下：
- Swarm集群3个节点
- centos7-10： IP 10.211.55.10，管理节点
- centos7-18： IP 10.211.55.18，从节点
- centos7-22： IP 10.211.55.22，从节点
[root@centos7-10 ~]# docker node ls
ID HOSTNAME STATUS AVAILABILITY MANAGER STATUS ENGINE VERSION
w92t66jii4jflz1vb0kotr0df * centos7-10.localdomain Ready Active Leader 24.0.7
9p6kone8vdwkdne55svrj6k5n centos7-18.localdomain Ready Active 24.0.7
x5y16qjbxuxv322to4hbiymik centos7-22.localdomain Ready Active 24.0.7
- Swarm集群运行网络
- ingress 集群自动创建的管理网络
- docker_gwbridge 集群自动创建的本地网络
- ol_network 自定义创建的Overlay网络（不在本文讨论内容，可忽略）
[root@centos7-10 ~]# docker network ls
NETWORK ID NAME DRIVER SCOPE
e384cf8f2e42 bridge bridge local
333348eb8ff4 docker_gwbridge bridge local
65a57293726b host host local
9j40lm9s5dte ingress overlay swarm
2db17c1087bf none null local
9u6c1vlfy4kv ol_network overlay swarm
- ingress 网络详情
- Overlay网络
- IP 10.0.0.0/24，网关 10.0.0.1
[root@centos7-10 ~]# docker network inspect ingress
[
{
"Name": "ingress",
"Id": "9j40lm9s5dtedg04r6jywqr1k",
"Created": "2024-03-05T14:40:26.202301824+08:00",
"Scope": "swarm",
"Driver": "overlay",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": [
{
"Subnet": "10.0.0.0/24",
"Gateway": "10.0.0.1"
}
]
},
"Internal": false,
"Attachable": false,
"Ingress": true,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": false,
"Containers": {
"8593fe83b9259ace2cf6c1f0718c48c9206da0a657759676f7599014120d48e0": {
"Name": "my-nginx.3.s754p61l6729e117si904236b",
"EndpointID": "2425b820ba06cbb53bb5f329f87d6013874968c77ebbe0a4f1e38b0756097242",
"MacAddress": "02:42:0a:00:00:10",
"IPv4Address": "10.0.0.16/24",
"IPv6Address": ""
},
"86e2f87808941e12b5912ec5ee922dc48b04fbb4ce035189323eda51d4b74cac": {
"Name": "my-nginx.1.q3gjmacbb0k0ay2ehi1uvz7dw",
"EndpointID": "660df37adc3404a3bbeaf7cd9c979710bd49f100176e5185bfa0d861059c84e1",
"MacAddress": "02:42:0a:00:00:11",
"IPv4Address": "10.0.0.17/24",
"IPv6Address": ""
},
"ingress-sbox": {
"Name": "ingress-endpoint",
"EndpointID": "a4139caa54328f05f0a06ca8e0f7218fa8209fb09553c67f4dd073372eaffd33",
"MacAddress": "02:42:0a:00:00:02",
"IPv4Address": "10.0.0.2/24",
"IPv6Address": ""
}
},
"Options": {
"com.docker.network.driver.overlay.vxlanid_list": "4096"
},
"Labels": {},
"Peers": [
{
"Name": "ec5d0b20deba",
"IP": "10.211.55.10"
},
{
"Name": "202290dfb303",
"IP": "10.211.55.22"
},
{
"Name": "b1b45c422a80",
"IP": "10.211.55.18"
}
]
}
]
- docker_gwbridge 网络详情
- bridge网络
- IP 172.18.0.0/16，网关 172.18.0.1
[root@centos7-10 ~]# docker network inspect docker_gwbridge
[
{
"Name": "docker_gwbridge",
"Id": "333348eb8ff434a7be478f93741588da9624bbab0b0787e5c68f2696816d3909",
"Created": "2024-02-22T13:42:37.480107344+08:00",
"Scope": "local",
"Driver": "bridge",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": [
{
"Subnet": "172.18.0.0/16",
"Gateway": "172.18.0.1"
}
]
},
"Internal": false,
"Attachable": false,
"Ingress": false,
"ConfigFrom": {
"Network": ""
},
"ConfigOnly": false,
"Containers": {
"86e2f87808941e12b5912ec5ee922dc48b04fbb4ce035189323eda51d4b74cac": {
"Name": "gateway_a567c55696f4",
"EndpointID": "f9af1ab146a6cfe6be4df5b3c848e87c017251f0edd4482474ca1959d9ddb3df",
"MacAddress": "02:42:ac:12:00:03",
"IPv4Address": "172.18.0.3/16",
"IPv6Address": ""
},
"ingress-sbox": {
"Name": "gateway_ingress-sbox",
"EndpointID": "6f7823fd4b2c2fb825213d5aa8b9e05cd3f7e286597b5ecba62dc474aeb748fb",
"MacAddress": "02:42:ac:12:00:02",
"IPv4Address": "172.18.0.2/16",
"IPv6Address": ""
}
},
"Options": {
"com.docker.network.bridge.enable_icc": "false",
