Docker - Network

About

This article is about the creation of a network (ie address space) between containers inside docker.

After the docker installation you have 3 networks type by default.

A container is created in the bridge betwork (docker0) network by default.

docker network ls

NETWORK ID          NAME                DRIVER              SCOPE
bb7eed89ed8f        bridge              bridge              local
c98218bf8e12        host                host                local
900385c9a1f0        none                null                local

Driver

built-in network drivers:bridge, overlay and macvlan.
plug-in network drivers

Bridge

The bridge driver creates a private network internal to the host so containers on this network can communicate.

If you want to access them from the outside you have to grant external access by (exposing|mapping) the ports. See port. It will map the port of your container to the port of your real server (the host network). After that accessing your server on 8080 will route to your bridge network on port 8080.

docker run -p 8080:8080

Everything in the bridge network is in the private range of “Subnet”: “172.17.0.0/16”

Full Example of a fictitious app comprised of a web and db container:

# Create a bridge
docker network create -d bridge mybridge
# Create a container named db (--name) with the myDBImage image on the mybridge network (--net) as a daemon (-d)
docker run -d --net mybridge --name db myDBImage
# Create a container named web (--name) with the myWebImage image on the mybridge network (--net) as a daemon (-d)
# set the environement varaible DB (-e) and open the container's port 5000 to the host as 8000 (-p)
docker run -d --net mybridge -e DB=db -p 8000:5000 --name web myWebImage

The bridge driver is a local scope driver, which means it only provides service discovery, IPAM, and connectivity on a single host. Multi-host service discovery requires an external solution that can map containers to their host location. This is where overlay drivers help.

Host

All containers in the host network are able to communicate with each other on the host interface. see Docker - Host Network

Compose

By default Compose sets up a single network for your app. Each container for a service joins the default network and is both reachable by other containers on that network, and discoverable by them at a hostname identical to the container name.

Network Mode

The app’s network is given as name: project name + _default

version 2.0

network_mode: "bridge"
network_mode: "host"
network_mode: "none"
network_mode: "service:[service name]"
network_mode: "container:[container name/id]"

where:

Network - Bridge Driver

Port

Networked service-to-service communication use the CONTAINER_PORT. When HOST_PORT is defined, the service is accessible outside as well.

services:
  db:
    image: postgres
    ports:
      - "8001:5432"

The connection string to db would look like:

within the web container, postgres://db:5432
within the host machine, postgres://{DOCKER_IP}:8001

Management

Command	Description
docker network connect	Connect a container to a network
docker network create	Create a network
docker network disconnect	Disconnect a container from a network
docker network inspect	Display detailed information on one or more networks
docker network ls	List networks
docker network prune	Remove all unused networks
docker network rm	Remove one or more networks

Create

A network is created on the host.

network create

docker network create [OPTIONS] NETWORK

List

All

docker network ls

NETWORK ID          NAME                DRIVER              SCOPE
38a952454ba6        bridge              bridge              local
af83ed7a2409        dockerelk_elk       bridge              local
c11d9bd528c9        host                host                local
d06e4bcb5131        none                null                local

One

docker network inspect bridge

[
    {
        "Name": "bridge",
        "Id": "38a952454ba65f5448f4d796ca5c638c32d67f35ee68fb9df521e7c51dd003b4",
        "Scope": "local",
        "Driver": "bridge",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": null,
            "Config": [
                {
                    "Subnet": "172.17.0.0/16",
                    "Gateway": "172.17.0.1"
                }
            ]
        },
        "Internal": false,
        "Containers": {},
        "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": {}
    }
]