lab7

Monitor and Chart Coldstarts

In the intro, we learned that coldstarts impact the response time.

Wouldn't it be interesting to see them in Dynatrace?

While this is not (yet) available out-of-the-box, we can use the Dynatrace OneAgent SDK to annotate the data.

This SDK comes via npm and was already used to connect the PurePath in previous examples, so we don't have to install it now.

All we have to do, is to add a bit of code.

How can we detect coldstarts? We can use the fact, that Lambda functions in Node.js have a global scope as well. It's everything that's not in the handler function.

So if we store a flag there, its status can tell use if the whole function was newly deployed.

For your convenience, the code is already in place and just needs to be uncommented.

So in queueNote.js we add:

let isColdStart = true;

Now in the function we have to check this flag and send the data to the Dynatrace:

if (isColdStart) {
  console.log('This is a coldstart');
  dsdk.addCustomRequestAttribute('coldstart', 'yes');
  isColdStart = false;
} else {
  dsdk.addCustomRequestAttribute('coldstart', 'no');
}

That's it - let's also do that in addNote.js. Here we also have to uncomment the initialization of the SDK as we didn't need it in the previous example:

const DSDK = require('@dynatrace/oneagent-sdk');
const dsdk = DSDK.createInstance();

Additionally, let's also track the detected sentiment.

Now, all that's left to do is to deploy the function with npx serverless deploy.

To make the data available in Dynatrace, we have to add a bit of Configuration to it:

Step-by-step Guide

1. In Dynatrace go to Settings -> Serverside monitoring -> Request attributes

2. Click on Create new request attribute

3. Fill out the form as shown on the screenshot and don't forget to save at the end

4. Do the same for the request attribute coldstart and call it Lambda Coldstart

5. Now hit the API a few times and soon the data will show up as separate tab on service requests (analyzeNote: Service -> Show requests).

   

6. Click on Create chart to create a chart for this service and its attributes

7. Change the response time metric as shown on the screenhot

   

   By hovering over the chart we can see the response time impact due to coldstarts.

8. Click on Save to service to create a shortcut for your services screen.

9. We can also create a chart that shows response time versus sentiment

   

   And when we hover over the metrics, we see that positive sentiments take longer. The difference is the time needed to talk to DynamoDB.

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