docker-hosts-provider/monitor.py

#!/usr/bin/env python3

# dbus-1-devel glib2-devel

import docker
import time
import os
import logging
import ipaddress
from pathlib import Path
from collections import defaultdict

from xml.etree import ElementTree as ET

# Configure logging
logging.basicConfig(
    level=logging.INFO,
    format='%(asctime)s - %(levelname)s - %(message)s'
)

# Configuration
DOMAIN = os.environ.get("DOMAIN", "home.arpa")
HOSTS_FILE = "/etc/docker_hosts"
UPDATE_INTERVAL = 2 # seconds

# Define subnet to IP mapping structure
class SubnetBasedIPs:
    def __init__(self):
        self.networks = []  # List of (network, ip) tuples
    
    def add_ip(self, ip, subnet):
        try:
            network = ipaddress.ip_network(subnet, strict=False)
            self.networks.append((network, ip))
        except ValueError as e:
            logging.error(f"Invalid subnet {subnet} for IP {ip}: {e}")
    
    def get_best_ip(self, client_ip):
        try:
            client = ipaddress.ip_address(client_ip)
            for network, ip in self.networks:
                if client in network:
                    return ip
            # If no matching subnet found, return the first IP
            return self.networks[0][1] if self.networks else None
        except ValueError as e:
            logging.error(f"Invalid client IP {client_ip}: {e}")
            return self.networks[0][1] if self.networks else None

def get_macvlan_networks():
    """Get all Docker networks that use the macvlan driver."""
    client = docker.from_env()
    networks = client.networks.list()
    macvlan_networks = []
    
    for network in networks:
        if network.attrs.get('Driver') == 'macvlan':
            config = network.attrs.get('IPAM', {}).get('Config', [])
            for cfg in config:
                subnet = cfg.get('Subnet')
                if subnet:
                    macvlan_networks.append((network.name, subnet))
    
    return macvlan_networks

def get_container_ips():
    client = docker.from_env()
    container_ips = defaultdict(SubnetBasedIPs)
    macvlan_networks = get_macvlan_networks()
    
    if not macvlan_networks:
        logging.warning("No macvlan networks found!")
        return container_ips
    
    logging.info(f"Monitoring macvlan networks: {macvlan_networks}")
    
    # Create network name to subnet mapping
    network_subnets = {name: subnet for name, subnet in macvlan_networks}
    
    for container in client.containers.list():
        hostname = container.attrs['Config'].get('Hostname')
        container_name = container.name
        networks = container.attrs['NetworkSettings']['Networks']
        
        logging.debug(f"Checking container: {container_name} (hostname: {hostname})")
        
        for network_name, network_config in networks.items():
            if network_name in network_subnets:
                ip = network_config.get('IPAddress')
                subnet = network_subnets[network_name]
                
                logging.debug(f"Found IP for {network_name} ({subnet}): {ip}")
                
                if ip and container_name:
                    container_ips[f"{container_name}.{DOMAIN}"].add_ip(ip, subnet)
    return container_ips

def get_macvlan_networks():
    """Get all Docker networks that use the macvlan driver."""
    client = docker.from_env()
    networks = client.networks.list()
    macvlan_networks = []
    
    for network in networks:
        if network.attrs.get('Driver') == 'macvlan':
            config = network.attrs.get('IPAM', {}).get('Config', [])
            for cfg in config:
                subnet = cfg.get('Subnet')
                if subnet:
                    macvlan_networks.append((network.name, subnet))
                    logging.info(f"Found macvlan network: {network.name} with subnet: {subnet}")
    
    return macvlan_networks

def generate_hosts_entries(container_ips):
    """Generate all possible host entries for CoreDNS to use."""
    entries = []
    
    # Get all unique subnets from macvlan networks
    test_subnets = [subnet for _, subnet in get_macvlan_networks()]
    logging.info(f"Generated entries for subnets: {test_subnets}")
    
    for hostname, subnet_ips in container_ips.items():
        # Generate entries for each detected subnet
        for subnet in test_subnets:
            try:
                # Use a representative IP from each subnet for testing
                test_ip = str(next(ipaddress.ip_network(subnet).hosts()))
                best_ip = subnet_ips.get_best_ip(test_ip)
                if best_ip:
                    entries.append(f"{best_ip} {hostname}")
            except Exception as e:
                logging.error(f"Error generating entry for {hostname} subnet {subnet}: {e}")
    
    return entries

def update_hosts_file(container_ips):
    # Create hosts file content
    hosts_content = "# Auto-generated by docker-dns-monitor\n"
    hosts_content += "127.0.0.1 localhost\n\n"
    
    # Add entries for each subnet and remove duplicates
    entries = list(set(generate_hosts_entries(container_ips)))

    hosts_content += "\n".join(entries)
    
    logging.info("Writing hosts file with content:")
    logging.info(hosts_content)
    
    # Ensure directory exists
    os.makedirs(os.path.dirname(HOSTS_FILE), exist_ok=True)
    
    try:
        # Write to temporary file first
        temp_file = f"{HOSTS_FILE}.tmp"
        with open(HOSTS_FILE, 'w') as f:
            f.write(hosts_content)
        
        # Check file permissions
        # os.chmod(temp_file, 0o644)
        
        # Atomic replace
        # os.rename(temp_file, HOSTS_FILE)
        logging.info(f"Successfully updated {HOSTS_FILE}")
    except Exception as e:
        logging.error(f"Error writing hosts file: {e}")
        raise

def main():
    logging.info("Starting Docker DNS monitor...")
    # avahi_publisher = AvahiPublisher()
    while True:
        try:
            current_ips = get_container_ips()
            
            if current_ips:
                logging.info("Current DNS mappings:")
                for hostname, subnet_ips in sorted(current_ips.items()):
                    for network, ip in subnet_ips.networks:
                        logging.info(f"  {hostname} -> {ip} (subnet: {network})")
                    
                update_hosts_file(current_ips)
                # avahi_publisher.publish_hosts(current_ips)
            else:
                logging.warning("No containers found on macvlan networks.")
            
            time.sleep(UPDATE_INTERVAL)
            
        except Exception as e:
            logging.error(f"Error: {e}")
            time.sleep(UPDATE_INTERVAL)

if __name__ == "__main__":
    main()