Script to upgrade autoscaling group

asg-ecs-rolling-upgrade.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import boto3
from multiprocessing.dummy import Pool as ThreadPool
import sys
import time

group_name = sys.argv[1]
ag = boto3.client('autoscaling')


def terminate_instance(instance, repeat=60):
    """ Repeat terminating call N times """
    if repeat == 0:
        print('Maximum waiting time exceeded for {0}'.format(instance))
        return
    else:
        try:
            response = ag.terminate_instance_in_auto_scaling_group(
                    InstanceId=instance,
                    ShouldDecrementDesiredCapacity=False)
        except Exception:
            return
        if response['Activity']['StatusCode'] != 'Successful':
            print('Termintating {0}, status {1}'.format(
                instance, response['Activity']['StatusCode']))
            print('Sleeping 10s, round {0}, instance {1}'.format(repeat, instance))
            repeat -= 1
            time.sleep(10)
            terminate_instance(instance, repeat)
        else:
            return


# Find attached launch configuration
try:
    ag_data = ag.describe_auto_scaling_groups(
            AutoScalingGroupNames=[group_name]
        )['AutoScalingGroups'][0]
except IndexError:
    print('AG {0} not found'.format(group_name))
    sys.exit(1)
lauch_config = ag_data['LaunchConfigurationName']
print('AG {0} has launch configuration {1}'.format(group_name, lauch_config))
instance_ids = [i['InstanceId'] for i in ag_data['Instances']]
# Find instances with wrong launch configuration
instance_data = ag.describe_auto_scaling_instances(
        InstanceIds=instance_ids,
        MaxRecords=50
    )['AutoScalingInstances']
to_replace = []
for i in instance_data:
    try:
        if i['LaunchConfigurationName'] != lauch_config:
            print('{0} changes from {1}'.format(i['LaunchConfigurationName']))
            print('{0} will be replaced'.format(i['InstanceId']))
            to_replace.append(i['InstanceId'])
    except KeyError:
        print('{0} will be replaced'.format(i['InstanceId']))
        to_replace.append(i['InstanceId'])
print('Totally {0} instances will be replaced'.format(len(to_replace)))
# terminate instances one by one, TODO implement batches
threadPool = ThreadPool(processes=2)
threadPool.map(terminate_instance, to_replace)
threadPool.close()
threadPool.join()