Dockerfile example for two containers communicating with each other over different networks
25/01/2018 - DOCKER
In this example we are going to create two networks and one container in each. Our aim is to make one container access the other one.
Structure
There are two networks - web_net_1 and web_net_2. There are also two container - app_1_con and app_2_con. The web_net_2 will host both containers but web_net_1 will host only app_1_con. Just because app_1_con is part of web_net_2 network, it can communicate with app_2_con.
Create networks
ubuntu@xenial64:~$ docker network create --subnet 192.168.1.0/24 --driver bridge web_net_1
ubuntu@xenial64:~$ docker network create --subnet 192.168.2.0/24 --driver bridge web_net_2
ubuntu@xenial64:~$ docker network ls
NETWORK ID NAME DRIVER SCOPE
7dca476e7b11 web_net_1 bridge local
9c0f95e63367 web_net_2 bridge local
ubuntu@xenial64:~$ docker network inspect web_net_1
[
{
"Name": "web_net_1",
"Id": "7dca476e7b11accf19618e887e07a3bf8703aaba779382f101e0516558e983ca",
"Created": "2018-01-25T13:46:46.586496294Z",
"Scope": "local",
"Driver": "bridge",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": {},
"Config": [
{
"Subnet": "192.168.1.0/24"
}
]
},
…
}
]
ubuntu@xenial64:~$ docker network inspect web_net_2
[
{
"Name": "web_net_2",
"Id": "9c0f95e63367a3442547b301c425f54b15cd44f2748273ac85c288a881c4e6df",
"Created": "2018-01-25T13:47:02.154334469Z",
"Scope": "local",
"Driver": "bridge",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": {},
"Config": [
{
"Subnet": "192.168.2.0/24"
}
]
},
…
}
]
IP routing
ubuntu@xenial64:~$ route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 10.0.2.2 0.0.0.0 UG 0 0 0 enp0s3
10.0.2.0 0.0.0.0 255.255.255.0 U 0 0 0 enp0s3
172.17.0.0 0.0.0.0 255.255.0.0 U 0 0 0 docker0
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 br-7dca476e7b11
192.168.2.0 0.0.0.0 255.255.255.0 U 0 0 0 br-9c0f95e63367
192.168.99.0 0.0.0.0 255.255.255.0 U 0 0 0 enp0s8
ifconfig
ubuntu@xenial64:~$ ifconfig
br-7dca476e7b11 Link encap:Ethernet HWaddr 02:42:7a:85:6e:76
inet addr:192.168.1.1 Bcast:0.0.0.0 Mask:255.255.255.0
UP BROADCAST MULTICAST MTU:1500 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:0
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
br-9c0f95e63367 Link encap:Ethernet HWaddr 02:42:df:44:6d:3c
inet addr:192.168.2.1 Bcast:0.0.0.0 Mask:255.255.255.0
UP BROADCAST MULTICAST MTU:1500 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:0
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
...
Create application folders and files
ubuntu@xenial64:~$ mkdir app_1
ubuntu@xenial64:~$ mkdir app_2
Dockerfile - app_1
ubuntu@xenial64:~$ nano app_1/Dockerfile
FROM ubuntu:16.04
RUN apt-get update \
&& apt-get install -y \
iputils-ping \
&& rm -rf /var/lib/apt/lists/*
EXPOSE 80
CMD ["/bin/bash"]
Dockerfile - app_2
ubuntu@xenial64:~$ nano app_2/Dockerfile
FROM ubuntu:16.04
RUN apt-get update \
&& apt-get install -y \
iputils-ping \
&& rm -rf /var/lib/apt/lists/*
EXPOSE 80
CMD ["/bin/bash"]
Create images
ubuntu@xenial64:~$ docker build -f app_1/Dockerfile -t app_1_img .
ubuntu@xenial64:~$ docker build -f app_2/Dockerfile -t app_2_img .
