Create an Alarm

Now that the right metric has been identified to monitor the dependency, it is time to create an alarm to monitor the metric and send notifications based on thresholds defined. CloudWatch Alarms can be used to automatically initiate actions on your behalf. An alarm watches a single metric over a specified time period, and performs one or more specified actions, based on the value of the metric relative to a threshold over time. The action is a notification sent to an Amazon SNS topic or an Auto Scaling policy.

An alarm needs to be created that checks the Lambda function invocation every minute to ensure that it has been invoked at least one time, and treats missing data as an indication that the function has not not been invoked, and as such the dependency that is being monitoring has failed. If the alarm is triggered, a notification should be sent to an SNS topic so that someone can be notified and respond, or an automatic remediation activity can be triggered as a result.

  1. Go to the Amazon CloudWatch console at https://console.aws.amazon.com/cloudwatch, click on Alarms, and then Create alarm

    CWAlarms

  2. Click on Select metric

  3. In the search bar under All metrics, enter the name of the data read function - WA-Lab-DataReadFunction and press enter

  4. In the metric breakdown, select Lambda > By Resource and you will see a list of Lambda metrics available

  5. Check the box for the metric Invocations and click Select metric

    CWAlarmSelectMetric

  6. On the Specify metric and conditions page, make the following changes for the Metric:

    • Change Statistic from Average to Sum
    • Change Period from 5 minutes to 1 minute

    CWAlarmSelectPeriod

  7. Scroll down to the Conditions section and configure it as follows:

    • Threshold type - set to Static
    • Whenever invocations is… - set to Lower
    • than… - enter 1 since this is the minimum number of invocations that is expected every minute
  8. Click on the arrow next to Additional Configuration to expand that section and make the following configuration changes:

    • Datapoints to alarm should be 1 out of 1
    • Missing data treatment should be set to Treat missing data as bad (breaching threshold) since Lambda will not report any metrics if a function was not invoked
  9. Click Next to go to the Configure actions page

    CWAlarmConditions

  10. Under Notification, make the following changes:

    • Alarm state trigger - select In alarm
    • Select an SNS topic - choose Select an existing SNS topic since a topic was created as part of the CloudFormation stack
    • Send a notification to… - select WA-Lab-Dependency-Notification and verify that the Email (endpoints) listed below is the same that was specified during stack creation
  11. Click Next to go to the Add name and description page

    CWAlarmAction

  12. Under Name and description, specify the following:

    • Alarm name - enter a recognizable name for the alarm such as WA-Lab-Dependency-Alarm
    • Alarm description - this is an optional field that can be left blank for this exercise

    CWAlarmName

  13. Click Next to go to the Preview and create page

  14. Click Create alarm

Once the alarm has been created, you will be returned to the Alarms page on the CloudWatch console. In the search bar, enter the name of the alarm that was just created WA-Lab-Dependency-Alarm. The alarm will be listed with a state of Insufficient data. This is because CloudWatch is currently evaluating the underlying metric to determine the current state. In a few minutes, you will see the alarm transition from Insufficient data to OK. Click on the alarm name to go to the alarm details page. Review contents of the page to understand the configuration of the alarm such as metric used, threshold set, evaluation interval, etc. The red line on the graph indicates the threshold that has been set for the alarm. Based on the alarm conditions, the alarm will go into an In alarm state if the metric graph falls below this threshold.

CWAlarmInsufficientData

Under the History section, you will be able to view all state changes with respect to the alarm. Once the alarm is in an OK state, you will see a State update event under History.

CWAlarmStateChange

An alarm has now been created on a suitable metric to identify if the external service that the workload is dependent on is experiencing outage. Additionally, notifications have been configured to alert relevant stakeholders when the workload outcome is at risk due to failure/unavailability of the external service.

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