hoster.py

#!/usr/bin/python3
import docker
import argparse
import shutil
import signal
import time
import sys
import os

label_name = "hoster.domains"
enclosing_pattern = "#-----------Docker-Hoster-Domains----------\n"
hosts_path = "/tmp/hosts"
hosts = {}

def signal_handler(signal, frame):
    global hosts
    hosts = {}
    update_hosts_file()
    sys.exit(0)

def main():
    # register the exit signals
    signal.signal(signal.SIGINT, signal_handler)
    signal.signal(signal.SIGTERM, signal_handler)

    args = parse_args()
    global hosts_path
    hosts_path = args.file

    dockerClient = docker.APIClient(base_url='unix://%s' % args.socket)
    events = dockerClient.events(decode=True)
    #get running containers
    for c in dockerClient.containers(quiet=True, all=False):
        container_id = c["Id"]
        container = get_container_data(dockerClient, container_id)
        hosts[container_id] = container

    update_hosts_file()

    #listen for events to keep the hosts file updated
    for e in events:
        if e["Type"]!="container": 
            continue
        
        status = e["status"]
        if status =="start":
            container_id = e["id"]
            container = get_container_data(dockerClient, container_id)
            hosts[container_id] = container
            update_hosts_file()

        if status=="stop" or status=="die" or status=="destroy":
            container_id = e["id"]
            if container_id in hosts:
                hosts.pop(container_id)
                update_hosts_file()


def get_container_data(dockerClient, container_id):
    #extract all the info with the docker api
    info = dockerClient.inspect_container(container_id)
    container_hostname = info["Config"]["Hostname"]
    container_name = info["Name"].strip("/")
    container_ip = info["NetworkSettings"]["IPAddress"]
    if info["Config"]["Domainname"]:
        container_hostname = container_hostname + "." + info["Config"]["Domainname"]
    
    result = []

    for values in info["NetworkSettings"]["Networks"].values():
        if not values["Aliases"]: 
            continue

        result.append({
                "ip": values["IPAddress"] , 
                "name": container_name,
                "domains": [container_name, container_hostname]
            })

    if container_ip:
        result.append({"ip": container_ip, "name": container_name, "domains": [container_name, container_hostname]})

    return result


def update_hosts_file():
    if len(hosts)==0:
        print("Removing all hosts before exit...")
    else:
        print("Updating hosts file with:")

    for id,addresses in hosts.items():
        for addr in addresses:
            print("ip: %s domains: %s" % (addr["ip"], addr["domains"]))

    #read all the lines of thge original file
    lines = []
    with open(hosts_path,"r+") as hosts_file:
        lines = hosts_file.readlines()

    #remove all the lines after the known pattern
    for i,line in enumerate(lines):
        if line==enclosing_pattern:
            lines = lines[:i]
            break;

    #remove all the trailing newlines on the line list
    if lines:
        while lines[-1].strip()=="": lines.pop()

    #append all the domain lines
    if len(hosts)>0:
        lines.append("\n\n"+enclosing_pattern)
        
        for id, addresses in hosts.items():
            for addr in addresses:
                lines.append("%s    %s\n"%(addr["ip"],"   ".join(addr["domains"])))
        
        lines.append("#-----Do-not-add-hosts-after-this-line-----\n\n")

    #write it on the auxiliar file
    aux_file_path = hosts_path+".aux"
    with open(aux_file_path,"w") as aux_hosts:
        aux_hosts.writelines(lines)

    #replace etc/hosts with aux file, making it atomic
    shutil.move(aux_file_path, hosts_path)
    
    post_update_exec()


def post_update_exec():
    sock = parse_args().socket
    cont_name = os.environ['POST_UPDATE_CONT']
    cont_cmd = os.environ['POST_UPDATE_CMD']
    
    if len(cont_name)>0 and len(cont_cmd)>0:
        print('POST_UPDATE_EXEC: running cmd "%s" in container "%s"' % (cont_cmd, cont_name))
        client = docker.DockerClient(base_url='unix://%s' % sock)
        try:
            container = client.containers.get(cont_name)
        except docker.errors.NotFound:
            print('[Error] POST_UPDATE_EXEC: container "%s" not found' % cont_name)
        else:
            result = container.exec_run(cont_cmd)
            if result.exit_code>0:
                print('[Error] POST_UPDATE_EXEC: command returned error %s: %s' % (result.exit_code, result.output))
        

def parse_args():
    parser = argparse.ArgumentParser(description='Synchronize running docker container IPs with host /etc/hosts file.')
    parser.add_argument('socket', type=str, nargs="?", default="tmp/docker.sock", help='The docker socket to listen for docker events.')
    parser.add_argument('file', type=str, nargs="?", default="/tmp/hosts", help='The /etc/hosts file to sync the containers with.')
    return parser.parse_args()

if __name__ == '__main__':
    main()