Docker 与 K8S学习笔记（八）—— 自定义容器网络

2023-12-22 08:55:57

我们在上一篇中介绍了Docker中三种网络，none、host和bridge，除了这三种网络，Docker还允许我们创建自定义网络，当我们要创建自定义网络时，Docker提供了三种网络驱动供我们选择：bridge、macvlan和overlay，其中macvlan和ovelay都是用于创建跨主机网络，我们后面在研究，本篇我们主要使用bridge驱动。

一、创建自定义网络

我们通过docker network create命令创建test_net1网络：

$ sudo docker network create --driver bridge test_net1
c7c20444a940135c92958f4434ca2b7428ba17f70a2a8a954a6cf160a011b513
$ sudo docker network ls
NETWORK ID     NAME        DRIVER    SCOPE
6f0087fd32cd   bridge      bridge    local
464b3d11003c   host        host      local
faa8eb8310b4   none        null      local
c7c20444a940   test_net1   bridge    local
$ brctl show
bridge name  bridge id    STP enabled  interfaces
br-c7c20444a940    8000.024200e01cd2  no
docker0    8000.0242cef1fc32  no

我们可以看到，此时系统中新增了一个网桥br-c7c20444a940，其中c7c20444a940就是我们刚刚创建的桥接网络的ID。我们可以看下test_net1的详细配置信息：

$ sudo docker network inspect test_net1
[
    {
        "Name": "test_net1",
        "Id": "c7c20444a940135c92958f4434ca2b7428ba17f70a2a8a954a6cf160a011b513",
        "Created": "2021-10-23T07:07:47.870947684Z",
        "Scope": "local",
        "Driver": "bridge",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": {},
            "Config": [
                {
                    "Subnet": "172.19.0.0/16",
                    "Gateway": "172.19.0.1"
                }
            ]
        },
        "Internal": false,
        "Attachable": false,
        "Ingress": false,
        "ConfigFrom": {
            "Network": ""
        },
        "ConfigOnly": false,
        "Containers": {},
        "Options": {},
        "Labels": {}
    }
]

如果我们在创建网络时，不指定--subnet和--gateway参数时，Docker会自动为其分配网段和网关，我们接着再创建一个网络并指定其网段和网关：

$ sudo docker network create --driver bridge --subnet 173.20.0.0/16 --gateway 173.20.0.1  test_net2
47542e86dc4474779a3b105f1d22f005fc39a529b1f19aa7af2c68297c1c0a41
$ sudo docker network inspect test_net2
[
    {
        "Name": "test_net2",
        "Id": "47542e86dc4474779a3b105f1d22f005fc39a529b1f19aa7af2c68297c1c0a41",
        "Created": "2021-10-23T07:21:47.684305897Z",
        "Scope": "local",
        "Driver": "bridge",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": {},
            "Config": [
                {
                    "Subnet": "173.20.0.0/16",
                    "Gateway": "173.20.0.1"
                }
            ]
        },
        "Internal": false,
        "Attachable": false,
        "Ingress": false,
        "ConfigFrom": {
            "Network": ""
        },
        "ConfigOnly": false,
        "Containers": {},
        "Options": {},
        "Labels": {}
    }
]
$ brctl show
bridge name  bridge id    STP enabled  interfaces
br-47542e86dc44    8000.024273a34080  no
br-c7c20444a940    8000.024200e01cd2  no
docker0    8000.0242cef1fc32  no
$ ifconfig br-47542e86dc44
br-47542e86dc44: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        inet 173.20.0.1  netmask 255.255.0.0  broadcast 173.20.255.255
        ether 02:42:73:a3:40:80  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

二、自定义网络的使用

容易要使用自定义的网络，同样需在启动时通过--network参数指定即可：

$ sudo docker run -it --network=test_net2 busybox
/ # ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
50: eth0@if51: <BROADCAST,MULTICAST,UP,LOWER_UP,M-DOWN> mtu 1500 qdisc noqueue
    link/ether 02:42:ad:14:00:02 brd ff:ff:ff:ff:ff:ff
    inet 173.20.0.2/16 brd 173.20.255.255 scope global eth0
       valid_lft forever preferred_lft forever

我们可以看到Docker会根据容易所使用的网络的网段自动为容器分配IP，当然，容器IP也是可以指定的，即通过--ip参数，但是要注意两点：

只有使用--subnet参数指定网段创建的网络才能指定IP
所指定的IP一定要在所使用的网络的网段中

下图所示的错误就是容器使用的网络并没有通过--subnet指定网段：

$ sudo docker run -it --network=test_net1 --ip 172.19.0.5  busybox
docker: Error response from daemon: user specified IP address is supported only when connecting to networks with user configured subnets.

