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Bridge-Networks.md

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Bridge network

Most common network type. It is limited to containers within a single host running the Docker engine. Bridge networks are easy to create, manage and troubleshoot.

Two types of Bridge Networks

  • Default bridge network: Docker sets up for you automatically.Best choice for production system.
  • User-defined bridge network: Create and use your own custom bridge networks, to connect containers running on the same Docker host. This is recommended for standalone containers running in production.

Default bridge network

When you start Docker, a default bridge network (also called bridge) is created automatically, and newly-started containers connect to it unless otherwise specified.

We'll start two different alpine containers on the same Docker host.

  1. List current networks:
$ docker network ls
NETWORK ID          NAME                DRIVER              SCOPE
17e324f45964        bridge              bridge              local
6ed54d316334        host                host                local
7092879f2cc8        none                null                local
  1. Start two alpine containers running ash(Alpine’s default shell):
$ docker run -dit --name alpine1 alpine ash
$ docker run -dit --name alpine2 alpine ash
  1. Check that both containers are actually started:
$ docker container ls
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES
602dbf1edc81        alpine              "ash"               4 seconds ago       Up 3 seconds                            alpine2
da33b7aa74b0        alpine              "ash"               17 seconds ago      Up 16 seconds                           alpine1
  1. See Network manage commands:
$ docker network --help
Manage Network Options:
Commands:
connect      Connect a container to a network
create       Create a Network
disconnect   Disconnect a container from a network
inspect      Display detailed information on one or more networks
ls           List networks
prune        Remove all unused networks
rm           Remove one or more networks
  1. Inspect the bridge network to see what containers are connected to it.
$ docker network inspect bridge

Also use it to find the IP address of the running container.

$ docker inspect "container ID"

To retrieve just the IP address of the running container:-

$ docker inspect -f '{{ .NetworkSettings.IPAddress }}' "container ID"

or

$ docker inspect <container id> | grep "IPAddress"
  1. The containers are running in the background. Use the docker attach command to connect to alpine2.
$ docker attach alpine2
/#

Now root user within alpine2 container.

  1. From within alpine2, ping bing.com and then ping first container(alpine1).
# ping -c 2 bing.com

# ping -c 172.17.0.2
  1. Detach from alpine1. Stop and remove both containers.
$ docker container stop alpine1 alpine2
$ docker container rm alpine1 alpine2

User-defined bridge network

  1. Create the my-alpine-net network
$ docker network create my-alpine-net
  1. List Docker’s networks:
$ docker network ls
NETWORK ID          NAME                DRIVER              SCOPE
17e324f45964        bridge              bridge              local
6ed54d316334        host                host                local
e9261a8c9a19       my-alpine-net        bridge              local
7092879f2cc8        none                null                local
  1. Create your three containers. First alpine container attached to user-defined network (my-alpine-net), second connected to bridge network only and third connected to both.
$ docker run -dit --name alpine1 --network my-alpine-net alpine ash
$ docker run -dit --name alpine2 alpine ash
$ docker run -dit --name alpine3 --network my-alpine-net alpine ash
$ docker network connect bridge alpine3
  1. After the containers are created and runnning, inspect the bridge network and the my-alpine-net network.
$ docker network inspect bridge
[
    {

        "Name": "bridge",
        "Id": "5b712f666694cbaefc55335e332b5250dfb96c97d920bf8bf83c9cfee9a85c8a",
        "Created": "2018-06-07T08:41:10.017839579Z",
        "Scope": "local",
        "Driver": "bridge",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": null,
            "Config": [
                {
                    "Subnet": "172.17.0.0/16"
                }
            ]
        },
        "Internal": false,
        "Attachable": false,
        "Ingress": false,
        "ConfigFrom": {
            "Network": ""
        },
        "ConfigOnly": false,
        "Containers": {
            "875ad3a4ad18b37bcdd9a483f7ee04d53482876f604bc002f4bb80993a224285": {
                "Name": "alpine2",
                "EndpointID": "42c94353e1133c6a1f177cbb8550dddb33a80eb18432ca35203a2384d1ab442e",
                "MacAddress": "02:42:ac:11:00:02",
                "IPv4Address": "172.17.0.2/16",
                "IPv6Address": ""
            },
            "e9d5c70b22843266ec4215f64a27878110aa4abcdce9f23f59945d2c56cf0d62": {
                "Name": "alpine3",
                "EndpointID": "df75f77ee9cdf83d7412a8985e3dbc6f8446f5de74196bb458f0a5a11a6831ac",
                "MacAddress": "02:42:ac:11:00:03",
                "IPv4Address": "172.17.0.3/16",
                "IPv6Address": ""
            }
        },
        "Options": {
            "com.docker.network.bridge.default_bridge": "true",
            "com.docker.network.bridge.enable_icc": "true",
            "com.docker.network.bridge.enable_ip_masquerade": "true",
            "com.docker.network.bridge.host_binding_ipv4": "0.0.0.0",
            "com.docker.network.bridge.name": "docker0",
            "com.docker.network.driver.mtu": "1500"
        },
        "Labels": {}
    }
]

