Script to list service ports and get next available port

docker-service-ports

#!/usr/bin/env python3.6
import argparse
import logging
import re
import shlex

import sh

PORT_RE = re.compile(r':(?P<port>\d+)->')

MIN_PORT = 1024


def get_next_port(used_ports):
    next_port = MIN_PORT
    while next_port < 65536:
        if next_port not in used_ports:
            break

    return next_port


def get_services():
    command = "docker service ls --format '{{ .Name }} {{ .Ports }}'"
    command_split = shlex.split(command)

    proc = sh.docker(*command_split[1:])
    for line in proc.stdout.decode('utf8').splitlines():
        line = line.strip()
        if line == '':
            continue

        if ' ' not in line:
            continue

        yield line


def get_used_ports():
    ports = []
    for line in get_services():
        line_split = line.split(' ', 1)
        if len(line_split) < 2:
            continue

        _ports = line_split[-1]
        for matches in PORT_RE.finditer(_ports):
            ports.append(int(matches.group('port')))

    return sorted(ports)


def main():
    parser = argparse.ArgumentParser()
    parser.add_argument('--loglevel', '-l', default='warn', help='set logging level; default warn')
    parser.add_argument('--next', action='store_true', help='returns the next port')

    args = parser.parse_args()

    logging.basicConfig(level=getattr(logging, args.loglevel.upper()))

    logger = logging.getLogger('main')

    if args.next:
        used_ports = get_used_ports()
        next_port = get_next_port(used_ports)

        logger.info(f'used_ports={used_ports}')

        print(next_port)
    else:
        for line in get_services():
            print(line)


if __name__ == '__main__':
    main()