Tutorial / Cram Notes
CloudWatch Metrics:
Metrics are the fundamental concept in CloudWatch and represent a time-ordered set of data points. They are defined by a name, a namespace, and zero or more dimensions.
- Standard Metrics: These are the metrics that AWS services provide by default. For example, EC2 instances automatically send metrics to CloudWatch for CPU utilization, disk I/O, and network usage.
- Custom Metrics: These metrics are published directly to CloudWatch by the user. You can use custom metrics to monitor application-specific data or monitor a resource that does not emit its own metrics.
CloudWatch Alarms:
Alarms watch a single metric or math expression over a time period you specify, and perform one or more actions when the value of the metric crosses a threshold over a number of time periods.
Associating CloudWatch Alarms with Standard Metrics
To create an alarm that monitors a standard metric provided by an AWS service, follow these steps:
- Open the CloudWatch console at https://console.aws.amazon.com/cloudwatch/.
- Navigate to the Alarms section and click on ‘Create Alarm’.
- Select the metric you want to create an alarm for. For instance, you can select EC2 metrics by browsing to ‘EC2 > Per-Instance Metrics’.
- Choose the metric you want to monitor, then click on ‘Select Metric’.
- Set the conditions for your alarm. You must choose when an alarm is triggered based on the metric’s value exceeding a certain threshold.
- Configure actions that the alarm should take when triggered, such as notifying an SNS topic.
- Assign a name for the alarm and add an optional description.
- Review and create the alarm.
For example, to monitor CPU utilization above 80% on an EC2 instance:
Threshold: Greater than 80%
Period: 5 minutes (a period during which the CPU utilization is measured)
Evaluation Periods: 2 (the number of consecutive periods the metric must be above the threshold before the alarm state is triggered)
Associating CloudWatch Alarms with Custom Metrics
Creating an alarm based on a custom metric follows a similar process, but first, you must publish the custom metric to CloudWatch.
To publish a custom metric:
aws cloudwatch put-metric-data –metric-name BufferMissPercentage –namespace MyNamespace –value 70 –unit Percent
Then, you would create an alarm for that custom metric:
- Navigate to the ‘Create Alarm’ wizard in CloudWatch.
- Select the custom metric within the ‘MyNamespace’ namespace.
- Specify the threshold, period, and evaluation periods for the alarm.
- Configure actions as needed.
For example, if you want to monitor ‘BufferMissPercentage’ exceeding 70%:
Threshold: Greater than 70%
Period: 1 minute
Evaluation Periods: 3
Important Considerations
| Aspect | Standard Metrics | Custom Metrics |
|---|---|---|
| Available Metrics | Pre-defined by AWS services. | Must be published to CloudWatch by the user. |
| Resolution | 1-minute and 5-minute granularity. | 1-minute granularity for higher-resolution metrics; standard is 5 minutes. |
| Charges | Free for default metrics; charges apply for additional data requests and higher resolution. | Charges apply for the storage of custom metrics and each PutMetricData API request. |
Conclusion
Monitoring AWS resources effectively with CloudWatch involves the appropriate use of both standard metrics that AWS services provide and custom metrics that you can define for specific use cases. Creating alarms based on these metrics allows DevOps engineers to take automated actions and receive notifications when key infrastructure components are not performing as expected. Understanding these concepts and their application is crucial for the AWS Certified DevOps Engineer – Professional exam, ensuring that you can maintain a robust, scalable, and reliable AWS environment.
Practice Test with Explanation
True or False: You can associate multiple alarms with a single CloudWatch metric.
True
In AWS CloudWatch, you can create multiple alarms for a single metric, each with different conditions or thresholds.
True or False: CloudWatch alarms can be created for custom metrics but not for standard metrics.
False
CloudWatch alarms can be created for both standard metrics provided by AWS services and custom metrics sent to CloudWatch by the user.
Which AWS service can you use to create custom metrics that will trigger CloudWatch alarms?
