Script to dynamically grab public DNS names from an EC2 autoscale instances

ec2-autoscale-instances.py

#!/usr/bin/env python

"""
ec2-autoscale-instance.py

Read Autoscale DNS from AWS

Sample config file,
{
    "access_key": "key",
    "secret_key": "key",
    "group_name": "groupName"
}
"""

from __future__ import print_function
import argparse
import boto.ec2.autoscale
try:
    import simplejson as json
except ImportError:
    import json

CONFIG_ACCESS_KEY = 'access_key'
CONFIG_SECRET_KEY = 'secret_key'
CONFIG_GROUP_NAME = 'group_name'


def main():
    arg_parser = argparse.ArgumentParser(description=
                                         'Read Autoscale DNS names from AWS')
    arg_parser.add_argument('-c', dest='config_file',
                            help='JSON configuration file containing ' +
                                 'access_key, secret_key, and group_name')
    args = arg_parser.parse_args()
    config = json.loads(open(args.config_file).read())
    access_key = config[CONFIG_ACCESS_KEY]
    secret_key = config[CONFIG_SECRET_KEY]
    group_name = config[CONFIG_GROUP_NAME]

    ec2_conn = boto.connect_ec2(access_key, secret_key)
    as_conn = boto.connect_autoscale(access_key, secret_key)

    try:
        group = as_conn.get_all_groups([group_name])[0]
        instances_ids = [i.instance_id for i in group.instances]
        reservations = ec2_conn.get_all_reservations(instances_ids)
        instances = [i for r in reservations for i in r.instances]
        dns_names = [i.public_dns_name for i in instances]
        print('\n'.join(dns_names))
    finally:
        ec2_conn.close()
        as_conn.close()


if __name__ == '__main__':
    main()

Looks pretty useful, nice job

Could be improved to read instance profile credentials (when called from the AWS cloud), always best not to keep too many secrets.json files hanging around in the filesystem

Agreed. There is a standard location on systems that have those credentials, just didn't know about when I wrote this. Feel free to submit a PR if you switch it over.