nginx_dns_reload.py

#!/usr/bin/python
import logging
import os
import os.path
import socket
import simplejson as json
import subprocess

#
##
### parameters - to do: include from external config file
aws_upstream = '[UPSTREAM_URL]'
json_dns_file = '/tmp/dns_check.json'
logfile = '/var/log/lb_dns_check.log'

#
##
### log config
logger = logging.getLogger(__name__)
logger.setLevel(logging.INFO)

handler = logging.FileHandler(logfile)
handler.setLevel(logging.INFO)

formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
handler.setFormatter(formatter)

logger.addHandler(handler)


def resolve(host_to_res):
    dns_res = socket.gethostbyname_ex(host_to_res)
    return dns_res


def write_json(json_file, data):
    with open(json_file, 'w+') as outfile:
        json.dump(data, outfile)


def read_json(json_file):
    with open(json_file, 'r') as infile:
        data = json.load(infile)
    return data


def check_exist(file_variable):
    if os.path.isfile(file_variable):
        print 'OK'
    else:
        logger.warn('creating file {}'.format(file_variable))
        current = resolve(aws_upstream)
        write_json(file_variable, current)


def restart_service(name):
    command = ['service', name, 'restart']
    # shell=FALSE for sudo to work.
    subprocess.call(command, shell=False)


def comp(list1, list2):
    a = list1[2]
    b = list2[2]
    a.sort()
    b.sort()
    return a == b


def main():
    check_exist(json_dns_file)
    current = resolve(aws_upstream)
    old = read_json(json_dns_file)
    if comp(old, current):
        logger.info('Dns has not changed : {}'.format(current[2]))
    else:
        logger.warn('Nginx is cactus - restarting')
        restart_service('nginx')
        write_json(json_dns_file,current)


if __name__ == '__main__':
    main()