Developer Guide

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Tracing Incoming Requests with the X-Ray SDK for Node.js

You can use the X-Ray SDK for Node.js to trace incoming HTTP requests that your Express and Restify applications serve on an EC2 instance in Amazon EC2, AWS Elastic Beanstalk, or Amazon ECS.

The X-Ray SDK for Node.js provides middleware for applications that use the Express and Restify frameworks. When you add the X-Ray middleware to your application, the X-Ray SDK for Node.js creates a segment for each sampled request. This segment includes timing, method, and disposition of the HTTP request. Additional instrumentation creates subsegments on this segment.


For AWS Lambda functions, Lambda creates a segment for each sampled request. See AWS Lambda and AWS X-Ray for more information.

Each segment has a name that identifies your application in the service map. The segment can be named statically, or you can configure the SDK to name it dynamically based on the host header in the incoming request. Dynamic naming lets you group traces based on the domain name in the request, and apply a default name if the name doesn't match an expected pattern (for example, if the host header is forged).

Forwarded Requests

If a load balancer or other intermediary forwards a request to your application, X-Ray takes the client IP from the X-Forwarded-For header in the request instead of from the source IP in the IP packet. The client IP that is recorded for a forwarded request can be forged, so it should not be trusted.

When a request is forwarded, the SDK sets an additional field in the segment to indicate this. If the segment contains the field x_forwarded_for set to true, the client IP was taken from the X-Forwarded-For header in the HTTP request.

The message handler creates a segment for each incoming request with an http block that contains the following information:

  • HTTP method – GET, POST, PUT, DELETE, etc.

  • Client address – The IP address of the client that sent the request.

  • Response code – The HTTP response code for the completed request.

  • Timing – The start time (when the request was received) and end time (when the response was sent).

  • User agent — The user-agent from the request.

  • Content length — The content-length from the response.

Tracing Incoming Requests with Express

To use the Express middleware, initialize the SDK client and use the middleware returned by the express.openSegment function before you define your routes.

Example app.js - Express

var app = express(); var AWSXRay = require('aws-xray-sdk'); app.use('MyApp')); app.get('/', function (req, res) { res.render('index'); }); app.use(;

After you define your routes, use the output of express.closeSegment as shown to handle any errors returned by the X-Ray SDK for Node.js.

Tracing Incoming Requests with Restify

To use the Restify middleware, initialize the SDK client and run enable. Pass it your Restify server and segment name.

Example app.js - Restify

var AWSXRay = require('aws-xray-sdk'); var AWSXRayRestify = require('aws-xray-sdk-restify'); var restify = require('restify'); var server = restify.createServer(); AWSXRayRestify.enable(server, 'MyApp')); server.get('/', function (req, res) { res.render('index'); });

Configuring a Segment Naming Strategy

AWS X-Ray uses a service name to identify your application and distinguish it from the other applications, databases, external APIs, and AWS resources that your application uses. When the X-Ray SDK generates segments for incoming requests, it records your application's service name in the segment's name field.

The X-Ray SDK can name segments after the hostname in the HTTP request header. However, this header can be forged, which could result in unexpected nodes in your service map. To prevent the SDK from naming segments incorrectly due to requests with forged host headers, you must specify a default name for incoming requests.

If your application serves requests for multiple domains, you can configure the SDK to use a dynamic naming strategy to reflect this in segment names. A dynamic naming strategy allows the SDK to use the hostname for requests that match an expected pattern, and apply the default name to requests that don't.

For example, you might have a single application serving requests to three subdomains–,, and You can use a dynamic naming strategy with the pattern * to identify segments for each subdomain with a different name, resulting in three service nodes on the service map. If your application receives requests with a hostname that doesn't match the pattern, you will see a fourth node on the service map with a fallback name that you specify.

To use the same name for all request segments, specify the name of your application when you initialize the middleware, as shown in the previous sections.


You can override the default service name that you define in code with the AWS_XRAY_TRACING_NAME environment variable.

A dynamic naming strategy defines a pattern that hostnames should match, and a default name to use if the hostname in the HTTP request does not match the pattern. To name segments dynamically, use AWSXRay.middleware.enableDynamicNaming.

Example app.js - Dynamic Segment Names

If the hostname in the request matches the pattern *, use the hostname. Otherwise, use MyApp.

var app = express(); var AWSXRay = require('aws-xray-sdk'); app.use('MyApp')); AWSXRay.middleware.enableDynamicNaming('*'); app.get('/', function (req, res) { res.render('index'); }); app.use(;