#!/usr/bin/python

import boto.utils
import boto.ec2
import boto.vpc
import sys

dry_run = False

# AWS access/secret keys
aws_access      = None
aws_secret      = None

# Get all of the instance info e.g. curl 169.254.169.254/latest/meta-data/
try:
    instance_info = boto.utils.get_instance_metadata()
except:
    print "Could not get EC2 instance ID!"
    sys.exit(1)

instance_id = instance_info['instance-id']
region_name = instance_info['placement']['availability-zone'][:-1]
vpc_id      = instance_info['network']['interfaces']['macs'][instance_info['mac']]['vpc-id']

vpc_conn = boto.vpc.connect_to_region(region_name, aws_access_key_id=aws_access, aws_secret_access_key=aws_secret)
ec2_conn = boto.ec2.connect_to_region(region_name, aws_access_key_id=aws_access, aws_secret_access_key=aws_secret)

# Turn off Source/Destination checking if it's on
source_dest_check = ec2_conn.get_instance_attribute(instance_id, 'sourceDestCheck')['sourceDestCheck']
print "Source/Dest check: %s" % (source_dest_check,)

if source_dest_check:
    print "Instance must have source/dest checking disabled to NAT properly!"
    try:
        ec2_conn.modify_instance_attribute(instance_id, 'sourceDestCheck', False, dry_run=dry_run)
    except Exception, e:
        print "Could not modify source/dest check: %s" % (e,)
        sys.exit(1)

# Get the managed route tables for my VPC
rt = vpc_conn.get_all_route_tables(filters={'vpc_id':vpc_id,'tag:managed':'yes'})

# Just in case there's more than one
for table in rt:
    # See if there's a default route (0.0.0.0/0)
    gw_route = next((route for route in table.routes if route.destination_cidr_block == '0.0.0.0/0'), None)
    if not gw_route:
        print "Could not find default gw route in routing table!"
    else:
        print "Found a gateway route: %s, %s, %s" % (table.id, gw_route.destination_cidr_block, instance_id)
        try:
            # If there is delete it, because I'm taking it over
            vpc_conn.delete_route(table.id, '0.0.0.0/0', dry_run=dry_run)
        except Exception, e:
            print "Could not delete gw route! %s" % (e,)
            sys.exit(1)
    try:
        # Make me the default route, I'm the router now!
        vpc_conn.create_route(table.id, '0.0.0.0/0', instance_id=instance_id, dry_run=dry_run)
    except Exception, e:
        print "Could not replace gw route! %s" % (e,)
        sys.exit(1)