#!/usr/bin/python

# Usage :
# aws ec2 describe-instances --filter="Name=instance-state-name,Values=running" | aws-instances-lookup <tag name> <tag value>

import sys
import json

def get_tag(instance, tag_key):
    for tag in instance['Tags']:
        if tag['Key'] == tag_key:
            print tag['Value']

tag_key = sys.argv[1]
tag_value = sys.argv[2]

instances_id = []
instances_name = []
output = json.load(sys.stdin)

reservations = output["Reservations"]

for reservation in reservations:
    instance = reservation['Instances'][0]
    for tag in instance['Tags']:
        if tag['Key'] == tag_key:
            if tag['Value'] == tag_value:
                instances_id.append(str(instance['InstanceId']))
                get_tag(instance, 'Name')