Docker Networking

Posted on In

Docker Networking

Network Drivers Types

  • bridge - this is the default and most used network driver.
  • host - remove network isolation between host and container, use host’s networking directly. Host mode networking can be useful to optimize performance.
  • overlay - Overlay networks connect multiple Docker daemons together and enable swarm services to communicate with each other.
  • none - disable all networking. Container can’t connect to network. Not used often.

When a container is connected to a network, it can communicate with other containers in the same network.

List Networks

1
docker network ls

default output

1
2
3
4
NETWORK ID          NAME                    DRIVER              SCOPE
cad232899398        bridge                  bridge              local
00cc8b46ebad        host                    host                local
ac75839ac3dd        none                    null                local

Create a Network

use docker network create to create network. use -d or --driver option to set the driver type

1
docker network create -d bridge my-bridge

You can specify the network’s subnet and gateway. The prefix length is 16 by default, here we can specify a subnet with prefix length of24.

1
docker network create -d bridge --subnet 172.66.66.0/24 --gateway 172.66.66.1  my-bridge

run ifconfig on the host machine, you will see a new network interface added.

1
2
3
4
5
6
7
8
$ ifconfig
br-0a428d94b9d5: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        inet 172.66.66.1  netmask 255.255.255.0  broadcast 172.66.66.255
        ether 02:42:e6:8c:27:40  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

Inspect a Network

1
docker network inspect my-bridge

This will show the network information such as Subnet and Gateway information.

It will also contain the containers connected to the network and their IP addresses.

Sample output:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
$ docker network inspect my-bridge
[
    {
        "Name": "my-bridge",
        "Id": "0a428d94b9d528eaf3c52521158e399ec17e7651e98db1eed7570295271bf7db",
        "Created": "2019-09-14T04:13:40.981076739-04:00",
        "Scope": "local",
        "Driver": "bridge",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": {},
            "Config": [
                {
                    "Subnet": "172.66.66.0/24",
                    "Gateway": "172.66.66.1"
                }
            ]
        },
        "Internal": false,
        "Attachable": false,
        "Ingress": false,
        "ConfigFrom": {
            "Network": ""
        },
        "ConfigOnly": false,
        "Containers": {
            "ac3a42c369ee00afffb5170a1bae619cbaa3ca45b0bd630768e6199c322d123b": {
                "Name": "my-alpine",
                "EndpointID": "568a17e9c97ef707eec0f37614a630465bdb0634114639ab4abfb9acd40455b8",
                "MacAddress": "02:42:ac:42:42:02",
                "IPv4Address": "172.66.66.2/24",
                "IPv6Address": ""
            }
        },
        "Options": {},
        "Labels": {}
    }
]

Remove a Network

1
docker network rm my-bridge

Running a container in a Network

use --net=<network> or --network=<network> option to specify the network. <network> is the name of the network to be used

1
docker run -it --rm --network bridge --name my-alpine alpine

Disconnect from a network

1
docker network disconnect bridget my-alpine

Connect to my-bridge network 

1
docker network connect my-bridge my-alpine

The above command will automatically assign an IP address to the container. You can connect to a network with a specified IP address.

1
docker network connect --ip 172.66.66.33 my-bridge  my-alpine

Inspect the container’s network configuration.

1
docker exec my-alpine ifconfig

Example: Run Containers on the Same Network

Here is an example bash script to run both mysql and phpmyadmin container on the same network

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
#!/bin/bash
# Create network
docker network create sample-network

# Create mysql container
docker run  -d --name=mysql \
--network=sample-network \
-e MYSQL_ROOT_PASSWORD=password \
-p 3306:3306 \
mysql:8

# Create phpmyadmin container
docker run -d --name phpmyadmin  \
--network=sample-network \
-e PMA_HOSTS=mysql-dev \
-e PMA_PORT=3306 \
-e PMA_USER=root \
-e PMA_PASSWORD=password \
-p 7000:80 \
phpmyadmin/phpmyadmin

We first create a bridge network called sample-network. Then create mysql and phpmyadmin container that both connect to sample-network.
You can now open phpmyadmin at http://localhost:7000/

Reference