"com.docker.network.bridge.enable_ip_masquerade": "true",
"com.docker.network.bridge.name": "docker_gwbridge"
},
"Labels": {}
}
]
- 集群运行my-nginx服务，副本数3
[root@centos7-10 ~]# docker service ls
ID NAME MODE REPLICAS IMAGE PORTS
7rfsp2zazavr my-nginx replicated 3/3 nginx-sj:2024022601 *:9090->80/tcp
- my-nginx服务详情
- 运行nginx容器镜像
- 发布端口9090，容器内nginx端口80
- 服务发布方式ingress
- ingress网络VIP 10.0.0.15/24
[root@centos7-10 ~]# docker service inspect my-nginx
[
{
"ID": "7rfsp2zazavrnckuw074dv8dl",
"Version": {
"Index": 1726
},
"CreatedAt": "2024-02-26T09:59:24.571367943Z",
"UpdatedAt": "2024-03-06T05:36:56.386485665Z",
"Spec": {
"Name": "my-nginx",
"Labels": {},
"TaskTemplate": {
"ContainerSpec": {
"Image": "nginx-sj:2024022601",
"Init": false,
"Mounts": [
{
"Type": "volume",
"Source": "my-volume",
"Target": "/usr/share/nginx/html/"
}
],
"StopGracePeriod": 10000000000,
"DNSConfig": {},
"Isolation": "default"
},
"Resources": {
"Limits": {},
"Reservations": {}
},
"RestartPolicy": {
"Condition": "any",
"Delay": 5000000000,
"MaxAttempts": 0
},
"Placement": {},
"Networks": [
{
"Target": "9u6c1vlfy4kvli7ihka8f5mjf"
}
],
"ForceUpdate": 0,
"Runtime": "container"
},
"Mode": {
"Replicated": {
"Replicas": 3
}
},
"UpdateConfig": {
"Parallelism": 1,
"FailureAction": "pause",
"Monitor": 5000000000,
"MaxFailureRatio": 0,
"Order": "stop-first"
},
"RollbackConfig": {
"Parallelism": 1,
"FailureAction": "pause",
"Monitor": 5000000000,
"MaxFailureRatio": 0,
"Order": "stop-first"
},
"EndpointSpec": {
"Mode": "vip",
"Ports": [
{
"Protocol": "tcp",
"TargetPort": 80,
"PublishedPort": 9090,
"PublishMode": "ingress"
}
]
}
},
"PreviousSpec": {
"Name": "my-nginx",
"Labels": {},
"TaskTemplate": {
"ContainerSpec": {
"Image": "nginx-sj:2024022601",
"Init": false,
"Mounts": [
{
"Type": "volume",
"Source": "my-volume",
"Target": "/usr/share/nginx/html/"
}
],
"DNSConfig": {},
"Isolation": "default"
},
"Resources": {
"Limits": {},
"Reservations": {}
},
"Placement": {},
"Networks": [
{
"Target": "9u6c1vlfy4kvli7ihka8f5mjf"
}
],
"ForceUpdate": 0,
"Runtime": "container"
},
"Mode": {
"Replicated": {
"Replicas": 4
}
},
"EndpointSpec": {
"Mode": "vip",
"Ports": [
{
"Protocol": "tcp",
"TargetPort": 80,
"PublishedPort": 9090,
"PublishMode": "ingress"
}
]
}
},
"Endpoint": {
"Spec": {
"Mode": "vip",
"Ports": [
{
"Protocol": "tcp",
"TargetPort": 80,
"PublishedPort": 9090,
"PublishMode": "ingress"
}
]
},
"Ports": [
{
"Protocol": "tcp",
"TargetPort": 80,
"PublishedPort": 9090,
"PublishMode": "ingress"
}
],
"VirtualIPs": [
{
"NetworkID": "9j40lm9s5dtedg04r6jywqr1k",
"Addr": "10.0.0.15/24"
},
{
"NetworkID": "9u6c1vlfy4kvli7ihka8f5mjf",
"Addr": "172.16.0.27/16"
}
]
}
}
]
7 Swarm集群数据包转发流程
7.1 Client发送请求至集群节点9090端口
7.1.1 集群节点宿主机Netfilter规则
- Iptables 查看NAT表
- Chain PREROUTING 和 OUTPUT，把目的地址类型是宿主机系统本地地址的数据包，在数据包进入NAT表PREROUTING和OUTPUT时，让它们直接jump到DOCKER-INGRESS的链。
说明：PREROUTING链处理外部发起请求的数据包，OUTPUT链处理本机发起请求的数据包 - Chain DOCKER-INGRESS 把TCP协议 发往目的端口9090的数据包（集群服务对外发布的端口）进行DNAT，修改目的地址，发往172.18.0.2:9090
说明：172.18.0.2配置在ingress_sbox命名空间的网卡上，该网卡与宿主机默认命名空间下网卡是一对veth pair（详见上述Swarm 网络连接图）。
- Chain PREROUTING 和 OUTPUT，把目的地址类型是宿主机系统本地地址的数据包，在数据包进入NAT表PREROUTING和OUTPUT时，让它们直接jump到DOCKER-INGRESS的链。
// 查看节点centos7-10 的nat表。集群内其他节点相同，不一一例举了。
[root@centos7-10 ~]# iptables -L -nv -t nat
Chain PREROUTING (policy ACCEPT 13068 packets, 1352K bytes)
pkts bytes target prot opt in out source destination
9629 585K DOCKER-INGRESS all -- * * 0.0.0.0/0 0.0.0.0/0 ADDRTYPE match dst-type LOCAL
9560 581K DOCKER all -- * * 0.0.0.0/0 0.0.0.0/0 ADDRTYPE match dst-type LOCAL
......
