Discover ec2 instances by tag and tag value

ec2-discover-instances.py

from boto import ec2

class Resource(object):
    """
    Represents a single resource returned from the Discovery class's
    get_resources method.
    """
    def __init__(self, host_name, private_host_name, ip, private_ip, tags):
        self.__host_name = host_name
        self.__private_host_name = private_host_name
        self.__ip = ip
        self.__private_ip = private_ip
        self.__tags = tags

    @property
    def host_name(self):
        return self.__host_name

    @property
    def private_host_name(self):
        return self.__private_host_name

    @property
    def ip(self):
        return self.__ip

    @property
    def private_ip(self):
        return self.__private_ip

    @property
    def tags(self):
        return self.__tags


class Discovery(object):
    def __init__(self, region):
        self.__ec2conn = None
        self.__ec2conn = ec2.connect_to_region(region, 
            aws_access_key_id="<An AWS access key>", 
            aws_secret_access_key="<An AWS secret key>")
        if self.__ec2conn is None:
            raise Exception("ec2 discovery: connection to region {} failed.".format(region))

    def get_resources(self, tag=None, tag_value=None):
        """
        Returns the list of all running resources tagged with the named tag 
        having the passed value. If the value is None all running resources having
        the tag are returned. If tag is None all running resources are returned.
        """
        result = []
        reservations = self.__ec2conn.get_all_instances()
        for res in reservations:
            for inst in res.instances:
                if inst.state != 'running':
                    continue
                if tag is None:
                    result.append(inst)
                    continue
                if tag not in inst.tags:
                    continue
                if tag_value is None:
                    result.append(inst)
                    continue
                if inst.tags[tag].lower() == tag_value.lower():
                     result.append(inst)

        for i in range(0, len(result)):
            inst = result[i]
            tags = dict()
            for tag in inst.tags:
                tags[tag] = inst.tags[tag]
            resource = Resource(inst.dns_name, inst.private_dns_name,
                inst.ip_address, inst.private_ip_address, tags)
            result[i] = resource
        return result