I want to monitor the CPU utilization of my Amazon Elastic Compute Cloud (EC2) instance. How can I do this using Amazon CloudWatch?

You can create a custom CloudWatch metric for your EC2 instance statistics by creating a script through the AWS Command Line Interface (AWS CLI). Then, you can monitor that metric by pushing it to CloudWatch.

Before proceeding, be sure that you install and configure the AWS CLI for use with the instance that you want to monitor.

Create a custom CloudWatch metric

To create your custom metric:

1.    Log in to the instance through the AWS CLI.

2.    Copy the following Bash script, and then save it to your instance (for example, mem.sh).

This example script shows the values that you can publish in CloudWatch. In this example, we are using the put-metric-data API call to push the following values to CloudWatch: the percentage of used memory, the number of total and port 80 TCP connections, the number of users currently logged in, and the percentage of I/O wait time.

========Sample script======
USEDMEMORY=$(free -m | awk 'NR==2{printf "%.2f\t", $3*100/$2 }')
TCP_CONN=$(netstat -an | wc -l)
TCP_CONN_PORT_80=$(netstat -an | grep 80 | wc -l)
USERS=$(uptime |awk '{ print $6 }')
IO_WAIT=$(iostat | awk 'NR==4 {print $5}')
aws cloudwatch put-metric-data --metric-name memory-usage --dimensions Instance=i-0c51f9f1213e63159  --namespace "Custom" --value $USEDMEMORY
aws cloudwatch put-metric-data --metric-name Tcp_connections --dimensions Instance=i-0c51f9f1213e63159  --namespace "Custom" --value $TCP_CONN
aws cloudwatch put-metric-data --metric-name TCP_connection_on_port_80 --dimensions Instance=i-0c51f9f1213e63159  --namespace "Custom" --value $TCP_CONN_PORT_80
aws cloudwatch put-metric-data --metric-name No_of_users --dimensions Instance=i-0c51f9f1213e63159  --namespace "Custom" --value $USERS
aws cloudwatch put-metric-data --metric-name IO_WAIT --dimensions Instance=i-0c51f9f1213e63159  --namespace "Custom" --value $IO_WAIT

3.    After creating the Bash script, give execute permissions to the file.

$ chmod +x mem.sh

4.    Run the Bash script to check that it works.

Push your metric to CloudWatch

1.    Create a cron job:

$ crontab -e

2.    Add this line to execute your script every minute:

*/1 * * * * /home/ec2-user/mem.sh

3.    Save and exit.

When the crontab is saved, crontab: installing new crontab is displayed.

Monitor your EC2 instance

Find your custom metric in the CloudWatch console:

1.    Sign in to the CloudWatch console.

2.    Choose Metrics.

3.    Choose the All Metrics view.

4.    Choose Custom.

5.    Choose the dimension Instance.

6.    Select your custom metric by its InstanceId and Metric Name.

7.    View the graph of your metric.

Other uses

You can use this example to build your own logic to process multiple dimensions (memory, CPU, swap, and so on), and then push that metric data to CloudWatch.

For example, suppose that you benchmark your application. Then, you discover that when the I/O wait time and percentage memory usage reach a certain threshold, the system stops functioning properly. To address this problem, you monitor both values simultaneously in a script, storing the logical AND of the values in a third variable that you push to CloudWatch.

if [[  $IO_WAIT > 70 && $USEDMEMORY > 80 ]]
aws cloudwatch put-metric-data --metric-name danger --dimensions Instance=i-0c51f9f1213e63159  --namespace "Custom" --value $c

For normal conditions, this variable is 0 (zero). For situations when both conditions are met, the value is set to 1 (one). You can then build custom alarms around these parameters to warn of problematic situations for your system.

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Published: 2018-07-25