- A) AWS Lambda
- B) AWS CloudTrail
- C) Amazon S3
- D) Amazon EC2
A) AWS Lambda
AWS Lambda can be used to run code in response to triggers such as changes in data, and it can also publish custom metrics to CloudWatch, which can then trigger alarms.
True or False: CloudWatch alarms can trigger auto-scaling actions based on the metric they are monitoring.
True
CloudWatch alarms can initiate auto-scaling actions when certain thresholds are breached for a given metric, which is a common use case to automatically adjust the number of EC2 instances in response to load.
What kind of action can a CloudWatch alarm take upon state change?
- A) Launch EC2 instances
- B) Send an SNS notification
- C) Terminate RDS instances
- D) All of the above
B) Send an SNS notification
CloudWatch alarms can perform several actions on state change; however, actions like launching or terminating EC2/RDS instances are typically managed by Auto Scaling, not directly by CloudWatch alarms. CloudWatch alarms can send notifications through SNS.
True or False: It’s not possible to adjust the period over which a CloudWatch metric is evaluated for an alarm.
False
You can customize the evaluation period for CloudWatch alarms to span from one minute to several hours, depending on how frequently your metric data points are available.
Which of the following is NOT a valid state for a CloudWatch alarm?
- A) OK
- B) ALARM
- C) INSUFFICIENT_DATA
- D) DISABLED
D) DISABLED
CloudWatch alarms have three states: OK, ALARM, and INSUFFICIENT_DATA. There is no “DISABLED” state; however, you can disable actions on an alarm.
True or False: You can create CloudWatch alarms using the AWS Management Console, AWS CLI, and AWS SDKs.
True
You can create, configure, and manage CloudWatch alarms through various methods including the AWS Management Console, AWS Command Line Interface (CLI), and AWS Software Development Kits (SDKs).
What does it mean when a CloudWatch alarm is in the ‘ALARM’ state?
- A) The metric is within the defined threshold.
- B) The metric is beyond the defined threshold.
- C) The alarm has been disabled.
- D) CloudWatch has no data for the metric.
B) The metric is beyond the defined threshold.
The ‘ALARM’ state indicates that the metric has breached the threshold specified in the alarm’s conditions.
Which feature allows you to view logs, metrics, and traces in a unified interface in CloudWatch?
- A) CloudWatch Logs Insights
- B) CloudWatch Dashboards
- C) CloudWatch Synthetics
- D) CloudWatch ServiceLens
D) CloudWatch ServiceLens
CloudWatch ServiceLens integrates logs, metrics, and traces, providing a unified view to better understand and diagnose the health and performance of applications and their underlying AWS resources.
True or False: Alarms in CloudWatch can only be set for predefined threshold types.
False
CloudWatch allows setting alarms on thresholds defined by the user, which can be static thresholds or based on anomaly detection models.
When creating a CloudWatch alarm, which statistic indicates the most recent data point for the specified metric?
- A) Average
- B) Sum
- C) Minimum
- D) SampleCount
- E) Maximum
E) Maximum
The statistics determine how the metric data points are aggregated. The “Maximum” statistic reflects the most recent data point if the metric is continuously incremented or has a steady maximum value, such as a count that resets at intervals. However, keep in mind that the “most recent” data point may not always be represented by the maximum value depending on the nature of the metric being monitored.
Interview Questions
Can you explain how to create a CloudWatch alarm based on a standard EC2 metric such as CPU utilization?
To create a CloudWatch alarm based on a standard EC2 metric like CPU utilization, you navigate to the CloudWatch console, select Alarms, and click Create Alarm. Then, you choose the EC2 metric (e.g., CPUUtilization), specify the threshold value, and set the conditions that will trigger the alarm. You can then assign actions such as sending a notification or taking automated recovery actions.
How would you configure an alarm to react to a custom metric that you’ve published to CloudWatch?
After publishing a custom metric to CloudWatch, you would follow a similar process to that of standard metrics. Go to the CloudWatch console, choose Alarms, and start the Create Alarm wizard. Then you would select your custom metric under the Custom Metrics namespace, define the threshold and conditions, and configure the notification action or automated response you desire.
What are some differences between standard and custom CloudWatch metrics that you should be aware of when setting alarms?
