Print out IP addresses to all juju units in the format of /etc/hosts

juju-network.py

#!/usr/bin/env python3

# Print out IP addresses to all juju units in the format of /etc/hosts

import yaml
from typing import Set, Tuple
import os
import subprocess
import sys


def stderr(*args, **kwargs):
    # https://stackoverflow.com/a/14981125/3516684
    print(*args, file=sys.stderr, **kwargs)


def main():
    with open(os.path.expanduser("~/.local/share/juju/models.yaml"), "rt") as f:
        models_file = f.read()
    
    ctrl_mdl: Set[Tuple[str, str]] = set()

    # It is called a models file, but the root keys are controllers
    controllers = yaml.safe_load(models_file)
    controllers = controllers["controllers"]

    for controller_name in controllers:
        models = controllers[controller_name]["models"]
        for model_name in models:
            ctrl_mdl.add((controller_name, model_name))

    stderr(ctrl_mdl)

    hosts: Set[Tuple[str, str]] = set()  # (address, dns_name)

    for controller_name, model_name in ctrl_mdl:
        stderr(f"Obtaining status for {controller_name}:{model_name}")
        cmd = f"juju status -m {controller_name}:{model_name} --format=yaml".split(" ")
        try:
            output = subprocess.check_output(cmd, stderr=subprocess.STDOUT, timeout=5)
        except (subprocess.CalledProcessError, subprocess.TimeoutExpired):
            stderr("Failed")
        else:
            status = yaml.safe_load(output)
            model_name = status["model"]["name"]
            apps = status["applications"]
            for app_name in apps:
                app = apps[app_name]
                if "address" not in app:
                    # This happens for "controller" models
                    stderr(f"No addresses for app '{app_name}'")
                    continue

                hosts.add((app["address"], f"{app_name}.{model_name}.juju.internal"))

                units = app["units"]
                for unit_name in units:
                    unit = units[unit_name]
                    address = unit["address"]
                    unit_id = unit_name.rsplit("/", 1)[-1]
                    hosts.add((address, f"unit-{unit_id}.{app_name}.{model_name}.juju.internal"))

                    if unit["leader"]:
                        hosts.add((address, f"leader.{app_name}.{model_name}.juju.internal"))

    for address, dns_name in hosts:
        print(address, dns_name)


if __name__ == "__main__":
    main()