Serverless Spy Vs Spy Chapter 1: X-ray

There are several ways to perform espionage activities in the life of a serverless app, which all battle for your attention. Time for the advent of counterintelligence: We want answers! - And CDK/Source examples of how to use it! Here we go, Serverless spy vs spy in four chapters, each post published after you light the next candle.


Serverless observability concepts


This concept map shows the observability domain. With practical examples, I will explore the concepts one by one. Starting with X-Ray.

The X-Ray Service and the X-Ray SDK

In serverless development, we have the problem of the “missing cloud profiler”. We cannot look into the distributed Lambda Function/services to see where performance bottlenecks are.

Let`s assume we have a Function which is calling another Service:


We test the function (1) and get results, how long it takes:

REPORT RequestId: c7e872b4-1fd4-492b-81f9-8cf22d67827b Duration: 83.23 ms Billed Duration: 84 ms Memory Size: 1024 MB Max Memory Used: 47 MB Init Duration: 172.27 ms

We know about warm/cold start and call again:

REPORT RequestId: 99b658c0-d946-4f17-bed1-890668051b74 Duration: 9.31 ms Billed Duration: 10 ms Memory Size: 1024 MB Max Memory Used: 47 MB

The part-whole problem

What we do not know is how much time was spent in segment A and how much is spent in segment B. We only know A+B.


So this is your espionage order!

The distribution problem

We could do some logging. But another problem comes into mind: The duration of each lambda call is statistically distributed. That means the value for a single call could be way off. So we have to look at a bunch of calls.

The every-single-service problem

Now assume we are working with several AWS service calls. With logging, we had to log before and after each call.

After solving all the problems, we have to create some software for analysis.

To solve this with logging alone, you need correlation IDs in each log and have to search all logs events.


The correlation ID is called TraceID. And tracing gets all information about a request aggregated by request. In doing this, you can trace the call of a single session through all services.

X-Ray is the tracing solution on AWS.

How X-Ray works

The part-whole solution

In X-Ray, we have segments and sub-segments. We see A, B and A+B segments.

The distribution solution

All services must send data about their communication to a central tracing service so we also have an overview of what is happening.

The every-single-service problem

With the AWS SDK, the X-Ray SDK hooks itself into all AWS service calls. So we do not have to decorate each call, it is done automatically for you.

Getting started

We use a modified simple lambda application from tecRacer serverless sample application. Get the modified source for this post from github: xraystarter and leave a star :)

sample app

The simple architecture of the base serverless application.

  1. The client uploads a file to an S3 bucket
  2. The Lambda function gets an event
  3. The Lambda service and the Lambda function write logs
  4. The Lambda function writes the key of the file to dynamodb

As the examples are for three Lambda functions: TypeScript, Python and GO, we change the architecture a bit:

sample app

I will walk you through deploying the application to see some X-Ray traces.


You have to have the tools installed. With these tools on a mac, the steps are automated.


This is the Infrastructure as Code tool.


This is the better makefile to allow you to deploy the example.


We need a Docker daemon, as the Python and the TypeScript Lambda functions need more tools installed to be built. This is simplified with Docker, and the use of the CDK Constructs NodejsFunction and PythonFunction. The GO Lambda just needs GO to be build.

If you want to change it to a standard CDK Lambda Function, you can do a task fastdeploy in the Lambda directories to update just the Lambda Function code:

├── go
│   ├── Taskfile.yml
│   ├── dist
│   ├── go.mod
│   ├── go.sum
│   └── main
├── py
│   ├── Taskfile.yml
│   ├──
│   ├──
│   ├── dist
│   ├── package
│   └── requirements.txt
└── ts
    ├── Taskfile.yml
    ├── dist
    ├── index.ts
    ├── node_modules
    ├── package-lock.json
    ├── package.json
    ├── test
    └── tsconfig.json

Start Docker

Because of the Docker Desktop policies I replace Docker Desktop with Colima.


task colima

The Output is like:

task: [colima] colima start
INFO[0000] starting colima
INFO[0022] starting ...                                  context=docker
INFO[0027] done

Boostrap Account for cdk

If you use AWS CDK for the first time


task bootstrap

Output like:

task: [bootstrap] npx cdk@2.51.1  bootstrap
Sending build context to Docker daemon  54.27kB
Step 1/12 : ARG
 ⏳  Bootstrapping environment aws://123456789012/eu-central-1...
 ✅  Environment aws://123456789012/eu-central-1 bootstrapped.