Chain DOCKER-INGRESS (2 references)
pkts bytes target prot opt in out source destination
75 4800 DNAT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:9090 to:172.18.0.2:9090
9565 581K RETURN all -- * * 0.0.0.0/0 0.0.0.0/0
- Iptables 查看Filter表
- Chain FORWARD链 将转发数据包jump到DOCKER-INGRESS的链
- Chain DOCKER-INGRESS链，放行向内发送至9090端口的TCP数据包和9090端口向外回复的TCP数据包（其实就是禁止9090主动向外发起连接，不允许NEW）
[root@centos7-10 ~]# iptables -L -nv -t filter
Chain INPUT (policy ACCEPT 375K packets, 47M bytes)
pkts bytes target prot opt in out source destination
Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
120 9960 DOCKER-USER all -- * * 0.0.0.0/0 0.0.0.0/0
120 9960 DOCKER-INGRESS all -- * * 0.0.0.0/0 0.0.0.0/0
2208 1526K DOCKER-ISOLATION-STAGE-1 all -- * * 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT all -- * docker0 0.0.0.0/0 0.0.0.0/0 ctstate RELATED,ESTABLISHED
0 0 DOCKER all -- * docker0 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT all -- docker0 !docker0 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT all -- docker0 docker0 0.0.0.0/0 0.0.0.0/0
1408 1492K ACCEPT all -- * docker_gwbridge 0.0.0.0/0 0.0.0.0/0 ctstate RELATED,ESTABLISHED
0 0 DOCKER all -- * docker_gwbridge 0.0.0.0/0 0.0.0.0/0
800 34026 ACCEPT all -- docker_gwbridge !docker_gwbridge 0.0.0.0/0 0.0.0.0/0
0 0 DROP all -- docker_gwbridge docker_gwbridge 0.0.0.0/0 0.0.0.0/0
Chain OUTPUT (policy ACCEPT 344K packets, 45M bytes)
pkts bytes target prot opt in out source destination
Chain DOCKER (2 references)
pkts bytes target prot opt in out source destination
Chain DOCKER-INGRESS (1 references)
pkts bytes target prot opt in out source destination
525 35100 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:9090
375 39600 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED tcp spt:9090
2208 1526K RETURN all -- * * 0.0.0.0/0 0.0.0.0/0
......
- 查看docker命名空间
// 将容器命名空间目录连接到/var/run/netns
[root@centos7-10 ~]# ln -s /var/run/docker/netns/ /var/run/netns
// 查看命名空间
[root@centos7-10 ~]# ip netns show
a567c55696f4 (id: 4) // 容器命名空间，每个容器1个
1-9u6c1vlfy4 (id: 2) // 自定义Overlay网络命名空间，本文请忽略
lb_9u6c1vlfy (id: 3) // 自定义Overlay网络命名空间，本文请忽略
1-9j40lm9s5d (id: 0) // ingess网络命名空间，包含Vxlan VTEP（VXLAN Tunnel Endpoints）
ingress_sbox (id: 1) // ingess网络命名空间，网络入口，启用IPVS负载均衡
- 查看ingress_sbox命名空间网卡信息
- eth1: 172.18.0.2，与宿主机默认命名空间下网卡是一对veth pair，接收外部请求数据包，所有集群节点上都一样。
- eth0: 10.0.0.15/32是ingress网络VIP，但是被隐藏了，可以接收数据包；10.0.0.2/24是实际使用的IP，连接ingress网络。集群中每个节点使用的IP不同，例如节点centos7-18上使用10.0.0.3/24。
[root@centos7-10 ~]# ip netns exec ingress_sbox ip a
......
6: eth0@if7: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue state UP group default
link/ether 02:42:0a:00:00:02 brd ff:ff:ff:ff:ff:ff link-netnsid 0
inet 10.0.0.2/24 brd 10.0.0.255 scope global eth0
valid_lft forever preferred_lft forever
inet 10.0.0.15/32 scope global eth0
valid_lft forever preferred_lft forever
8: eth1@if9: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default
link/ether 02:42:ac:12:00:02 brd ff:ff:ff:ff:ff:ff link-netnsid 1
inet 172.18.0.2/16 brd 172.18.255.255 scope global eth1
valid_lft forever preferred_lft forever
7.1.2 Tcpdump抓包验证结果
验证流程：curl http://10.211.55.10:9090 --> 10.211.55.90:9090 --> 172.18.0.2:9090
验证结果：
- Client（10.211.55.2） curl http://10.211.55.10:9090
// curl http://10.211.55.10:9090
jinshideMacBook-Pro-2:~ shijin$ curl http://10.211.55.10:9090/index1.html
// 容器nginx服务显示每个集群节点宿主机的IP
Host IP is 10.211.55.10
- tcpdump抓宿主机物理网卡enp0s5
- 接收请求数据包：10.211.55.2.51883 > 10.211.55.10.9090，
// 查看enp0s5信息
[root@centos7-10 ~]# ip a show enp0s5
2: enp0s5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 00:1c:42:ae:b6:41 brd ff:ff:ff:ff:ff:ff
inet 10.211.55.10/24 brd 10.211.55.255 scope global noprefixroute dynamic enp0s5
valid_lft 1502sec preferred_lft 1502sec
