Find IDs of containers that we can network to.

docker-reachable-containers.py

# -*- coding: utf-8 -*-


import docker
import os
import re


def readfile(path):
    """Read a UTF-8 encoded text file from disk."""

    with open(path, 'rb') as stream:
        return stream.read().decode('utf-8')


def container_id():
    """Find the ID of the current container."""

    # TODO: switch to the "CID file" when the compose file syntax supports it.
    mountinfo = readfile('/proc/self/mountinfo')
    mountinfo = [line.strip() for line in mountinfo.split('\n')]
    for line in mountinfo:
        match = re.search(r'/docker/(\w{64})\s+', line)
        if match:
            return match.group(1)
    raise ValueError('Could not detect container ID!')


def reachable_networks(container_id):
    """Find the IDs of networks the container is attached to."""

    # We need to use the low-level API because the "high-level" API doesn't
    # allow us to query the networks accessible to a container.
    client = docker.APIClient(
        base_url='unix://var/run/docker.sock',
        version=os.environ.get('DOCKER_API_VERSION', 'auto'),
    )
    container = client.inspect_container(container_id)
    return set(
        network['NetworkID']
        for network in container['NetworkSettings']['Networks'].values()
    )


container = container_id()
print('Container ID:', container)
print('Network IDs:', sorted(reachable_networks(container)))

client = docker.from_env(
    version=os.environ.get('DOCKER_API_VERSION', 'auto')
)

# Locate all containers in our networks.
reachable_containers = {}
for network_id in reachable_networks(container):
    network = client.networks.get(network_id)
    for container in network.containers:
        reachable_containers[container.id] = container

print('Reachable containers:', reachable_containers.keys())