Generate Marathon JSON from Docker images.

docker2marathon.py

"""Generate Marathon JSON from Docker images.

Usage:
  docker2marathon.py [options] <image>
  docker2marathon.py (-h | --help)

Options:
  --cpus=<shares>   CPU shares for this app [default: 0.5]
  --mem=<megabytes> MB of memory for this app [default: 256]
"""
import sys
import subprocess
import codecs
import json
from docopt import docopt

def exec_command(cmd, env=None, stdin=None):
    """Execute CLI command

    :param cmd: Program and arguments
    :type cmd: [str]
    :param env: Environment variables
    :type env: dict
    :param stdin: File to use for stdin
    :type stdin: file
    :returns: A tuple with the returncode, stdout and stderr
    :rtype: (int, bytes, bytes)
    """

    process = subprocess.Popen(
        cmd,
        stdin=stdin,
        stdout=subprocess.PIPE,
        stderr=subprocess.PIPE,
        env=env)

    # This is needed to get rid of '\r' from Windows's lines endings.
    stdout, stderr = [std_stream.replace(b'\r', b'')
                      for std_stream in process.communicate()]

    return (process.returncode, stdout, stderr)


args = docopt(__doc__, version='0.0.1')

image = args["<image>"]
cpus = float(args["--cpus"])
mem = int(args["--mem"])

print("Pulling Docker image {}".format(image), file=sys.stderr)
exec_command(["docker", "pull", image])

print("Inspecting Docker image {}".format(image), file=sys.stderr)
code, stdout, stderr = exec_command(["docker", "inspect", image])

image_json = json.loads(stdout.decode(encoding='UTF-8'))

portMappings = [{"containerPort": int(k.split("/")[0]), "protocol": k.split("/")[1], "hostPort": 0} for (k, v) in image_json[0]["Config"]["ExposedPorts"].items()]
healthChecks = [{"protocol": "TCP", "portIndex": i} for i, portMap in enumerate(portMappings)]

appId = image.split(":")[0]

marathon_json = {
  "id": appId,
  "instances": 1,
  "cpus": cpus,
  "mem": mem,
  "container": {
    "type": "DOCKER",
    "docker": {
      "image": image,
      "network": "BRIDGE",
      "portMappings": portMappings
    }
  },
  "healthChecks": healthChecks
}

print(json.dumps(marathon_json))