下图所示的错误是容器所指定IP不在其网络的指定网段内：

$ sudo docker run -it --network=test_net2 --ip 172.20.0.2  busybox
ERRO[0000] error waiting for container: context canceled
docker: Error response from daemon: Invalid address 172.20.0.2: It does not belong to any of this network's subnets.

以下是正确的指定容器IP的例子：

$ sudo docker run -it --network=test_net2 --ip 173.20.0.4  busybox
/ # ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
54: eth0@if55: <BROADCAST,MULTICAST,UP,LOWER_UP,M-DOWN> mtu 1500 qdisc noqueue
    link/ether 02:42:ad:14:00:04 brd ff:ff:ff:ff:ff:ff
    inet 173.20.0.4/16 brd 173.20.255.255 scope global eth0
       valid_lft forever preferred_lft forever

三、Docker网络隔离及原理

到目前位置我们创建使用test_net2网络创建了两个容器，那么这两个容器网络应该是互通的，我们来验证一下：

$ sudo docker run -it --network=test_net2 --ip 173.20.0.4  busybox
/ # ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
54: eth0@if55: <BROADCAST,MULTICAST,UP,LOWER_UP,M-DOWN> mtu 1500 qdisc noqueue
    link/ether 02:42:ad:14:00:04 brd ff:ff:ff:ff:ff:ff
    inet 173.20.0.4/16 brd 173.20.255.255 scope global eth0
       valid_lft forever preferred_lft forever
/ # ping 173.20.0.2
PING 173.20.0.2 (173.20.0.2): 56 data bytes
64 bytes from 173.20.0.2: seq=0 ttl=64 time=1.319 ms
64 bytes from 173.20.0.2: seq=1 ttl=64 time=0.106 ms
64 bytes from 173.20.0.2: seq=2 ttl=64 time=0.107 ms
^C
--- 173.20.0.2 ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 0.106/0.510/1.319 ms

所以，我们得出结论，使用同一网络创建的容器是能够互通的。相反，如果是不同网络创建的容器应该是无法通信，我们使用test_net1创建一个容器验证一下：

$ sudo docker run -it --network=test_net1 busybox
/ # ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
58: eth0@if59: <BROADCAST,MULTICAST,UP,LOWER_UP,M-DOWN> mtu 1500 qdisc noqueue
    link/ether 02:42:ac:13:00:02 brd ff:ff:ff:ff:ff:ff
    inet 172.19.0.2/16 brd 172.19.255.255 scope global eth0
       valid_lft forever preferred_lft forever
/ # ping 173.20.0.2
PING 173.20.0.2 (173.20.0.2): 56 data bytes
^C
--- 173.20.0.2 ping statistics ---
146 packets transmitted, 0 packets received, 100% packet loss

从结果来看确实无法通信，但是如果我们开启系统的ip forwarding，把当前主机当作路由，那么不同网络应该是能通信的，我们首先来看下系统的配置：

$ ip r
default via 172.16.194.2 dev ens33 proto dhcp src 172.16.194.135 metric 100
172.16.194.0/24 dev ens33 proto kernel scope link src 172.16.194.135
172.16.194.2 dev ens33 proto dhcp scope link src 172.16.194.135 metric 100
172.19.0.0/16 dev br-c7c20444a940 proto kernel scope link src 172.19.0.1
173.20.0.0/16 dev br-47542e86dc44 proto kernel scope link src 173.20.0.1
$ sysctl net.ipv4.ip_forward
net.ipv4.ip_forward = 1

看来我们的主机已经开启了ip forwarding并且172.19.0.0/16和173.20.0.0/16的路由也定义好了，那为什么网络还是不通呢？我们看看iptables：