inet6 fdb2:2c26:f4e4:0:cd1f:12f3:4076:6d89/64 scope global noprefixroute dynamic
valid_lft 2591770sec preferred_lft 604570sec
inet6 fe80::7e0c:1902:e1ca:4324/64 scope link noprefixroute
valid_lft forever preferred_lft forever
inet6 fe80::567a:248b:5e94:5d19/64 scope link noprefixroute
valid_lft forever preferred_lft forever
// 抓宿主机物理网卡enp0s5
[root@centos7-10 ~]# tcpdump -nnnv -i enp0s5 port 9090
tcpdump: listening on enp0s5, link-type EN10MB (Ethernet), capture size 262144 bytes
15:41:33.029847 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto TCP (6), length 64)
10.211.55.2.51883 > 10.211.55.10.9090: Flags [SEW], cksum 0xf5aa (correct), seq 1488146503, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1319360275 ecr 0,sackOK,eol], length 0
15:41:33.030088 IP (tos 0x0, ttl 62, id 0, offset 0, flags [DF], proto TCP (6), length 60)
10.211.55.10.9090 > 10.211.55.2.51883: Flags [S.E], cksum 0x83e0 (incorrect -> 0x46cb), seq 3176725104, ack 1488146504, win 27960, options [mss 1410,sackOK,TS val 100373895 ecr 1319360275,nop,wscale 7], length 0
- tcpdump抓ingress_sbox命名空间下eth1网卡(172.18.0.2)
- DNAT转发数据包：10.211.55.2.51883 > 172.18.0.2.9090
// 外部请求数据包已经转发至172.18.0.2.9090
[root@centos7-10 ~]# ip netns exec ingress_sbox tcpdump -nnnv -i eth1
tcpdump: listening on eth1, link-type EN10MB (Ethernet), capture size 262144 bytes
15:41:33.029944 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto TCP (6), length 64)
10.211.55.2.51883 > 172.18.0.2.9090: Flags [SEW], cksum 0x8b73 (correct), seq 1488146503, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1319360275 ecr 0,sackOK,eol], length 0
15:41:33.030079 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto TCP (6), length 60)
172.18.0.2.9090 > 10.211.55.2.51883: Flags [S.E], cksum 0xee17 (incorrect -> 0xdc93), seq 3176725104, ack 1488146504, win 27960, options [mss 1410,sackOK,TS val 100373895 ecr 1319360275,nop,wscale 7], length 0
7.2 Ingress_sbox下IPVS负载均衡数据包
以节点centos7-10为例
7.2.1 Ingress_sbox下Netfilter规则
- Iptables 查看MANGLE表
- Chain PREROUTING，将TCP协议 发往目的端口9090的数据包，在进入MANGLE表PREROUTING时，给它们打上标记0x102（十进制 258）。
说明：打标记是为了IPVS根据标记识别转发数据包 - Chain INPUT 将发往10.0.0.15（ingress网络的VIP）的数据包，在进入INPUT时，给它们打上标记0x102（十进制 258）
说明：打标记是为了IPVS根据标记识别转发数据包。
- Chain PREROUTING，将TCP协议 发往目的端口9090的数据包，在进入MANGLE表PREROUTING时，给它们打上标记0x102（十进制 258）。
[root@centos7-10 ~]# ip netns exec ingress_sbox iptables -L -nv -t mangle
Chain PREROUTING (policy ACCEPT 949 packets, 78785 bytes)
pkts bytes target prot opt in out source destination
547 36556 MARK tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:9090 MARK set 0x102
Chain INPUT (policy ACCEPT 559 packets, 37601 bytes)
pkts bytes target prot opt in out source destination
0 0 MARK all -- * * 0.0.0.0/0 10.0.0.15 MARK set 0x102
......
- Iptables 查看NAT表
- Chain POSTROUTING，把发往10.0.0.0/24的数据包（ingess网络地址段）进行SNAT，修改数据包源地址为10.0.0.2。
说明：10.0.0.2是集群节点Centos7-10上ingress网络入口地址，每个节点IP不同且在ingess网络中唯一，例如节点Centos7-18的ingress网络入口地址是10.0.0.3
说明："ipvs to:10.0.0.2"含义。查看详情iptables -L -nvv -t nat，看到这条规则的Protocol: 0、Match name: `ipvs’。protocol为0时，会自动选择type类型对应的默认协议。
- Chain POSTROUTING，把发往10.0.0.0/24的数据包（ingess网络地址段）进行SNAT，修改数据包源地址为10.0.0.2。
[root@centos7-10 ~]# ip netns exec ingress_sbox iptables -L -nv -t nat
Chain PREROUTING (policy ACCEPT 79 packets, 5076 bytes)
pkts bytes target prot opt in out source destination
Chain INPUT (policy ACCEPT 1 packets, 84 bytes)
pkts bytes target prot opt in out source destination
Chain OUTPUT (policy ACCEPT 8 packets, 546 bytes)
pkts bytes target prot opt in out source destination
0 0 DOCKER_OUTPUT all -- * * 0.0.0.0/0 127.0.0.11
Chain POSTROUTING (policy ACCEPT 8 packets, 546 bytes)
pkts bytes target prot opt in out source destination
0 0 DOCKER_POSTROUTING all -- * * 0.0.0.0/0 127.0.0.11
78 4992 SNAT all -- * * 0.0.0.0/0 10.0.0.0/24 ipvs to:10.0.0.2
......
