hostdiscovery.py

# -*- coding: utf-8 -*-
#
# Retrieve a list of hosts from EC2, with Name metadata tags matching
# the supplied regex.
#
# e.g. in your fabfile
#
#     env.roledefs = {
#         'somesite': lambda: matching_names(r'somesite-web-\d+'),
#        }
#
import re

import boto.ec2


def matching_names(name_regex, region='ap-southeast-2',
                   public_dns_names=False):
    """Queries AWS EC2 for instances whose 'name' metadata matches
    the supplied regex.

    Note this depends on boto being able to authenticate with
    AWS. This is achieved by setting two environment variables:

        AWS_ACCESS_KEY_ID
        AWS_SECRET_ACCESS_KEY

    TODO: maybe more intelligently return hosts based on their
    “accessibility” status.
    """

    conn = boto.ec2.connect_to_region(region)

    # fetch instance ids whose 'name' tag matches the supplied regex
    instances = {}
    for tag in conn.get_all_tags():
        if tag.name == 'Name' and re.match(name_regex, tag.value):
            # store the 'name' tag's full value
            instances.update({tag.res_id: tag.value})

    if not instances:
        # no running instances 'name' tag matched the supplied regex,
        # so return an empty list
        return []
    else:
        # fetch addresses for the instances fetched earlier
        hostlist = []
        for ec2_i in conn.get_all_instances():
            if ec2_i.instances[0].id in instances.keys():
                hostlist.append(
                    public_dns_names and ec2_i.instances[0].public_dns_name \
                    or ec2_i.instances[0].private_dns_name)
        return hostlist