daemon.json.j2

{
  "bridge": "lxdbr0"
}

layer_docker_testing.py

from os.path import exists
from os import remove

from charms.reactive import when, when_not, set_state

from charmhelpers.core.templating import render
from charmhelpers.core.hookenv import status_set


@when('docker.ready')
@when_not('docker.daemon.json.available')
def seed_docker_daemon_network_config():

    status_set('maintenance', "Writing docker network config")
    docker_daemon_json = "/etc/docker/daemon.json"

    if exists(docker_daemon_json):
        remove(docker_daemon_json)

    render(source='daemon.json.j2', target=docker_daemon_json, context={})

    set_state('docker.daemon.json.available')
    status_set('active', "Docker networking in place")