Using Alarm Actions in Amazon CloudWatch

This Python example shows you how to:

• Create a CloudWatch alarm and enable actions
• Disable a CloudWatch alarm action

The Scenario

Using alarm actions, you can create alarms that automatically stop, terminate, reboot, or recover your Amazon EC2 instances. You can use the stop or terminate actions when you no longer need an EC2 instance to be running. You can use the reboot and recover actions to automatically reboot those instances.

In this example, Python code is used to define an alarm action in CloudWatch that triggers the reboot of an Amazon EC2 instance. The code uses the uses AWS SDK for Python to manage Amazon EC2 instances using these methods of the CloudWatch client class:

• put_metric_alarm.
• disable_alarm_actions.

For more information about CloudWatch alarm actions, see Create Alarms to Stop, Terminate, Reboot, or Recover an Instance in the Amazon CloudWatch User Guide.

All the example code for the Amazon Web Services (AWS) SDK for Python is available here on GitHub.

Prerequisite Task

• Configure your AWS credentials, as described in Quickstart.

• Create an IAM role whose policy grants permission to describe, reboot, stop, or terminate an Amazon EC2 instance. For more information about creating an IAM role, see Creating a Role to Delegate Permissions to an AWS Service in the IAM User Guide.

  Use the following role policy when creating the IAM role.

{
   "Version": "2012-10-17",
   "Statement": [
      {
         "Effect": "Allow",
         "Action": [
            "cloudwatch:Describe*",
            "ec2:Describe*",
            "ec2:RebootInstances",
            "ec2:StopInstances*",
            "ec2:TerminateInstances"
         ],
         "Resource": [
            "*"
         ]
      }
   ]
}

Create and Enable Actions on an Alarm

Create or update an alarm and associate it with the specified metric. Optionally, this operation can associate one or more Amazon SNS resources with the alarm.

When this operation creates an alarm, the alarm state is immediately set to INSUFFICIENT_DATA. The alarm is evaluated and its state is set appropriately. Any actions associated with the state are then executed.

When you update an existing alarm, its state is left unchanged, but the update completely overwrites the previous configuration of the alarm.

The example below shows how to:

• Create an alarm and enable actions using put_metric_alarm.

Example

import boto3

# Create CloudWatch client
cloudwatch = boto3.client('cloudwatch')

# Create alarm with actions enabled
cloudwatch.put_metric_alarm(
    AlarmName='Web_Server_CPU_Utilization',
    ComparisonOperator='GreaterThanThreshold',
    EvaluationPeriods=1,
    MetricName='CPUUtilization',
    Namespace='AWS/EC2',
    Period=60,
    Statistic='Average',
    Threshold=70.0,
    ActionsEnabled=True,
    AlarmActions=[
      'arn:aws:swf:us-west-2:{CUSTOMER_ACCOUNT}:action/actions/AWS_EC2.InstanceId.Reboot/1.0'
    ],
    AlarmDescription='Alarm when server CPU exceeds 70%',
    Dimensions=[
        {
          'Name': 'InstanceId',
          'Value': 'INSTANCE_ID'
        },
    ],
    Unit='Seconds'
)

Disable Actions on an Alarm

Disable the actions for the specified alarms. When an alarm's actions are disabled, the alarm actions do not execute when the alarm state changes.

The example below shows how to:

• Disable metric alarm actions using disable_alarm_actions.

Example

import boto3

# Create CloudWatch client
cloudwatch = boto3.client('cloudwatch')

# Disable alarm
cloudwatch.disable_alarm_actions(
  AlarmNames=['Web_Server_CPU_Utilization'],
)