gross hackage to find an available subnet for docker-compose and smash it into the yaml

docker_compose_fixnet.py

#!/usr/bin/env python3

import yaml
import docopt
import sh
import json

BLACKLIST = [24, 25, 26]
SKIP = ["host", "none"]


class UnsupportedComposeFormat(Exception):
    """Only v2 and v3 docker-compose yaml formats allow us to change the subnetwork"""


class NoNetworksAvailable(Exception):
    """We ran out of potential networks"""


def docker_find_pool():
    """Find an available subnet for this docker-compose networking fubar."""
    taken = set()
    networks = sh.docker.network.list()

    for network in networks.split("\n")[1:-1]:
        network_id, name, driver, scope = network.split()
        if name in SKIP:
            continue

        network_config = sh.docker.network.inspect("-f", "{{json .IPAM.Config}}", name).stdout
        print(name, network_config)
        parsed = json.loads(network_config.decode("UTF-8"))

        if len(parsed) > 0:
            taken.add(int(parsed[0]['Subnet'].split('.')[1]))
        # else:
        #     print("Skipping %s" % parsed)

    for net in range(17, 255):
        if net in BLACKLIST or net in taken:
            continue
        else:
            return "172.%i.0.0/16" % net

    raise NoNetworksAvailable


def docker_compose_fixnet():
    """
    Cleanup docker compose networking to avoid internal 172.x networks.

    Usage:
      docker-compose-fixnet [DOCKER-COMPOSE-FILE]

    Options:
        DOCKER-COMPOSE-FILE     Defaults to docker-compose.yml
    """
    args = docopt.docopt(docker_compose_fixnet.__doc__)
    compose_fn = args.get("DOCKER-COMPOSE-FILE")
    if compose_fn is None:
        compose_fn = "docker-compose.yml"

    with open(compose_fn, 'r') as h:
        compose_file = yaml.load(h)

        new_subnet = docker_find_pool()
        print("Allocating %s" % new_subnet)
        # v1 or v2?
        if compose_file.get('version', "1") == "1":
            raise UnsupportedComposeFormat(
                "Only docker-compose.yml v2 and v3 are supported"
            )
        elif compose_file.get('version') == "2":
            compose_file["networks"] = {
                "default": {
                    "driver": "default",
                    "ipam": {
                        "driver": "default",
                        "config": {
                            "subnet": new_subnet
                        }
                    }
                }
            }
        elif compose_file.get('version') == "3":
            compose_file["networks"] = {
                "default": {
                    "driver": "default",
                    "ipam": {
                        "driver": "default",
                        "config": {
                            "subnet": new_subnet
                        }
                    }
                }
            }

    with open(compose_fn, 'w') as h:
        yaml.dump(compose_file, h, default_flow_style=False)


docker_compose_fixnet()