Configuring the X-Ray SDK for Node.js

You can configure the X-Ray SDK for Node.js with plugins to include information about the service that your application runs on, modify the default sampling behavior, or add sampling rules that apply to requests to specific paths.

Service plugins

Use plugins to record information about the service hosting your application.

To use a plugin, configure the X-Ray SDK for Node.js client by using the config method.

var AWSXRay = require('aws-xray-sdk');
AWSXRay.config([AWSXRay.plugins.EC2Plugin,AWSXRay.plugins.ElasticBeanstalkPlugin]);

The SDK also uses plugin settings to set the origin field on the segment. This indicates the type of AWS resource that runs your application. When you use multiple plugins, the SDK uses the following resolution order to determine the origin: ElasticBeanstalk > EKS > ECS > EC2.

Sampling rules

The SDK uses the sampling rules you define in the X-Ray console to determine which requests to record. The default rule traces the first request each second, and five percent of any additional requests across all services sending traces to X-Ray. Create additional rules in the X-Ray console to customize the amount of data recorded for each of your applications.

The SDK applies custom rules in the order in which they are defined. If a request matches multiple custom rules, the SDK applies only the first rule.

You can also configure the SDK to load sampling rules from a JSON document. The SDK can use local rules as a backup for cases where X-Ray sampling is unavailable, or use local rules exclusively.

{
  "version": 2,
  "rules": [
    {
      "description": "Player moves.",
      "host": "*",
      "http_method": "*",
      "url_path": "/api/move/*",
      "fixed_target": 0,
      "rate": 0.05
    }
  ],
  "default": {
    "fixed_target": 1,
    "rate": 0.1
  }
}

This example defines one custom rule and a default rule. The custom rule applies a five-percent sampling rate with no minimum number of requests to trace for paths under /api/move/. The default rule traces the first request each second and 10 percent of additional requests.

The disadvantage of defining rules locally is that the fixed target is applied by each instance of the recorder independently, instead of being managed by the X-Ray service. As you deploy more hosts, the fixed rate is multiplied, making it harder to control the amount of data recorded.

On AWS Lambda, you cannot modify the sampling rate. If your function is called by an instrumented service, calls that generated requests that were sampled by that service will be recorded by Lambda. If active tracing is enabled and no tracing header is present, Lambda makes the sampling decision.

To configure backup rules, tell the X-Ray SDK for Node.js to load sampling rules from a file with setSamplingRules.

var AWSXRay = require('aws-xray-sdk');
AWSXRay.middleware.setSamplingRules('sampling-rules.json');

You can also define your rules in code and pass them to setSamplingRules as an object.

var AWSXRay = require('aws-xray-sdk');
var rules = {
  "rules": [ { "description": "Player moves.", "service_name": "*", "http_method": "*", "url_path": "/api/move/*", "fixed_target": 0, "rate": 0.05 } ],
  "default": { "fixed_target": 1, "rate": 0.1 },
  "version": 1
  }

AWSXRay.middleware.setSamplingRules(rules);

To use only local rules, call disableCentralizedSampling.

AWSXRay.middleware.disableCentralizedSampling()

Logging

To log output from the SDK, call AWSXRay.setLogger(logger), where logger is an object that provides standard logging methods (warn, info, etc.).

By default the SDK will log error messages to the console using the standard methods on the console object. The log level of the built-in logger can be set by using either the AWS_XRAY_DEBUG_MODE or AWS_XRAY_LOG_LEVEL environment variables. For a list of valid log level values, see Environment variables.

If you wish to provide a different format or destination for the logs then you can provide the SDK with your own implementation of the logger interface as shown below. Any object that implements this interface can be used. This means that many logging libraries, e.g. Winston, could be used and passed to the SDK directly.

var AWSXRay = require('aws-xray-sdk');

// Create your own logger, or instantiate one using a library.
var logger = {
  error: (message, meta) => { /* logging code */ },
  warn: (message, meta) => { /* logging code */ },
  info: (message, meta) => { /* logging code */ },
  debug: (message, meta) => { /* logging code */ }
}

AWSXRay.setLogger(logger);
AWSXRay.config([AWSXRay.plugins.EC2Plugin]);

Call setLogger before you run other configuration methods to ensure that you capture output from those operations.

X-Ray daemon address

If the X-Ray daemon listens on a port or host other than 127.0.0.1:2000, you can configure the X-Ray SDK for Node.js to send trace data to a different address.

AWSXRay.setDaemonAddress('host:port');

You can specify the host by name or by IPv4 address.

var AWSXRay = require('aws-xray-sdk');
AWSXRay.setDaemonAddress('daemonhost:8082');

If you configured the daemon to listen on different ports for TCP and UDP, you can specify both in the daemon address setting.

var AWSXRay = require('aws-xray-sdk');
AWSXRay.setDaemonAddress('tcp:daemonhost:8082 udp:daemonhost:8083');

You can also set the daemon address by using the AWS_XRAY_DAEMON_ADDRESS environment variable.

Environment variables

You can use environment variables to configure the X-Ray SDK for Node.js. The SDK supports the following variables.