7.2.2 Ingress_sbox下IPVS规则
- ipvsadm 查看IPVS规则
- FWM（firewall-mark）等于258（十六进制0x102）。
说明：使用FWM识别进行负载均衡；rr 表示轮询算法，当前有3台Real server（容器）；Masq表示 NAT模式，详见：IPVS之NAT转发模式。
- FWM（firewall-mark）等于258（十六进制0x102）。
[root@centos7-10 ~]# ip netns exec ingress_sbox ipvsadm -L -n
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
-> RemoteAddress:Port Forward Weight ActiveConn InActConn
FWM 258 rr
-> 10.0.0.17:0 Masq 1 0 0
-> 10.0.0.20:0 Masq 1 0 0
-> 10.0.0.21:0 Masq 1 0 0
[root@centos7-10 ~]#
7.2.3 Tcpdump抓包验证结果
验证流程：curl http://10.211.55.10:9090 --> 10.211.55.90:9090 --> 172.18.0.2:9090 --> IPVS --> 1-9j40lm9s5d命名空间
验证结果：
- Client（10.211.55.2） curl http://10.211.55.10:9090 3次
jinshideMacBook-Pro-2:~ shijin$ curl http://10.211.55.10:9090/index1.html
Host IP is 10.211.55.18
jinshideMacBook-Pro-2:~ shijin$ curl http://10.211.55.10:9090/index1.html
Host IP is 10.211.55.22
jinshideMacBook-Pro-2:~ shijin$ curl http://10.211.55.10:9090/index1.html
Host IP is 10.211.55.10
- ipvsadm查看连接
- 看到ipvs负载均衡了3次请求，每个Real IP 一次
[root@centos7-10 ~]# ip netns exec ingress_sbox ipvsadm -L -n -c
IPVS connection entries
pro expire state source virtual destination
TCP 01:44 TIME_WAIT 10.211.55.2:57786 172.18.0.2:9090 10.0.0.20:9090
TCP 01:49 TIME_WAIT 10.211.55.2:57800 172.18.0.2:9090 10.0.0.21:9090
TCP 01:52 TIME_WAIT 10.211.55.2:57807 172.18.0.2:9090 10.0.0.17:9090
- tcpdump抓ingress_sbox下eth0(10.0.0.2/24和10.0.0.15/32)
- 转发请求数据包：10.0.0.2.57786 > 10.0.0.20.9090
- 转发请求数据包：10.0.0.2.57800 > 10.0.0.21.9090
- 转发请求数据包：10.0.0.2.57807 > 10.0.0.17.9090
// 10.0.0.2.57786 > 10.0.0.20.9090
17:52:51.203834 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto TCP (6), length 64)
10.0.0.2.57786 > 10.0.0.20.9090: Flags [SEW], cksum 0xd7ab (correct), seq 968936781, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1327886090 ecr 0,sackOK,eol], length 0
17:52:51.204644 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto TCP (6), length 60)
10.0.0.20.9090 > 10.0.0.2.57786: Flags [S.E], cksum 0x7b1a (correct), seq 3086272880, ack 968936782, win 27960, options [mss 1410,sackOK,TS val 108230949 ecr 1327886090,nop,wscale 7], length 0
// 10.0.0.2.57800 > 10.0.0.21.9090
17:52:57.148304 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto TCP (6), length 64)
10.0.0.2.57800 > 10.0.0.21.9090: Flags [SEW], cksum 0x3f51 (correct), seq 4174221620, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1327891553 ecr 0,sackOK,eol], length 0
17:52:57.148775 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto TCP (6), length 60)
10.0.0.21.9090 > 10.0.0.2.57800: Flags [S.E], cksum 0xc796 (correct), seq 3791952458, ack 4174221621, win 27960, options [mss 1410,sackOK,TS val 101489099 ecr 1327891553,nop,wscale 7], length 0
// 10.0.0.2.57807 > 10.0.0.17.9090
17:52:59.366754 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto TCP (6), length 64)
10.0.0.2.57807 > 10.0.0.17.9090: Flags [SEW], cksum 0xab41 (correct), seq 3929549799, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1327893584 ecr 0,sackOK,eol], length 0
17:52:59.366977 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto TCP (6), length 60)
10.0.0.17.9090 > 10.0.0.2.57807: Flags [S.E], cksum 0x1441 (incorrect -> 0x693f), seq 3691124848, ack 3929549800, win 27960, options [mss 1410,sackOK,TS val 108260232 ecr 1327893584,nop,wscale 7], length 0
7.3 1-9j40lm9s5d下实现跨主机网络通讯
7.3.1 1-9j40lm9s5d下的网络连接
从上图中可见，Centos7-10节点1的1-9j40lm9s5d命名空间下，有Linux bridge br0。br0共接入了3个接口（网卡），同时负责接口间的网络通讯，其中：
- 5: vxlan0@if53：是Vxlan的VTEP，通过跨主机（节点）建立vxlan隧道，组建ingress网络。其他节点上相同命名空间下也有Vxlan的VTEP，例如上图中Centos7-18节点。
- 7: veth0@if6：与命名空间ingress_sbox下eth0是Veth pair，负责转发进入ingress网络的数据包。
- 62: veth7@if61：与容器命名空间a567c55696f4下的eth0是Veth pair，负责转发容器的数据包。
- 1-9j40lm9s5d下br0的情况
[root@centos7-10 ~]# ip netns exec 1-9j40lm9s5d brctl show
bridge name bridge id STP enabled interfaces
br0 8000.32f9e45ee4ae no veth0
veth7
vxlan0
- 1-9j40lm9s5d下接口（网卡）情况
[root@centos7-10 ~]# ip netns exec 1-9j40lm9s5d ip a
......
