AWS Auto Scaling with boto

gistfile1.py

import boto
from boto.ec2.autoscale import ScalingPolicy
from boto.ec2.cloudwatch import MetricAlarm

autoscale = boto.connect_autoscale()
cloudwatch = boto.connect_cloudwatch()

# Let's assume you already have an Auto Scaling group.
# Setting one up is well documented elsewhere.
autoscaling_group = 'as_group_0'

# Define some Scaling Policies. These tell Auto Scaling _how_ to scale
# group, but not when to do it. (We'll define that later).

# We need one policy for scaling up...
scale_up_policy = ScalingPolicy(
    name='scale_up', adjustment_type='ChangeInCapacity',
    as_name=autoscaling_group, scaling_adjustment=1, cooldown=180)

#...and one for scaling down again.
scale_down_policy = ScalingPolicy(
    name='scale_down', adjustment_type='ChangeInCapacity',
    as_name=autoscaling_group, scaling_adjustment=-1, cooldown=180)

# The policy objects are now defined locally.
# Let's submit them to AWS.
autoscale.create_scaling_policy(scale_up_policy)
autoscale.create_scaling_policy(scale_down_policy)

# Now that the polices have been digested by AWS, they have extra properties
# that we aren't aware of locally. We need to refresh them by requesting them
# back again. 
# Specifically we'll need the Amazon Resource Name (ARN) of each policy.
scale_up_policy = autoscale.get_all_policies(
    as_group=autoscaling_group, policy_names=['scale_up'])[0]

scale_down_policy = autoscale.get_all_policies(
    as_group=autoscaling_group, policy_names=['scale_down'])[0]

# Now we'll create CloudWatch alarms that will define _when_ to run the
# Auto Scaling policies.

# We wan't to measure the average CPU usage across the whole Auto Scaling
# group, rather than individual instances. We can define that as a CloudWatch
# "Dimension".
alarm_dimensions = {"AutoScalingGroupName": autoscaling_group}

# One alarm for when to scale up...
scale_up_alarm = MetricAlarm(
        name='scale_up_on_cpu', namespace='AWS/EC2',
        metric='CPUUtilization', statistic='Average',
        comparison='>', threshold='70',
        period='60', evaluation_periods=2,
        alarm_actions=[scale_up_policy.policy_arn],
        dimensions=alarm_dimensions)
cloudwatch.create_alarm(scale_up_alarm)

# ...and one for when to scale down.
scale_down_alarm = MetricAlarm(
        name='scale_down_on_cpu', namespace='AWS/EC2',
        metric='CPUUtilization', statistic='Average',
        comparison='<', threshold='40',
        period='60', evaluation_periods=2,
        alarm_actions=[scale_down_policy.policy_arn],
        dimensions=alarm_dimensions)
cloudwatch.create_alarm(scale_down_alarm)