All posts by Bharath Kumar

Instrumenting Web Apps Using AWS X-Ray

Post Syndicated from Bharath Kumar original

This post was written by James Bowman, Software Development Engineer, AWS X-Ray

AWS X-Ray helps developers analyze and debug distributed applications and underlying services in production. You can identify and analyze root-causes of performance issues and errors, understand customer impact, and extract statistical aggregations (such as histograms) for optimization.

In this blog post, I will provide a step-by-step walkthrough for enabling X-Ray tracing in the Go programming language. You can use these steps to add X-Ray tracing to any distributed application.

Revel: A web framework for the Go language

This section will assist you with designing a guestbook application. Skip to “Instrumenting with AWS X-Ray” section below if you already have a Go language application.

Revel is a web framework for the Go language. It facilitates the rapid development of web applications by providing a predefined framework for controllers, views, routes, filters, and more.

To get started with Revel, run revel new A project base is then copied to $GOPATH/src/

$ tree -L 2
├── app
│ ├── controllers
│ ├── init.go
│ ├── routes
│ ├── tmp
│ └── views
├── conf
│ ├── app.conf
│ └── routes
├── messages
│ └── sample.en
├── public
│ ├── css
│ ├── fonts
│ ├── img
│ └── js
└── tests
└── apptest.go

Writing a guestbook application

A basic guestbook application can consist of just two routes: one to sign the guestbook and another to list all entries.
Let’s set up these routes by adding a Book controller, which can be routed to by modifying ./conf/routes.

package controllers

import (


const TABLE_NAME = "guestbook"
const SUCCESS = "Success.\n"
const DAY = 86400


func init() {

// randString returns a random string of len n, used for DynamoDB Hash key.
func randString(n int) string {
    b := make([]rune, n)
    for i := range b {
        b[i] = letters[rand.Intn(len(letters))]
    return string(b)

// Book controls interactions with the guestbook.
type Book struct {
    ddbClient *dynamodb.DynamoDB

// Signature represents a user's signature.
type Signature struct {
    Message string
    Epoch   int64
    ID      string

// ddb returns the controller's DynamoDB client, instatiating a new client if necessary.
func (c Book) ddb() *dynamodb.DynamoDB {
    if c.ddbClient == nil {
        sess := session.Must(session.NewSession(&aws.Config{
            Region: aws.String(endpoints.UsWest2RegionID),
        c.ddbClient = dynamodb.New(sess)
    return c.ddbClient

// Sign allows users to sign the book.
// The message is to be passed as application/json typed content, listed under the "message" top level key.
func (c Book) Sign() revel.Result {
    var s Signature

    err := c.Params.BindJSON(&s)
    if err != nil {
        return c.RenderError(err)
    now := time.Now()
    s.Epoch = now.Unix()
    s.ID = randString(20)

    item, err := dynamodbattribute.MarshalMap(s)
    if err != nil {
        return c.RenderError(err)

    putItemInput := &dynamodb.PutItemInput{
        TableName: aws.String(TABLE_NAME),
        Item:      item,
    _, err = c.ddb().PutItem(putItemInput)
    if err != nil {
        return c.RenderError(err)

    return c.RenderText(SUCCESS)

// List allows users to list all signatures in the book.
func (c Book) List() revel.Result {
    scanInput := &dynamodb.ScanInput{
        TableName: aws.String(TABLE_NAME),
        Limit:     aws.Int64(100),
    res, err := c.ddb().Scan(scanInput)
    if err != nil {
        return c.RenderError(err)

    messages := make([]string, 0)
    for _, v := range res.Items {
        messages = append(messages, *(v["Message"].S))
    return c.RenderJSON(messages)

POST /sign Book.Sign
GET /list Book.List

Creating the resources and testing

For the purposes of this blog post, the application will be run and tested locally. We will store and retrieve messages from an Amazon DynamoDB table. Use the following AWS CLI command to create the guestbook table:

aws dynamodb create-table --region us-west-2 --table-name "guestbook" --attribute-definitions AttributeName=ID,AttributeType=S AttributeName=Epoch,AttributeType=N --key-schema AttributeName=ID,KeyType=HASH AttributeName=Epoch,KeyType=RANGE --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5

Now, let’s test our sign and list routes. If everything is working correctly, the following result appears:

$ curl -d '{"message":"Hello from cURL!"}' -H "Content-Type: application/json" http://localhost:9000/book/sign
$ curl http://localhost:9000/book/list
  "Hello from cURL!"

Integrating with AWS X-Ray

Download and run the AWS X-Ray daemon

The AWS SDKs emit trace segments over UDP on port 2000. (This port can be configured.) In order for the trace segments to make it to the X-Ray service, the daemon must listen on this port and batch the segments in calls to the PutTraceSegments API.
For information about downloading and running the X-Ray daemon, see the AWS X-Ray Developer Guide.

