WEBCHECK

An AWS Node.js Lambda Function to check if a website is up and running and raise an alarm if not

LambdaWebCheck.js is a simple Node.js function that makes an http get request and logs the response to a custom AWS CloudWatch metric. The metric can then be used to setup and raise an alarm if the url is not responding. The function is automatically triggered at a predefined interval or schedule by AWS CloudWatch Events infrastructure.

The setup procedure involves:

• configuring the code and preparing a zip package for upload to AWS Lambda;
• creating an AWS IAM execution role with permissions on CloudWatch;
• creating, configuring and testing the AWS Lambda function;
• creating a CloudWatch alarm based on the function metrics.

In detail:

1. Modify the code of LambdaWebCheck.js function setting the appropriate url
2. Run npm install --only=production to install the request package and create a LambdaWebCheck.zip file containing LambdaWebCheck.js and the node_modules folder
3. Login to your AWS account, goto IAM Console (Identity and Access Management), select Roles and
   • click button Create New Role; input cloudwatch-putmetric (or the role name you prefer) in the Role Name field and click button Next Step
   • within the AWS Service Roles select AWS Lambda and go the Attach Policy page
   • select CloudWatchFullAccess policy and click button Next Step
   • review your selection and click button Create Role
4. Goto Lambda Console and click on the Create a Lambda function button, then
   • select Node.js 4.3 in the Select runtime drop-down
   • select node-exec blueprint (this is not important, you can choose any) by clicking on its name
   • in the Configure triggers page click on the empty square and select CloudWatch Events - Schedule from the list
   • enter Rule name (eg.: exec-5-mins), Rule description (eg.: executes once every 5 minutes), select the appropriate option from the Schedule expression drop-down (eg.: rate(5 minutes))
   • don't select Enable trigger and click Next
   • in the Configure function page enter a Name (eg.: web-check-mysite), a Description, make sure Runtime is Node.js 4.3, change Code entry type to Upload a .ZIP file and select the LambdaWebCheck.zip created earlier
   • change Handler to LambdaWebCheck.handler
   • select Choose an existing role from the Role drop-down and select cloudwatch-putmetric (or the role you defined in step 3) from the Existing role drop-down
   • in the Advanced settings set Timeout at 30 seconds and click Next
   • review your settings and click Create function
   • click on Test, ignore the content of the input test event (we are not using it) and click Save and test
   • if all is well you will see a success log, otherwise you need to troubleshoot the configuration error and test again until it is fixed
   • now select the Triggers tab and enable the CloudWatch event schedule we defined above
5. Goto CloudWatch Console, select Alarms and click on the Create Alarm button
   • select ActValue from Custom Metrics drop-down
   • select the url you configured and click Next
   • enter alarm name and description (eg: mywebsite not responding)
   • set the following Whenever expression: >= 1 for 2 consecutive periods (assuming the Lambda function runs every 5 minutes, this means that the alarm is raised after 2 failed executions)
   • in the Action section, select a notification list o create a new one
   • click the button Create Alarm and hope you will never receive the alarm notification email ...