hosts.py A script for retrieving AWS EC2 instance information in a format usable for your /etc/hosts file. Poor man's DNS, anyone? Requires installation of the package 'boto' (pip install boto) and the creation of a ~/.boto configuration file explained here: http://docs.pythonboto.org/en/latest/boto_config_tut.html

hosts.py

#!/usr/bin/env python

"""
Usage: hosts.py [options]

Options:
      -h, --help            show this help message and exit
        -r REGION, --region=REGION
                                Region (default us-east-1)
"""
import sys
from operator import attrgetter
from optparse import OptionParser

try:
    import boto
except ImportError:
    sys.stderr.write("Boto required.  Please 'pip install boto'\n")
    sys.exit(1)

from boto.ec2 import regions


HEADERS = {
    'ID': {'get': attrgetter('id'), 'length':15},
    'Zone': {'get': attrgetter('placement'), 'length':15},
    'Groups': {'get': attrgetter('groups'), 'length':30},
    'Hostname': {'get': attrgetter('public_dns_name'), 'length':50},
    'PrivateHostname': {'get': attrgetter('private_dns_name'), 'length':50},
    'State': {'get': attrgetter('state'), 'length':15},
    'Image': {'get': attrgetter('image_id'), 'length':15},
    'Type': {'get': attrgetter('instance_type'), 'length':15},
    'IP': {'get': attrgetter('ip_address'), 'length':16},
    'PrivateIP': {'get': attrgetter('private_ip_address'), 'length':16},
    'Key': {'get': attrgetter('key_name'), 'length':25},
    'T:': {'length': 30},
}

def get_column(name, instance=None):
    if name.startswith('T:'):
        _, tag = name.split(':', 1)
        return instance.tags.get(tag, '')
    return HEADERS[name]['get'](instance)


def main():
    parser = OptionParser()
    parser.add_option("-r", "--region", help="Region (default us-east-1)", dest="region", default="us-east-1")
    (options, args) = parser.parse_args()


    # Connect the region
    for r in regions():
        if r.name == options.region:
            region = r
            break
    else:
        print "Region %s not found." % options.region
        sys.exit(1)
    ec2 = boto.connect_ec2(region=region)

    headers = ("IP", "T:Name")

    # Create format string
    format_string = ""
    for h in headers:
        if h.startswith('T:'):
            format_string += "%%-%ds" % HEADERS['T:']['length']
        else:
            format_string += "%%-%ds" % HEADERS[h]['length']


    filters = {'instance-state-name': 'running'}

    # List and print
    for r in ec2.get_all_instances(filters=filters):
        groups = [g.name for g in r.groups]
        for i in r.instances:
            i.groups = ','.join(groups)
            print " ".join(tuple(get_column(h, i) for h in headers))


if __name__ == "__main__":
    main()