gistfile1.py

#!/usr/bin/env python

import os
import shutil
import socket
from optparse import OptionParser

from boto import ec2

BASE = """
127.0.0.1 localhost %s

# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts
"""

def main(options, hostname):
    if not (options.aws_secret_key and options.aws_access_key):
        return

    os.environ['AWS_ACCESS_KEY_ID'] = options.aws_access_key
    os.environ['AWS_SECRET_ACCESS_KEY'] = options.aws_secret_key

    conn = ec2.connect_to_region(region_name="us-west-1")
    all_tags = conn.get_all_tags(filters={"tag:dns": "*"})

    new_lines = [BASE % hostname]

    for tag in all_tags:
        instance = conn.get_all_instances([tag.res_id])[0].instances[0]

        for dns_name in tag.value.strip().split(","):
            if instance.state == "running":
                new_lines.append(
                    "%s %s.internal %s" % (
                        socket.gethostbyname(instance.public_dns_name),
                        dns_name,
                        dns_name)
                    )

    f = open('/etc/hosts.new', 'wb')
    f.write("\n".join(new_lines))
    f.write("\n")
    f.flush()
    f.close()
    shutil.move('/etc/hosts.new', '/etc/hosts')

if __name__ == '__main__':
    """
    e.g, update_hosts.py --secret=<SECRET_KEY> --api=<API_KEY>
    """
    usage = "usage: %prog [options]"
    parser = OptionParser(usage=usage)

    parser.add_option("--secret", action="store", dest="aws_secret_key",
                        default=os.environ.get('AWS_SECRET_ACCESS_KEY'), help="AWS Secret Access Key")
    parser.add_option("--api", action="store", dest="aws_access_key",
                        default=os.environ.get('AWS_ACCESS_KEY_ID'), help="AWS Access Key")
    
    (options, args) = parser.parse_args()

    if len(args) != 1:
        raise Exception("Must know who we are in order to work")
    
    main(options, args[0])