2: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue state UP group default
link/ether 32:f9:e4:5e:e4:ae brd ff:ff:ff:ff:ff:ff
inet 10.0.0.1/24 brd 10.0.0.255 scope global br0
valid_lft forever preferred_lft forever
5: vxlan0@if5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue master br0 state UNKNOWN group default
link/ether 32:f9:e4:5e:e4:ae brd ff:ff:ff:ff:ff:ff link-netnsid 0
7: veth0@if6: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue master br0 state UP group default
link/ether 52:65:8a:62:c2:b0 brd ff:ff:ff:ff:ff:ff link-netnsid 1
62: veth7@if61: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue master br0 state UP group default
link/ether ee:55:4f:3f:9f:ed brd ff:ff:ff:ff:ff:ff link-netnsid 2
7.3.2 1-9j40lm9s5d下Vxlan规则
上图中的5: vxlan0@if53是Vxlan的VTEP（VXLAN Tunnel Endpoints），它与Centos7-18和Centos7-22上的VTEP组成跨主机的ingress Overlay网络。每个主机内的VTEP均接入br0，通过br0将ingress外部入口和内部容器接入ingress网络，从而能够将访问IPVS的外部请求负载均衡到多个节点的容器（Real server）上
- 查看5: vxlan0@if5（vxlan id 4096）
[root@centos7-10 ~]# ip netns exec 1-9j40lm9s5d ip -d link show type vxlan
5: vxlan0@if5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue master br0 state UNKNOWN mode DEFAULT group default
link/ether 32:f9:e4:5e:e4:ae brd ff:ff:ff:ff:ff:ff link-netnsid 0 promiscuity 1
vxlan id 4096 srcport 0 0 dstport 4789 proxy l2miss l3miss ageing 300 noudpcsum noudp6zerocsumtx noudp6zerocsumrx
bridge_slave state forwarding priority 32 cost 100 hairpin off guard off root_block off fastleave off learning on flood on port_id 0x8001 port_no 0x1 designated_port 32769 designated_cost 0 designated_bridge 8000.32:f9:e4:5e:e4:ae designated_root 8000.32:f9:e4:5e:e4:ae hold_timer 0.00 message_age_timer 0.00 forward_delay_timer 0.00 topology_change_ack 0 config_pending 0 proxy_arp off proxy_arp_wifi off mcast_router 1 mcast_fast_leave off mcast_flood on addrgenmode eui64 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535
- 查看ingress网络Vxlan隧道
[root@centos7-10 ~]# ip netns exec 1-9j40lm9s5d bridge -d fdb show dev vxlan0
32:f9:e4:5e:e4:ae master br0 permanent
// Centos7-18节点ingress_sbox下eh0(10.0.0.3)的mac
02:42:0a:00:00:03 dst 10.211.55.18 link-netnsid 0 self permanent
// Centos7-18节点容器7fd6d0335ad4的eh0(10.0.0.20)的mac
02:42:0a:00:00:14 dst 10.211.55.18 link-netnsid 0 self permanent
02:42:0a:00:00:04 dst 10.211.55.22 link-netnsid 0 self permanent
02:42:0a:00:00:15 dst 10.211.55.22 link-netnsid 0 self permanent
7.3.3 Tcpdump抓包验证结果（容器在当前节点）
验证流程：curl http://10.211.55.10:9090 --> 10.211.55.90:9090 --> 172.18.0.2:9090 --> IPVS --> 1-9j40lm9s5d下br0 --> 当前节点的容器（real server）
验证结果：
- Client（10.211.55.2） curl http://10.211.55.10:9090，访问当前节点（10.211.55.10）的容器
jinshideMacBook-Pro-2:~ shijin$ curl http://10.211.55.10:9090/index1.html
// 容器内nginx服务显示结果，显示宿主机IP
Host IP is 10.211.55.10
jinshideMacBook-Pro-2:~ shijin$
- tcpdump抓1-9j40lm9s5d下br0(32:f9:e4:5e:e4:ae)
- 转发请求数据包：10.0.0.2.55022 > 10.0.0.17.9090
说明：10.0.0.17是Centos7-10同节点下容器网卡61: eth0@if62的IP
- 转发请求数据包：10.0.0.2.55022 > 10.0.0.17.9090
// 抓1-9j40lm9s5d下br0
[root@centos7-10 ~]# ip netns exec 1-9j40lm9s5d tcpdump -nnnv -i br0
tcpdump: listening on br0, link-type EN10MB (Ethernet), capture size 262144 bytes
15:04:21.151015 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto TCP (6), length 64)
10.0.0.2.55022 > 10.0.0.17.9090: Flags [SEW], cksum 0xa206 (correct), seq 2680037566, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1340372305 ecr 0,sackOK,eol], length 0
15:04:21.151137 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto TCP (6), length 60)
10.0.0.17.9090 > 10.0.0.2.55022: Flags [S.E], cksum 0x1441 (incorrect -> 0x4cd5), seq 2459281603, ack 2680037567, win 27960, options [mss 1410,sackOK,TS val 120829713 ecr 1340372305,nop,wscale 7], length 0
- tcpdump抓1-9j40lm9s5d下veth7(与容器内eth0 10.0.0.17是Veth pair)
- 转发请求数据包：10.0.0.2.55022 > 10.0.0.17.9090
// 抓1-9j40lm9s5d下veth7
[root@centos7-10 ~]# ip netns exec 1-9j40lm9s5d tcpdump -nnnv -i veth7
tcpdump: listening on veth7, link-type EN10MB (Ethernet), capture size 262144 bytes
15:04:21.151032 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto TCP (6), length 64)
