Let’s take a look at another troubleshooting example, this time using distributing tracing. The Distributed tracing page displays all the traces for a particular function. Click on Distributed tracing:
Click on one of the Root Entry Spans that doesn’t contain errors (an example is highlighted in blue above) to drill down into a single invocation of your Lambda function, and then click on the Expand all link:
We can see here that RequestUnicorn is a simple Lambda function consisting of 3 spans. Spans represent the time spent in a service or a service function. The span count includes both in-process and cross-process spans, but in-process spans are collpased by default.
Clicking on an individual span, DynamoDB putItem in this case, provides performance data for that particular span. Distributed tracing is extremely valuable in diagnosing exactly where in your services and/or services function performance-related issues are taking place:
Click the X on the top right hand corner of the span details foldout to retirn to the Distributing tracing page. This time, click on a Root Entry Span that does contain an error (the error count is displayed in red in the final column of the table):
This time we see only two spans reported which means the error here was fatal and prevented the Lambda function from completing its execution. If we click on the RequestUnicorn span, we can dig a bit deeper:
Here we see the high level Performance data for the selected span - Average duration and throughput - as well as any errors, if they occurred. Click on Error Details to drill down a bit further:
Now we know that this particular Lambda invocation failed due to a ReferenceError where the variable username was referenced but not defined.
Finally, click on the Attributes tab. The Attributes tab provides useful information such as how the Lambda function was invoked (apiGateway), what URL the user attempted to access (/ride), and what application deployment stage the function is located in (prod):
Scroll through the entire Attributes tab to see all the information it provides.