lambda function to replace AMI in launch config and apply to autoscaling group, keeping root volume information

update_asg

from __future__ import print_function
 
import json
import datetime
import time
import boto3
 
print('Loading function')
 
 
def lambda_handler(event, context):
    print("Received event: " + json.dumps(event, indent=2))
 
    # get autoscaling client
    client = boto3.client('autoscaling')
    clientEc2 = boto3.client('ec2')
 
    # get object for the ASG we're going to update, filter by name of target ASG
    response = client.describe_auto_scaling_groups(AutoScalingGroupNames=[event['targetASG']])
 
    if not response['AutoScalingGroups']:
        return 'No such ASG'
 
    # get name of InstanceID in current ASG that we'll use to model new Launch Configuration after
    sourceInstanceId = response.get('AutoScalingGroups')[0]['Instances'][0]['InstanceId']
     
    # get the snapshotID of the source AMI
    responseAmi = clientEc2.describe_images(ImageIds=[event['newAmiID']])
    sourceAmiSnapshot = responseAmi.get('Images')[0]['BlockDeviceMappings'][0]['Ebs']['SnapshotId']
    print('New source AMI: ' + event['newAmiID'] + " has snapshot ID: " + sourceAmiSnapshot)
     
    # get block device mapping (by default boto doesn't copy this)
    sourceLaunchConfig = response.get('AutoScalingGroups')[0]['LaunchConfigurationName']
    print('current launch config name:' + sourceLaunchConfig)
    responseLC = client.describe_launch_configurations(LaunchConfigurationNames=[sourceLaunchConfig])
    #print(responseLC)
    sourceBlockDevices = responseLC.get('LaunchConfigurations')[0]['BlockDeviceMappings']
    print('Current LC block devices:')
    print(sourceBlockDevices[0]['Ebs'])
    sourceBlockDevices[0]['Ebs']['SnapshotId'] = sourceAmiSnapshot
    print('New LC block devices (snapshotID changed):')
    print(sourceBlockDevices[0]['Ebs'])
 
    # create LC using instance from target ASG as a template, only diff is the name of the new LC and new AMI
    timeStamp = time.time()
    timeStampString = datetime.datetime.fromtimestamp(timeStamp).strftime('%Y-%m-%d-%H-%M-%S')
    newLaunchConfigName = event['targetASG'] + '_'+ event['newAmiID'] + '_' + timeStampString
    print('new launch config name: ' + newLaunchConfigName)
    client.create_launch_configuration(
        InstanceId = sourceInstanceId,
        LaunchConfigurationName=newLaunchConfigName,
        ImageId= event['newAmiID'],
        BlockDeviceMappings = sourceBlockDevices )
 
    # update ASG to use new LC
    response = client.update_auto_scaling_group(AutoScalingGroupName = event['targetASG'],LaunchConfigurationName = newLaunchConfigName)
 
    return 'Updated ASG `%s` with new launch configuration `%s` which includes AMI `%s`.' % (event['targetASG'], newLaunchConfigName, event['newAmiID'])