10.0.0.2.55022 > 10.0.0.17.9090: Flags [SEW], cksum 0xa206 (correct), seq 2680037566, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1340372305 ecr 0,sackOK,eol], length 0
15:04:21.151137 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto TCP (6), length 60)
10.0.0.17.9090 > 10.0.0.2.55022: Flags [S.E], cksum 0x1441 (incorrect -> 0x4cd5), seq 2459281603, ack 2680037567, win 27960, options [mss 1410,sackOK,TS val 120829713 ecr 1340372305,nop,wscale 7], length 0
7.3.4 Tcpdump抓包验证结果（容器在其它节点）
验证流程：curl http://10.211.55.10:9090 --> 10.211.55.90:9090 --> 172.18.0.2:9090 --> IPVS --> 1-9j40lm9s5d下br0 --> vxlan0（Vxlan VTEP）–> 其它节点的vxlan0（Vxlan VTEP）–> 其它节点的容器（real server）
验证结果：
- Client（10.211.55.2） curl http://10.211.55.10:9090，访问其它节点（10.211.55.18）的容器
jinshideMacBook-Pro-2:~ shijin$ curl http://10.211.55.10:9090/index1.html
// 容器内nginx服务显示结果，显示宿主机IP
Host IP is 10.211.55.18
- 节点Centos7-10上tcpdump抓1-9j40lm9s5d下br0(32:f9:e4:5e:e4:ae)
- 转发请求数据包：10.0.0.2.60559 > 10.0.0.20.9090
说明：10.0.0.20是Centos7-18节点下容器网卡51: eth0@if52的IP
- 转发请求数据包：10.0.0.2.60559 > 10.0.0.20.9090
[root@centos7-10 ~]# ip netns exec 1-9j40lm9s5d tcpdump -nnnv -i br0
tcpdump: listening on br0, link-type EN10MB (Ethernet), capture size 262144 bytes
15:40:51.450406 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto TCP (6), length 64)
10.0.0.2.60559 > 10.0.0.20.9090: Flags [SEW], cksum 0x44b4 (correct), seq 3572036980, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1342550781 ecr 0,sackOK,eol], length 0
15:40:51.450845 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto TCP (6), length 60)
10.0.0.20.9090 > 10.0.0.2.60559: Flags [S.E], cksum 0x0fd9 (correct), seq 499769354, ack 3572036981, win 27960, options [mss 1410,sackOK,TS val 122999839 ecr 1342550781,nop,wscale 7], length 0
- 节点centos7-10上tcpdump抓1-9j40lm9s5d下vxlan0
- 转发请求数据包：10.0.0.2.55022 > 10.0.0.20.9090
说明：10.0.0.20是其它节点Centos7-18上的容器IP，需要通过ingress网络跨主机通讯，因此会经过Centos7-10的1-9j40lm9s5d下的vxlan0（Vxlan VTEP）。
- 转发请求数据包：10.0.0.2.55022 > 10.0.0.20.9090
[root@centos7-10 ~]# ip netns exec 1-9j40lm9s5d tcpdump -nnnv -i vxlan0
tcpdump: listening on vxlan0, link-type EN10MB (Ethernet), capture size 262144 bytes
15:40:51.450418 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto TCP (6), length 64)
10.0.0.2.60559 > 10.0.0.20.9090: Flags [SEW], cksum 0x44b4 (correct), seq 3572036980, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1342550781 ecr 0,sackOK,eol], length 0
15:40:51.450845 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto TCP (6), length 60)
10.0.0.20.9090 > 10.0.0.2.60559: Flags [S.E], cksum 0x0fd9 (correct), seq 499769354, ack 3572036981, win 27960, options [mss 1410,sackOK,TS val 122999839 ecr 1342550781,nop,wscale 7], length 0
- 节点centos7-18上tcpdump抓物理网卡enp0s5
- 转发请求数据包：VXLAN 外层UDP 10.211.55.10.45803 > 10.211.55.18.4789；内层TCP 10.0.0.2.60559 > 10.0.0.20.9090
说明：ingress网络是在物理网络上建立的Vxlan隧道，数据包会通过centos7-10和centos7-18的物理网卡enp0s5。 - tcpdump ‘udp[39]=6 and (udp[42:4]=0x0a000002 or udp[42:4]=0x0a000014)’ -nnnv -e -i enp0s5 含义是：抓协议报文中UDP header 启始位置0偏移至39字节处（inner IP header中protocol）的值等于6（协议号6=tcp）并且协议报文中UDP header 启始位置0偏移至42字节处（inner IP header中 Source Address）、长度4字节的值是0x0a000002或0x0a000014。
说明：0x0a000002是10.0.0.2的十六进制，0x0a000014是10.0.0.20的十六进制。tcpdump命令详细解析，请见我另一篇笔记：tcpdump使用pcap-filter抓Vxlan包内数据
- 转发请求数据包：VXLAN 外层UDP 10.211.55.10.45803 > 10.211.55.18.4789；内层TCP 10.0.0.2.60559 > 10.0.0.20.9090
// 在centos7-18 上抓enp0s5的UDP包
[root@centos7-18 ~]# tcpdump 'udp[39]=6 and (udp[42:4]=0x0a000002 or udp[42:4]=0x0a000014)' -nnnv -e -i enp0s5
tcpdump: listening on enp0s5, link-type EN10MB (Ethernet), capture size 262144 bytes
15:40:51.444134 00:1c:42:ae:b6:41 > 00:1c:42:60:87:b2, ethertype IPv4 (0x0800), length 128: (tos 0x0, ttl 64, id 44918, offset 0, flags [none], proto UDP (17), length 114)
10.211.55.10.45803 > 10.211.55.18.4789: VXLAN, flags [I] (0x08), vni 4096
02:42:0a:00:00:02 > 02:42:0a:00:00:14, ethertype IPv4 (0x0800), length 78: (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto TCP (6), length 64)
10.0.0.2.60559 > 10.0.0.20.9090: Flags [SEW], cksum 0x44b4 (correct), seq 3572036980, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1342550781 ecr 0,sackOK,eol], length 0