Inspect my-network-netnetwork.

$ docker network inspect my-alpine-net
[
    {
        "Name": "my-alpine-net",
        "Id": "4bdbb2bc8ff1a9d7bba53dcffb604593d593c3ab218b999101627333eb4c756b",
        "Created": "2018-06-07T08:48:40.405847087Z",
        "Scope": "local",
        "Driver": "bridge",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": {},
            "Config": [
                {
                    "Subnet": "172.20.0.0/16",
                    "Gateway": "172.20.0.1"
                }
            ]
        },
        "Internal": false,
        "Attachable": false,
        "Ingress": false,
        "ConfigFrom": {
            "Network": ""
        },
        "ConfigOnly": false,
        "Containers": {
            "0005af800c2cfbe43fb09e0515767d5c6cf04240c7cbb1a00fac045979fefe42": {
                "Name": "alpine1",
                "EndpointID": "8dd17e2c1536c4c9a081aee0b8a315ea152eef09222e4d73e5e66ba786d0ab85",
                "MacAddress": "02:42:ac:14:00:02",
                "IPv4Address": "172.20.0.2/16",
                "IPv6Address": ""
            },
            "e9d5c70b22843266ec4215f64a27878110aa4abcdce9f23f59945d2c56cf0d62": {
                "Name": "alpine3",
                "EndpointID": "6e00792f2cc3affcb15c21ec12289ab6698f972abe43a61a608cbe9041f5f1b2",
                "MacAddress": "02:42:ac:14:00:03",
                "IPv4Address": "172.20.0.3/16",
                "IPv6Address": ""
            }
        },
        "Options": {},
        "Labels": {}
    }
]
  1. Create the my-alpine-net network
$ docker container attach alpine1

Now ping other Containers

/ # ping -c 2 alpine2
ping: bad address 'alpine2'
/ # ping -c 2 alpine 2
PING alpine3 (172.20.0.3): 56 data bytes
64 bytes from 172.20.0.3: seq=0 ttl=64 time=0.188 ms
64 bytes from 172.20.0.3: seq=1 ttl=64 time=0.092 ms
--- alpine3 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 0.092/0.140/0.188 ms
  1. Dettach from alpine1 and attach to alpine3(connected to both networks)
$ docker container attach alpine3
/ # ping -c 2 alpine1
PING alpine1 (172.20.0.2): 56 data bytes
64 bytes from 172.20.0.2: seq=0 ttl=64 time=0.115 ms
64 bytes from 172.20.0.2: seq=1 ttl=64 time=0.094 ms
--- alpine1 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 0.094/0.104/0.115 ms
/ # ping -c 2 alpine2
ping: bad address 'alpine2'

Can't ping alpine2(default bridge) using name. We need to address alpine2 by its IP address.

$ docker container attach alpine3
/ # ping -c 2 172.17.0.2
PING 172.17.0.2 (172.17.0.2): 56 data bytes
64 bytes from 172.17.0.2: seq=0 ttl=64 time=0.141 ms
64 bytes from 172.17.0.2: seq=1 ttl=64 time=0.075 ms
--- alpine1 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 0.075/0.108/0.141 ms
  1. Stop and remove all containers and the my-alpine-net network.
$ docker container stop alpine1 alpine2 alpine3
$ docker container rm alpine1 alpine2 alpine3
$ docker network rm my-alpine-net