$ sudo iptables-save
# Generated by iptables-save v1.6.1 on Sat Oct 23 08:19:03 2021
*filter
...
# 如果数据包是从br-47542e86dc44流入但不从br-47542e86dc44流出则跳转到DOCKER-ISOLATION-STAGE-2处理
-A DOCKER-ISOLATION-STAGE-1 -i br-47542e86dc44 ! -o br-47542e86dc44 -j DOCKER-ISOLATION-STAGE-2
# 如果数据包是从br-c7c20444a940流入但不从br-c7c20444a940流出则跳转到DOCKER-ISOLATION-STAGE-2处理
-A DOCKER-ISOLATION-STAGE-1 -i br-c7c20444a940 ! -o br-c7c20444a940 -j DOCKER-ISOLATION-STAGE-2
# 如果数据包是从docker0流入但不从docker0流出则跳转到DOCKER-ISOLATION-STAGE-2处理
-A DOCKER-ISOLATION-STAGE-1 -i docker0 ! -o docker0 -j DOCKER-ISOLATION-STAGE-2
# 如果非以上三种情况则返回上一层处理
-A DOCKER-ISOLATION-STAGE-1 -j RETURN

# 如果数据包流出到br-47542e86dc44则drop
-A DOCKER-ISOLATION-STAGE-2 -o br-47542e86dc44 -j DROP
# 如果数据包流出到br-c7c20444a940则drop
-A DOCKER-ISOLATION-STAGE-2 -o br-c7c20444a940 -j DROP
# 如果数据包流出到docker0则drop
-A DOCKER-ISOLATION-STAGE-2 -o docker0 -j DROP
# 如果非以上三种情况则返回上一层处理
-A DOCKER-ISOLATION-STAGE-2 -j RETURN
-A DOCKER-USER -j RETURN
...

看来原因就在这里了，我们发现Docker创建了一系列网络隔离策略，当数据包流入的网络与流出的网络相同则不作处理，不同则弃数据包，我们通过一个流程图来说明DOCKER-ISOLATION-STAGE-1和DOCKER-ISOLATION-STAGE-2规则的逻辑：

如果我一定要两个使用不同网络的容器通信，该怎么处理呢？也很简单，我们只需要给容器添加对应的网络的的网卡即可，我们通过docker network connect命令可以实现：

# 0da5e260a4b6容器使用的是test_net1，另外两个使用的是test_net2，
# 如果大家在这一步不确定的话可以使用docker inspect 容器id进行确定 
$ sudo docker ps
CONTAINER ID   IMAGE     COMMAND   CREATED       STATUS       PORTS     NAMES
0da5e260a4b6   busybox   "sh"      2 hours ago   Up 2 hours             objective_blackburn
c6871db3efbb   busybox   "sh"      2 hours ago   Up 2 hours             goofy_swartz
c683eacc4eae   busybox   "sh"      2 hours ago   Up 2 hours             modest_swartz
yangye@ayato:~$ sudo docker network connect test_net2 0da5e260a4b6

我们在容器0da5e260a4b6中先ping下173.20.0.2发现网络是通的，我们再看看其网络配置，发现容器中添加了my_net2网络的网卡eth1：

/ # ping 173.20.0.2
PING 173.20.0.2 (173.20.0.2): 56 data bytes
64 bytes from 173.20.0.2: seq=0 ttl=64 time=0.291 ms
64 bytes from 173.20.0.2: seq=1 ttl=64 time=0.100 ms
64 bytes from 173.20.0.2: seq=2 ttl=64 time=0.097 ms
64 bytes from 173.20.0.2: seq=3 ttl=64 time=0.100 ms
64 bytes from 173.20.0.2: seq=4 ttl=64 time=0.147 ms
^C
--- 173.20.0.2 ping statistics ---
5 packets transmitted, 5 packets received, 0% packet loss
round-trip min/avg/max = 0.097/0.147/0.291 ms
/ # ifconfig
eth0      Link encap:Ethernet  HWaddr 02:42:AC:13:00:02
          inet addr:172.19.0.2  Bcast:172.19.255.255  Mask:255.255.0.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:25 errors:0 dropped:0 overruns:0 frame:0
          TX packets:150 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:1830 (1.7 KiB)  TX bytes:14476 (14.1 KiB)

eth1      Link encap:Ethernet  HWaddr 02:42:AD:14:00:03
          inet addr:173.20.0.3  Bcast:173.20.255.255  Mask:255.255.0.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:18 errors:0 dropped:0 overruns:0 frame:0
          TX packets:7 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:1440 (1.4 KiB)  TX bytes:574 (574.0 B)

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

好的，以上就是本篇的内容，下一篇我们再看看容器间通信方式。

码农公寓

相关文章