elastic_ip.py

#!/usr/bin/env python

import time
import os
from boto import utils, connect_ec2

ELASTIC_IPS = os.environ['ELASTIC_IPS'].split(', ')
NUMBER_OF_TRIES = 5

metadata = utils.get_instance_metadata()
instance_id = metadata['instance-id']
connection = connect_ec2()
connection.get_all_instances(instance_ids=instance_id)[0].instances[0]

addresses = connection.get_all_addresses(addresses=ELASTIC_IPS)
for address in addresses:
    if instance_id == address.instance_id:
        print "Instance already associated with EIP {}.".format(address.public_ip)
        exit(0)

for attempt in range(NUMBER_OF_TRIES):
    """
    Try multiple times to associate each unused address from the list. Do
    this incase multiple nodes try to use the same address at the same time.
    """
    if attempt != 0:
        print "Waiting 2 seconds before trying again..."
        time.sleep(2)

    unused_addresses = [a for a in addresses if not a.instance_id]
    if not unused_addresses:
        print "No unused EIP's found. Are there enough EIPs for the ASG?"
        continue

    for address in unused_addresses:
        try:
            print "Associating EIP {}".format(address.public_ip)
            connection.associate_address(instance_id=instance_id, public_ip=None, allocation_id=address.allocation_id)
        except Exception as e:
            print "Failed to associate EIP {}. Error was:\n{}".format(address.public_ip, e)
            continue
        else:
            print "Successfully associated EIP {}.".format(address.public_ip)
            exit(0)

print "Failed to associate any EIP after {} tries".format(NUMBER_OF_TRIES)
exit(1)