# Create a CPU usage alarm
<a name="US_AlarmAtThresholdEC2"></a>

You can create an CloudWatch alarm that sends a notification using Amazon SNS when the alarm changes state from `OK` to `ALARM`.

The alarm changes to the `ALARM` state when the average CPU use of an EC2 instance exceeds a specified threshold for consecutive specified periods.

## Setting up a CPU usage alarm using the Amazon Web Services Management Console
<a name="cpu-usage-alarm-console"></a>

Use these steps to use the Amazon Web Services Management Console to create a CPU usage alarm.

**To create an alarm based on CPU usage**

1. Open the CloudWatch console at [https://console.amazonaws.cn/cloudwatch/](https://console.amazonaws.cn/cloudwatch/).

1. In the navigation pane, choose **Alarms**, **All Alarms**.

1. Choose **Create alarm**.

1. Choose **Select metric**.

1. In the **All metrics** tab, choose **EC2 metrics**.

1. Choose a metric category (for example, **Per-Instance Metrics**).

1. Find the row with the instance that you want listed in the **InstanceId** column and **CPUUtilization** in the **Metric Name** column. Select the check box next to this row, and choose **Select metric**.

1. Under **Specify metric and conditions**, for **Statistic** choose **Average**, choose one of the predefined percentiles, or specify a custom percentile (for example, **p95.45**).

1. Choose a period (for example, **5 minutes**).

1. Under **Conditions**, specify the following:

   1. For **Threshold type**, choose **Static**.

   1. For **Whenever CPUUtilization is**, specify **Greater**. Under **than...**, specify the threshold that is to trigger the alarm to go to ALARM state if the CPU utilization exceeds this percentage. For example, 70.

   1. Choose **Additional configuration**. For **Datapoints to alarm**, specify how many evaluation periods (data points) must be in the `ALARM` state to trigger the alarm. If the two values here match, you create an alarm that goes to `ALARM` state if that many consecutive periods are breaching.

      To create an M out of N alarm, specify a lower number for the first value than you specify for the second value. For more information, see [Alarm evaluation](alarm-evaluation.md).

   1. For **Missing data treatment**, choose how to have the alarm behave when some data points are missing. For more information, see [Configuring how CloudWatch alarms treat missing data](alarms-and-missing-data.md).

   1. If the alarm uses a percentile as the monitored statistic, a **Percentiles with low samples** box appears. Use it to choose whether to evaluate or ignore cases with low sample rates. If you choose **ignore (maintain alarm state)**, the current alarm state is always maintained when the sample size is too low. For more information, see [Percentile-based alarms and low data samples](percentiles-with-low-samples.md). 

1. Choose **Next**.

1. Under **Notification**, choose **In alarm** and select an SNS topic to notify when the alarm is in `ALARM` state

   To have the alarm send multiple notifications for the same alarm state or for different alarm states, choose **Add notification**.

   To have the alarm not send notifications, choose **Remove**.

1. When finished, choose **Next**.

1. Enter a name and description for the alarm. Then choose **Next**.

   The name must contain only UTF-8 characters, and can't contain ASCII control characters. The description can include markdown formatting, which is displayed only in the alarm **Details** tab in the CloudWatch console. The markdown can be useful to add links to runbooks or other internal resources.

1. Under **Preview and create**, confirm that the information and conditions are what you want, then choose **Create alarm**.

## Setting up a CPU usage alarm using the Amazon CLI
<a name="cpu-usage-alarm-cli"></a>

Use these steps to use the Amazon CLI to create a CPU usage alarm.

**To create an alarm based on CPU usage**

1. Set up an SNS topic. For more information, see [Setting up Amazon SNS notifications](Notify_Users_Alarm_Changes.md#US_SetupSNS).

1. Create an alarm using the [put-metric-alarm](https://docs.amazonaws.cn/cli/latest/reference/cloudwatch/put-metric-alarm.html) command as follows. 

   ```
   aws cloudwatch put-metric-alarm --alarm-name {{cpu-mon}} --alarm-description "Alarm when CPU exceeds 70%" --metric-name CPUUtilization --namespace AWS/EC2 --statistic Average --period {{300}} --threshold {{70}} --comparison-operator GreaterThanThreshold --dimensions  Name=InstanceId,Value={{i-12345678}} --evaluation-periods {{2}} --alarm-actions arn:aws:sns:{{us-east-1}}:{{111122223333}}:{{my-topic}} --unit Percent
   ```

1. Test the alarm by forcing an alarm state change using the [set-alarm-state](https://docs.amazonaws.cn/cli/latest/reference/cloudwatch/set-alarm-state.html) command.

   1. Change the alarm state from `INSUFFICIENT_DATA` to `OK`.

      ```
      aws cloudwatch set-alarm-state --alarm-name {{cpu-mon}} --state-reason "initializing" --state-value OK
      ```

   1. Change the alarm state from `OK` to `ALARM`.

      ```
      aws cloudwatch set-alarm-state --alarm-name {{cpu-mon}} --state-reason "initializing" --state-value ALARM
      ```

   1. Check that you have received a notification about the alarm.