Deploy application


task deploy

Output like:

Step 1/12 : ARG

 ✅  xraystarter

✨  Deployment time: 105.63s

xraystarter.BucketName = xraystarter-incoming0b397865-1hx8j3qf51d0x
xraystarter.LambdaNameGo = xraystarter-go
xraystarter.LambdaNamePy = xraystarter-py
xraystarter.LambdaNameTS = xraystarter-ts
xraystarter.TableName = items
Stack ARN:

✨  Total time: 110.91s

Now we are ready to use the application.

Generate Traffic



This puts files on the S3 bucket, and the Lambda Functions are triggered. Stop after 2 cycles.

A Look at X-Ray

X-Ray Service Map

The first thing I look at is the Service Map. You get there in the AWS Console choosing Cloudwatch -> X-Ray traces -> Service Map:

sample app

The map for all three lambdas first looked like this:

Map 1

Spy on an error: A Python Problem


We see at first glance that the python Function xraystarter-py has a Problem! Now we can use the traces and the logs to find the cause of the problem.

Map 1

You see that the invocation itself got an error. A click leads us to “View in CloudWatch Logs insights”

Insights 1

With problems inside the application, you get all log events here. But because this is an problem before the function is executed, the error is published by the Lambda service and does not have an ID in the log event. Therefore we find the whole log stream itself.

With the requestId b510437d-... you find the log stream in Lambda recent invocations:

Recent invocations 1

In the log itself you find:

[ERROR] Runtime.ImportModuleError: Unable to import module 'app': No module named 'aws_xray_sdk'
Traceback (most recent call last):

Looks like the CDK construct from aws-lambda-python-alpha did not include the X-Ray library. Well, its alpha, so OK:

import { PythonFunction } from '@aws-cdk/aws-lambda-python-alpha';


In the directory of the Python Lambda function we have a task fastdeploy, which updates just the function code, but with all libraries:

cd lambda/py
task fastdeploy

What it does:

  1. Create a complete zip with the X-Ray sdk
      - pip install --target ./package -r requirements.txt
      - cd package && zip -r ../ .
      - zip
      - mv dist/
  1. Update the function code
        sh: aws cloudformation list-exports --query "Exports[?Name == 'xraystarter-py-name'].Value" --output text
      - aws lambda update-function-code --function-name  {{.FN}} --zip-file fileb://dist/

The name of the Lambda Function is exported, so we get it with cloudformation list-exports.

See the lambda/py/Taskfile.yml for the code.

Run again

We wait 15 mins, so that the old data is not shown (if we filter on that time range). Then again create traffic:




So 27 Nov 2022 18:53:58 CET
upload: ./ to s3://xraystarter-incoming0b397865-1hx8j3qf51d0x//test-20-0-0-0
So 27 Nov 2022 18:54:09 CET
upload: ./ to s3://xraystarter-incoming0b397865-1hx8j3qf51d0x//test-20-0-0-1

Cleared Service Map

Cleared Map

The (1) xraystarter-py has zero errors and writes to the items table (2). Node and Python SDK propagate the table name to X-Ray, and the GO X-Ray SDK behaves differently (3). But all Lambda Functions write to the same table.

How to instrument X-Ray on Lambda

The XRay SDKs contains all function to send tracing information from the Lambda Function to the X-Ray server. Witch activated X-Ray, the Lambda Service sends information too.

