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Using Alarms and Alarm Actions in CloudWatch

These Go examples show you how to change the state of your Amazon EC2 instances automatically based on a CloudWatch alarm, as follows:

You can download complete versions of these example files from the aws-doc-sdk-examples repository on GitHub.

Scenario

You can use alarm actions to 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 instance to be running. You can use the reboot and recover actions to automatically reboot the instance.

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

Prerequisites

Create and Enable Actions on an Alarm

Choose Copy to save the code locally.

Create the file create_enable_alarms.go.

Import packages used in the example.

import (
    "github.com/aws/aws-sdk-go/aws"
    "github.com/aws/aws-sdk-go/aws/session"
    "github.com/aws/aws-sdk-go/service/cloudwatch"

    "fmt"
    "os"
)

Get an instance name, value, and alarm name.

if len(os.Args) != 4 {
    fmt.Println("You must supply an instance name, value, and alarm name")
    os.Exit(1)
}

instance := os.Args[1]
value := os.Args[2]
name := os.Args[3]

Initialize a session that the SDK will use to load credentials from the shared credentials file ~/.aws/credentials, load your configuration from the shared configuration file ~/.aws/config, and create a CloudWatch client.

sess := session.Must(session.NewSessionWithOptions(session.Options{
    SharedConfigState: session.SharedConfigEnable,
}))

// Create new CloudWatch client.
svc := cloudwatch.New(sess)

Create a metric alarm that reboots an instance if its CPU utilization is greater than 70 percent.

_, err := svc.PutMetricAlarm(&cloudwatch.PutMetricAlarmInput{
    AlarmName:          aws.String(name),
    ComparisonOperator: aws.String(cloudwatch.ComparisonOperatorGreaterThanThreshold),
    EvaluationPeriods:  aws.Int64(1),
    MetricName:         aws.String("CPUUtilization"),
    Namespace:          aws.String("AWS/EC2"),
    Period:             aws.Int64(60),
    Statistic:          aws.String(cloudwatch.StatisticAverage),
    Threshold:          aws.Float64(70.0),
    ActionsEnabled:     aws.Bool(true),
    AlarmDescription:   aws.String("Alarm when server CPU exceeds 70%"),
    Unit:               aws.String(cloudwatch.StandardUnitSeconds),

    // This is apart of the default workflow actions. This one will reboot the instance, if the
    // alarm is triggered.
    AlarmActions: []*string{
        aws.String(fmt.Sprintf("arn:aws:swf:us-east-1:%s:action/actions/AWS_EC2.InstanceId.Reboot/1.0", instance)),
    },
    Dimensions: []*cloudwatch.Dimension{
        {
            Name:  aws.String("InstanceId"),
            Value: aws.String(value),
        },
    },
})

Call EnableAlarmActions with the new alarm for the instance, and display a message.

result, err := svc.EnableAlarmActions(&cloudwatch.EnableAlarmActionsInput{
    AlarmNames: []*string{
        aws.String(name),
    },
})
fmt.Println("Alarm action enabled", result)

See the complete example on GitHub.

Disable Actions on an Alarm

Choose Copy to save the code locally.

Create the file disable_alarm.go.

Import the packages used in the example.

import (
    "github.com/aws/aws-sdk-go/aws"
    "github.com/aws/aws-sdk-go/aws/session"
    "github.com/aws/aws-sdk-go/service/cloudwatch"

    "fmt"
    "os"
)

Get the name of the alarm from the command line.

if len(os.Args) != 2 {
    fmt.Println("You must supply an alarm name")
    os.Exit(1)
}

Initialize a session that the SDK will use to load credentials from the shared credentials file ~/.aws/credentials, load your configuration from the shared configuration file ~/.aws/config, and create a CloudWatch client.

sess := session.Must(session.NewSessionWithOptions(session.Options{
    SharedConfigState: session.SharedConfigEnable,
}))

// Create new CloudWatch client.
svc := cloudwatch.New(sess)

Call DisableAlarmActions to disable the actions for this alarm and display a message.

// Disable the alarm.
_, err := svc.DisableAlarmActions(&cloudwatch.DisableAlarmActionsInput{
    AlarmNames: []*string{
        aws.String(name),
    },
})
fmt.Println("Success")

See the complete example on GitHub.