Create containers
We are assigning IP addresses to containers and include them in their networks.
ubuntu@xenial64:~$ docker run -i -t -d -p 5011:80 --network=web_net_1 --ip 192.168.1.11 --name=app_1_con app_1_img
ubuntu@xenial64:~$ docker run -i -t -d -p 5022:80 --network=web_net_2 --ip 192.168.2.22 --name=app_2_con app_2_img
ubuntu@xenial64:~$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
84e2bba20bb8 app_2_img "/bin/bash" 5 seconds ago Up 3 seconds 0.0.0.0:5022->80/tcp app_2_con
1fdc83e81490 app_1_img "/bin/bash" 17 seconds ago Up 16 seconds 0.0.0.0:5011->80/tcp app_1_con
As you can see below, each network hosts only one container which will be updated later on.
ubuntu@xenial64:~$ docker network inspect web_net_1
[
{
"Containers": {
"1fdc83e8149090d42b5f635127b54aa406bb0fbf78ce3d9884ec7ae6fb859806": {
"Name": "app_1_con",
"EndpointID": "97f39408338ea52f3813700742e05442229b2426d2abd2b65c3405bdcc608b1c",
"MacAddress": "02:42:c0:a8:01:0b",
"IPv4Address": "192.168.1.11/24",
"IPv6Address": ""
}
}
}
]
ubuntu@xenial64:~$ docker network inspect web_net_2
[
{
"Containers": {
"84e2bba20bb8d0e0abd5166eccb416735d3a2e9b932c2771ea0574f3fd3945f5": {
"Name": "app_2_con",
"EndpointID": "8373a37662cfebe988897b10b7288e3d4d2d8a2cf135f362dd1dec8fee956ee4",
"MacAddress": "02:42:c0:a8:02:16",
"IPv4Address": "192.168.2.22/24",
"IPv6Address": ""
}
}
}
]
Allowing communication
We are adding app_1_con to web_net_2 so app_1_con can talk to app_2_con.
ubuntu@xenial64:~$ docker network connect web_net_2 app_1_con
As you can see below web_net_2 hosts both containers now.
ubuntu@xenial64:~$ docker network inspect web_net_2
[
{
"Containers": {
"0e2ff551a290b4ca2d84c9b282fc99b08cbec7cafef1464ae0df61407b6647fc": {
"Name": "app_2_con",
"EndpointID": "925ca5bef3516dca5e0ae4c9c6483ed5bee44d0f3eaa9ce3e7eaf3c6af50e226",
"MacAddress": "02:42:c0:a8:02:16",
"IPv4Address": "192.168.2.22/24",
"IPv6Address": ""
},
"af6af1fe06d4909be6c270c146a48c1a141bc6283c9aeadb7fa21d04926556cb": {
"Name": "app_1_con",
"EndpointID": "15ae3d50f89e0424d44f80ad43a1b6d257edfd3df1902a2adfd8d3680c2beca9",
"MacAddress": "02:42:c0:a8:02:02",
"IPv4Address": "192.168.2.2/24",
"IPv6Address": ""
}
}
}
]
If you inspect containers as well, you’ll see what networks they are connected to.
Test
Application 1 can communicate with Application 2.
ubuntu@xenial64:~$ docker exec -it app_1_con ping 192.168.2.22
PING 192.168.2.22 (192.168.2.22) 56(84) bytes of data.
64 bytes from 192.168.2.22: icmp_seq=1 ttl=64 time=0.106 ms
64 bytes from 192.168.2.22: icmp_seq=2 ttl=64 time=0.063 ms
64 bytes from 192.168.2.22: icmp_seq=3 ttl=64 time=0.062 ms
64 bytes from 192.168.2.22: icmp_seq=4 ttl=64 time=0.069 ms
64 bytes from 192.168.2.22: icmp_seq=5 ttl=64 time=0.065 ms
Application 2 cannot communicate with Application 1.
ubuntu@xenial64:~$ docker exec -it app_2_con ping 192.168.1.11
PING 192.168.1.11 (192.168.1.11) 56(84) bytes of data.