Installing the AWS X-Ray SDK for Go

To download the SDK from GitHub, run go get -u The SDK will appear in the $GOPATH.

Enabling the incoming request filter

The first step to instrumenting an application with AWS X-Ray is to enable the generation of trace segments on incoming requests. The SDK conveniently provides an implementation of http.Handler which does exactly that. To ensure incoming web requests travel through this handler, we can modify app/init.go, adding a custom function to be run on application start.

import (


func init() {

func installXRayHandler() {
    revel.Server.Handler = xray.Handler(xray.NewFixedSegmentNamer("GuestbookApp"), revel.Server.Handler)

The application will now emit a segment for each incoming web request. The service graph appears:

You can customize the name of the segment to make it more descriptive by providing an alternate implementation of SegmentNamer to xray.Handler. For example, you can use xray.NewDynamicSegmentNamer(fallback, pattern) in place of the fixed namer. This namer will use the host name from the incoming web request (if it matches pattern) as the segment name. This is often useful when you are trying to separate different instances of the same application.

In addition, HTTP-centric information such as method and URL is collected in the segment’s http subsection:

"http": {
    "request": {
        "url": "/book/list",
        "method": "GET",
        "user_agent": "curl/7.54.0",
        "client_ip": "::1"
    "response": {
        "status": 200

Instrumenting outbound calls

To provide detailed performance metrics for distributed applications, the AWS X-Ray SDK needs to measure the time it takes to make outbound requests. Trace context is passed to downstream services using the X-Amzn-Trace-Id header. To draw a detailed and accurate representation of a distributed application, outbound call instrumentation is required.

AWS SDK calls

The AWS X-Ray SDK for Go provides a one-line AWS client wrapper that enables the collection of detailed per-call metrics for any AWS client. We can modify the DynamoDB client instantiation to include this line:

// ddb returns the controller's DynamoDB client, instatiating a new client if necessary.
func (c Book) ddb() *dynamodb.DynamoDB {
    if c.ddbClient == nil {
        sess := session.Must(session.NewSession(&aws.Config{
            Region: aws.String(endpoints.UsWest2RegionID),
        c.ddbClient = dynamodb.New(sess)
        xray.AWS(c.ddbClient.Client) // add subsegment-generating X-Ray handlers to this client
    return c.ddbClient

We also need to ensure that the segment generated by our xray.Handler is passed to these AWS calls so that the X-Ray SDK knows to which segment these generated subsegments belong. In Go, the context.Context object is passed throughout the call path to achieve this goal. (In most other languages, some variant of ThreadLocal is used.) AWS clients provide a *WithContext method variant for each AWS operation, which we need to switch to:

_, err = c.ddb().PutItemWithContext(c.Request.Context(), putItemInput)
    res, err := c.ddb().ScanWithContext(c.Request.Context(), scanInput)

We now see much more detail in the Timeline view of the trace for the sign and list operations:

We can use this detail to help diagnose throttling on our DynamoDB table. In the following screenshot, the purple in the DynamoDB service graph node indicates that our table is underprovisioned. The red in the GuestbookApp node indicates that the application is throwing faults due to this throttling.

HTTP calls

Although the guestbook application does not make any non-AWS outbound HTTP calls in its current state, there is a similar one-liner to wrap HTTP clients that make outbound requests. xray.Client(c *http.Client) wraps an existing http.Client (or nil if you want to use a default HTTP client). For example:

resp, err := ctxhttp.Get(ctx, xray.Client(nil), "")

Instrumenting local operations

X-Ray can also assist in measuring the performance of local compute operations. To see this in action, let’s create a custom subsegment inside the randString method:

// randString returns a random string of len n, used for DynamoDB Hash key.
func randString(ctx context.Context, n int) string {
    xray.Capture(ctx, "randString", func(innerCtx context.Context) {
        b := make([]rune, n)
        for i := range b {
            b[i] = letters[rand.Intn(len(letters))]
        s := string(b)
    return s

// we'll also need to change the callsite

s.ID = randString(c.Request.Context(), 20)


By now, you are an expert on how to instrument X-Ray for your Go applications. Instrumenting X-Ray with your applications is an easy way to analyze and debug performance issues and understand customer impact. Please feel free to give any feedback or comments below.

For more information about advanced configuration of the AWS X-Ray SDK for Go, see the AWS X-Ray SDK for Go in the AWS X-Ray Developer Guide and the aws/aws-xray-sdk-go GitHub repository.

For more information about some of the advanced X-Ray features such as histograms, annotations, and filter expressions, see the Analyzing Performance for Amazon Rekognition Apps Written on AWS Lambda Using AWS X-Ray blog post.