Step 1) Create Lambda Services with Y-Ray support

See lib/xraystarter-stack.ts for details.


const fnTS = new NodejsFunction(this, "xraystarter-ts", {
  tracing: aws_lambda.Tracing.ACTIVE,


const fnPy = new PythonFunction(this, 'xraystarter-py', {
  tracing: aws_lambda.Tracing.ACTIVE,


const fnGO = new aws_lambda.Function(this, 'xraystarter-go', {
  tracing: aws_lambda.Tracing.ACTIVE,

Step 2) Load the X-Ray SDK


import * as AWSXRay from 'aws-xray-sdk'


from aws_xray_sdk.core import xray_recorder
from aws_xray_sdk.core import patch_all


import (


Step 3) bind aws calls to xray


In Ts you create a constant which replaces the normal creation of a client:

import * as AWS from 'aws-sdk';
const dynamodb = new AWS.DynamoDB();

Patch AWS variable with:

const AWS = AWSXRay.captureAWS(require('aws-sdk'));

You see in the node xrays sdk that each AWS service is customized with the captureAWSRequest function, which is responsible for the X-Ray calls.

  for (var prop in awssdk) {
    if (awssdk[prop].serviceIdentifier) {
      var Service = awssdk[prop];


In python you just call a function to do the patching.


The nested magic is happening in the function of the SDK.

A def _patch_func(parent, func_name, func, modifier=lambda x: x): calls a setattr:

setattr(parent, func_name, modifier(xray_recorder.capture(name=capture_name)(func)))


In GO, you intercept the middleware.

In GO SDK V2, you can change the client request pipeline directly. This way, you can add behaviour before or after each step of an AWS api call.

	cfg, err := config.LoadDefaultConfig(context.TODO())
	if err != nil {
		panic("unable to load SDK config, " + err.Error())
	// Using the Config value, create the DynamoDB client
	Client = dynamodb.NewFromConfig(cfg)

When you look at the GO X-Ray SDK you can see in func initializeMiddlewareAfter(stack *middleware.Stack) how the calls to X-Ray are generated. The call to X-Ray happens in the deserialize step.

Back to espionage order: Query traces

Query Traces of a single service

In CloudWatch > Traces we now run a query for each service:


  1. Set filter
  2. Run query


Query: service(id(name: "xraystarter-ts", type: "AWS::Lambda"))

Timeline ts

Segments Timeline


Query: service(id(name: "xraystarter-py", type: "AWS::Lambda"))

Timeline py

Segments Timeline


Query: service(id(name: "xraystarter-go", type: "AWS::Lambda"))

Timeline go

Segments Timeline

Analyze traces

Dwell Time

A surprise is a time spent in the Lambda service, which is 39…92 ms. The next subsegment is a dwell time, which only appears if the lambda is called via SNS/S3.

You can optimize your Function code, but that would not affect the dwell time. Calling the Function directly from the console gives a trace with no dwell time:

Timeline go


Because the X-Ray trace is sent within the Lambda Function, you do not only measure the response time from DynamoDB but also the performance of the Function and the development language. But don`t take these times seriously because the execution time is also not constant.

An example for the GO Lambda:

TraceId  Call  Dynamodb Time
1-63847262-1f7b1f131c705dd37c779140  Cold start with event 1  81ms
1-63847264-35ce354a5be7eaa51c808a04  Warm start with same event 1  4ms
1-638472d9-0651242b5c645fd552266041  Warm start with new event 2  32ms
1-63847361-4f18e808597dc00552100afe  Warm start with same event 2  25 ms

And the same for Python Lambda

TraceId  Call  Dynamodb Time
1-638475c3-0a4d8fcb05b4bb3c71bf0e28  Cold start with event 1 53ms
1-638475c7-3ca3074d4977478344f0191e  Warm start with same event 1 41ms
1-638475d8-4a0ef8842a7bf9b5663412fc  Warm start with new event 2  39ms
1-638475d8-4fa68a674581da2f6ba79d1a  Warm start with same event 2  34ms


With X-Ray, you can have traceability and connect them to logs easily! As you dig deeper, you see additional overhead like the initialization or the dwell time. With the service map, you get a quick overview, and the references from traces to CloudWatch logs via Insights can help understand the whole microservice application.

This application is simple, so you can get X-Ray up and running and develop your own applications, which will be more complex. But the principle is the same.

If you need consulting for your serverless project, don’t hesitate to contact the sponsor of this blog, tecRacer.

For more AWS development stuff, follow me on dev

See also

Thanks to

  • Spy vs Spy - Comics which not everybody gets :)

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