15:40:51.444366 00:1c:42:60:87:b2 > 00:1c:42:ae:b6:41, ethertype IPv4 (0x0800), length 124: (tos 0x0, ttl 64, id 31402, offset 0, flags [none], proto UDP (17), length 110)
10.211.55.18.38329 > 10.211.55.10.4789: VXLAN, flags [I] (0x08), vni 4096
02:42:0a:00:00:14 > 02:42:0a:00:00:02, ethertype IPv4 (0x0800), length 74: (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto TCP (6), length 60)
10.0.0.20.9090 > 10.0.0.2.60559: Flags [S.E], cksum 0x0fd9 (correct), seq 499769354, ack 3572036981, win 27960, options [mss 1410,sackOK,TS val 122999839 ecr 1342550781,nop,wscale 7], length 0
- 节点centos7-18上tcpdump抓1-9j40lm9s5d下vxlan0
- 转发请求数据包：10.0.0.2.60559 > 10.0.0.20.9090
说明：centos7-18的1-9j40lm9s5d下的vxlan0（Vxlan VTEP）收到从centos7-10传输过来的数据包。
- 转发请求数据包：10.0.0.2.60559 > 10.0.0.20.9090
[root@centos7-18 ~]# ip netns exec 1-9j40lm9s5d tcpdump -nnnv -i vxlan0
tcpdump: listening on vxlan0, link-type EN10MB (Ethernet), capture size 262144 bytes
15:40:51.444193 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto TCP (6), length 64)
10.0.0.2.60559 > 10.0.0.20.9090: Flags [SEW], cksum 0x44b4 (correct), seq 3572036980, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1342550781 ecr 0,sackOK,eol], length 0
15:40:51.444351 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto TCP (6), length 60)
10.0.0.20.9090 > 10.0.0.2.60559: Flags [S.E], cksum 0x1444 (incorrect -> 0x0fd9), seq 499769354, ack 3572036981, win 27960, options [mss 1410,sackOK,TS val 122999839 ecr 1342550781,nop,wscale 7], length 0
7.4 数据包进入容器（Real Server）
7.4.1 节点centos7-18下容器内Netfilter规则
- Iptables 查看NAT表
- Chain PREROUTING，将TCP协议 发往目的地址10.0.0.20（容器网卡eth0）、端口9090的数据包，在进入NAT表PREROUTING时，REDIRECT 端口至80。
说明：发布端口是9090，容器内nginx 服务端口是80。
- Chain PREROUTING，将TCP协议 发往目的地址10.0.0.20（容器网卡eth0）、端口9090的数据包，在进入NAT表PREROUTING时，REDIRECT 端口至80。
[root@centos7-18 ~]# ip netns exec 7fd6d0335ad4 iptables -L -nv -t nat
Chain PREROUTING (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
21 1344 REDIRECT tcp -- * * 0.0.0.0/0 10.0.0.20 tcp dpt:9090 redir ports 80
......
- Iptables 查看Filter表
- Chain INPUT，放行目的地址是10.0.0.20，目的端口是80的数据包。
- Chain OUTPUT，放行源地址是10.0.0.20，源端口是80的已建立连接和相关连接的数据包，但禁止主动向外新建连接的数据包（禁止New）。
[root@centos7-18 ~]# ip netns exec 7fd6d0335ad4 iptables -L -nv -t filter
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
147 9828 ACCEPT tcp -- * * 0.0.0.0/0 10.0.0.20 tcp dpt:80 ctstate NEW,ESTABLISHED
0 0 DROP sctp -- * * 0.0.0.0/0 10.0.0.20
0 0 DROP udp -- * * 0.0.0.0/0 10.0.0.20
0 0 DROP tcp -- * * 0.0.0.0/0 10.0.0.20
Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
105 11088 ACCEPT tcp -- * * 10.0.0.20 0.0.0.0/0 tcp spt:80 ctstate ESTABLISHED
0 0 DROP sctp -- * * 10.0.0.20 0.0.0.0/0
0 0 DROP udp -- * * 10.0.0.20 0.0.0.0/0
0 0 DROP tcp -- * * 10.0.0.20 0.0.0.0/0
7.4.2 Tcpdump抓包验证结果
验证流程：curl http://10.211.55.10:9090 --> 10.211.55.90:9090 --> 172.18.0.2:9090 --> IPVS --> 1-9j40lm9s5d下br0 --> vxlan0（Vxlan VTEP）–> 节点centos7-18的vxlan0（Vxlan VTEP）–> 节点centos7-18下的容器eth0
验证结果：
- Client（10.211.55.2） curl http://10.211.55.10:9090，访问其它节点（10.211.55.18）下的容器
jinshideMacBook-Pro-2:~ shijin$ curl http://10.211.55.10:9090/index1.html
Host IP is 10.211.55.18
- 节点centos7-18上tcpdump抓容器命名空间7fd6d0335ad4下eth0（10.0.0.20）
- 转发请求数据包：10.0.0.2.54718 > 10.0.0.20.9090
[root@centos7-18 ~]# ip netns exec 7fd6d0335ad4 tcpdump -nnnv -i eth0
tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes
16:49:55.214784 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto TCP (6), length 64)
10.0.0.2.54718 > 10.0.0.20.9090: Flags [SEW], cksum 0x7148 (correct), seq 2186891382, win 65535, options [mss 1460,nop,wscale 6,nop,nop,TS val 1346671753 ecr 0,sackOK,eol], length 0
16:49:55.214825 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto TCP (6), length 60)
10.0.0.20.9090 > 10.0.0.2.54718: Flags [S.E], cksum 0x1444 (incorrect -> 0x5a11), seq 589922860, ack 2186891383, win 27960, options [mss 1410,sackOK,TS val 127143610 ecr 1346671753,nop,wscale 7], length 0
8 总结
1. Swarm集群通过IPVS和Overlay网络实现负载均衡。IPVS采用NAT模式对创建服务的所有容器进行负载均衡；VXLAN负责组建Overlay网络，实现跨主机之间的网络通讯。
2. Swarm集群的每个节点，都实现了IPVS的逻辑，都接入了Swarm服务创建的所有容器作为Real Server。