Using Amazon CloudWatch and Amazon SNS to Notify when AWS X-Ray Detects Elevated Levels of Latency, Errors, and Faults in Your Application

Post Syndicated from Bharath Kumar original

AWS X-Ray helps developers analyze and debug production applications built using microservices or serverless architectures and quantify customer impact. With X-Ray, you can understand how your application and its underlying services are performing and identify and troubleshoot the root cause of performance issues and errors. You can use these insights to identify issues and opportunities for optimization.

In this blog post, I will show you how you can use Amazon CloudWatch and Amazon SNS to get notified when X-Ray detects high latency, errors, and faults in your application. Specifically, I will show you how to use this sample app to get notified through an email or SMS message when your end users observe high latencies or server-side errors when they use your application. You can customize the alarms and events by updating the sample app code.

Sample App Overview

The sample app uses the X-Ray GetServiceGraph API to get the following information:

  • Aggregated response time.
  • Requests that failed with 4xx status code (errors).
  • 429 status code (throttle).
  • 5xx status code (faults).
Sample app architecture

Overview of sample app architecture

Getting started

The sample app uses AWS CloudFormation to deploy the required resources.
To install the sample app:

  1. Run git clone to get the sample app.
  2. Update the JSON file in the Setup folder with threshold limits and notification details.
  3. Run the script to install the sample app.

For more information about the installation steps, see the readme file on GitHub.

You can update the app configuration to include your phone number or email to get notified when your application in X-Ray breaches the latency, error, and fault limits you set in the configuration. If you prefer to not provide your phone number and email, then you can use the CloudWatch alarm deployed by the sample app to monitor your application in X-Ray.

The sample app deploys resources with the sample app namespace you provided during setup. This enables you to have multiple sample apps in the same region.

CloudWatch rules

The sample app uses two CloudWatch rules:

  1. SCHEDULEDLAMBDAFOR-sample_app_name to trigger at regular intervals the AWS Lambda function that queries the GetServiceGraph API.
  2. XRAYALERTSFOR-sample_app_name to look for published CloudWatch events that match the pattern defined in this rule.
CloudWatch Rules for sample app

CloudWatch rules created for the sample app

CloudWatch alarms

If you did not provide your phone number or email in the JSON file, the sample app uses a CloudWatch alarm named XRayCloudWatchAlarm-sample_app_name in combination with the CloudWatch event that you can use for monitoring.

CloudWatch Alarm for sample app

CloudWatch alarm created for the sample app

Amazon SNS messages

The sample app creates two SNS topics:

  • sample_app_name-cloudwatcheventsnstopic to send out an SMS message when the CloudWatch event matches a pattern published from the Lambda function.
  • sample_app_name-cloudwatchalarmsnstopic to send out an email message when the CloudWatch alarm goes into an ALARM state.
Amazon SNS for sample app

Amazon SNS created for the sample app

Getting notifications

The CloudWatch event looks for the following matching pattern:

  "detail-type": [
    "XCW Notification for Alerts"
  "source": [

The event then invokes an SNS topic that sends out an SMS message.

SMS in sample app

SMS that is sent when CloudWatch Event invokes Amazon SNS topic

The CloudWatch alarm looks for the TriggeredRules metric that is published whenever the CloudWatch event matches the event pattern. It goes into the ALARM state whenever TriggeredRules > 0 for the specified evaluation period and invokes an SNS topic that sends an email message.

Email sent in sample app

Email that is sent when CloudWatch Alarm goes to ALARM state

Stopping notifications

If you provided your phone number or email address, but would like to stop getting notified, change the SUBSCRIBE_TO_EMAIL_SMS environment variable in the Lambda function to No. Then, go to the Amazon SNS console and delete the subscriptions. You can still monitor your application for elevated levels of latency, errors, and faults by using the CloudWatch console.

Lambda environment variable in sample app

Change environment variable in Lambda


Delete subscription in SNS for sample app

Delete subscriptions to stop getting notified

Uninstalling the sample app

To uninstall the sample app, run the script in the Setup folder.

Extending the sample app

The sample app notifes you when when X-Ray detects high latency, errors, and faults in your application. You can extend it to provide more value for your use cases (for example, to perform an action on a resource when the state of a CloudWatch alarm changes).

To summarize, after this set up you will be able to get notified through Amazon SNS when X-Ray detects high latency, errors and faults in your application.

I hope you found this information about setting up alarms and alerts for your application in AWS X-Ray helpful. Feel free to leave questions or other feedback in the comments. Feel free to learn more about AWS X-Ray, Amazon SNS and Amazon CloudWatch

About the Author

Bharath Kumar is a Sr.Product Manager with AWS X-Ray. He has developed and launched mobile games, web applications on microservices and serverless architecture.