Standard metrics are provided by AWS services like EC2, RDS, etc., and are automatically collected and sent to CloudWatch. On the other hand, custom metrics are user-defined, requiring the user to use the PutMetricData API or CLI to send the data to CloudWatch. Standard metrics have predefined statistics, whereas custom metrics can have unique statistics based on what is being sent. Alarms on custom metrics should be created with these custom data’s granularities and dimensions in mind.
What is the importance of the period and evaluation periods when configuring a CloudWatch alarm?
The period is the length of time associated with a specific CloudWatch metric data point, while the evaluation period is the number of the most recent periods, or data points, to evaluate to determine alarm state. These are crucial for alarm sensitivity and accuracy; shorter periods may trigger alarms more quickly but with more noise, while longer periods may reduce false alarms but take longer to raise a critical alarm.
Can you associate multiple CloudWatch alarms with a single metric? How would this be useful?
Yes, you can associate multiple alarms with a single CloudWatch metric, each with different thresholds and actions. This is useful for defining various levels of response – for example, one alarm could notify a DevOps engineer when CPU utilization exceeds 70%, while another could perform auto-scaling or shutdown actions at 90%.
How would you set up a CloudWatch alarm based on a combination of metrics?
You can use CloudWatch Metric Math to create expressions that aggregate and transform multiple metrics, then base your alarm on the result of these expressions. This allows you to capture more complex conditions for your alarm, such as averaging the CPU utilization of an entire Auto Scaling group.
What are Composite Alarms in CloudWatch, and how do they enhance alarm management?
Composite Alarms allow you to combine multiple alarms to form a single alarm with its own state. It helps in reducing alarm noise and focusing on critical issues by allowing you to specify a rule such that a composite alarm only triggers when multiple conditions are met, rather than reacting to a single metric threshold breach.
Describe a scenario where it would be appropriate to use percentile-based CloudWatch alarms.
Percentile-based alarms are appropriate when you need to account for outliers or variability in your metrics. For example, you might create an alarm based on the p90 (90th percentile) of your application’s response time. This would trigger an alarm for the higher end of response times without being affected by unusually low or high values that might skew average-based alarms.
What is the purpose of configuring alarm actions, and what are some of the actions you can take when an alarm changes state?
Alarm actions are used to specify what automated actions to take when an alarm changes state. These can include sending notifications via SNS, stopping, terminating, rebooting, or recovering EC2 instances, or even triggering auto-scaling policies. The purpose is to create a responsive and automated system that reacts to changes in your infrastructure’s performance or health.
How could you temporarily disable a CloudWatch alarm without deleting it?
You can temporarily disable a CloudWatch alarm by changing its state to “Disabled” in the CloudWatch console or by using the DisableAlarmActions API call. This stops the alarm from executing its assigned actions without the need to delete it.
What is meant by “missing data treatment” in CloudWatch alarms, and what options do you have for handling it?
Missing data treatment in CloudWatch alarms refers to the action taken when a metric is expected but not received (possibly due to the metric source being unavailable). You can choose to treat the missing data as missing, notBreaching, breaching, or ignore, which determines how the alarm interprets and reacts to the absence of data.
How can you ensure your CloudWatch alarms are as cost-effective as possible?
To make CloudWatch alarms cost-effective, you should opt for default metrics where possible instead of high-resolution custom metrics, and only create alarms that are necessary for the monitoring and automation of your applications. Also, optimize the number of evaluation periods and data granularity to balance between response time and unnecessary alarm triggers.
Great information on associating CloudWatch alarms with CloudWatch metrics. This is exactly what I needed for my exam prep!
Can someone explain the difference between standard and custom CloudWatch metrics?
Thanks for the detailed post!
Is there a limit on the number of CloudWatch alarms that I can create?
Awesome blog post, it clarified a lot for me.
I think it would be helpful to include an example of how to create a custom metric and associate it with an alarm.
This blog post is very useful for those preparing for the AWS Certified DevOps Engineer exam.
How can you test if a CloudWatch alarm is working correctly?