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Amazon X-Ray auto-instrumentation agent for Java

The Amazon X-Ray auto-instrumentation agent for Java is a tracing solution that instruments your Java web applications with minimal development effort. The agent enables tracing for servlet-based applications and all of the agent's downstream requests made with supported frameworks and libraries. This includes downstream Apache HTTP requests, Amazon SDK requests, and SQL queries made using a JDBC driver. The agent propagates X-Ray context, including all active segments and subsegments, across threads. All of the configurations and versatility of the X-Ray SDK are still available with the Java agent. Suitable defaults were chosen to ensure that the agent works with minimal effort.

The X-Ray agent solution is best suited for servlet-based, request-response Java web application servers. If your application uses an asynchronous framework, or is not well modeled as a request-response service, you might want to consider manual instrumentation with the SDK instead. 

The X-Ray agent is built using the Distributed Systems Comprehension toolkit, or DiSCo. DiSCo is an open source framework for building Java agents that can be used in distributed systems. While it is not necessary to understand DiSCo to use the X-Ray agent, you can learn more about the project by visiting its homepage on GitHub. The X-Ray agent is also fully open-sourced. To view the source code, make contributions, or raise issues about the agent, visit its repository on GitHub.

Sample application

The eb-java-scorekeep sample application is adapted to be instrumented with the X-Ray agent. This branch contains no servlet filter or recorder configuration, as these functions are done by the agent. To run the application locally or using Amazon resources, follow the steps in the sample application's readme file. The instructions for using the sample app to generate X-Ray traces are in the sample app’s tutorial.

Getting started

To get started with the X-Ray auto-instrumentation Java agent in your own application, follow these steps.

Configuration

The X-Ray agent is configured by an external, user-provided JSON file. By default, this file is at the root of the user’s classpath (for example, in their resources directory) named xray-agent.json. You can configure a custom location for the config file by setting the com.amazonaws.xray.configFile system property to the absolute filesystem path of your configuration file.

An example configuration file is shown next.

{     
    "serviceName": "XRayInstrumentedService", 
    "contextMissingStrategy": "LOG_ERROR", 
    "daemonAddress": "127.0.0.1:2000", 
    "tracingEnabled": true, 
    "samplingStrategy": "CENTRAL",     
    "traceIdInjectionPrefix": "prefix",     
    "samplingRulesManifest": "/path/to/manifest",     
    "awsServiceHandlerManifest": "/path/to/manifest",     
    "awsSdkVersion": 2,     
    "maxStackTraceLength": 50,     
    "streamingThreshold": 100,     
    "traceIdInjection": true,     
    "pluginsEnabled": true,     
    "collectSqlQueries": false 
}

Configuration specification

The following table describes valid values for each property. Property names are case sensitive, but their keys are not. For properties that can be overridden by environment variables and system properties, the order of priority is always environment variable, then system property, and then configuration file. For information about properties that you can override, see Environment variables. All fields are optional.

Logging configuration

The X-Ray agent's log level can be configured in the same way as the X-Ray SDK for Java. See Logging for more information on configuring logging with the X-Ray SDK for Java.

Manual instrumentation

If you’d like to perform manual instrumentation in addition to the agent’s auto-instrumentation, add the X-Ray SDK as a dependency to your project. Note that the SDK's custom servlet filters mentioned in Tracing Incoming Requests are not compatible with the X-Ray agent.

If you are working in a Maven project, add the following dependencies to your pom.xml file.

<dependencies> 
  <dependency> 
    <groupId>com.amazonaws</groupId> 
    <artifactId>aws-xray-recorder-sdk-core</artifactId> 
    <version>2.11.0</version> 
  </dependency> 
  </dependencies>

If you are working in a Gradle project, add the following dependencies to your build.gradle file.

implementation 'com.amazonaws:aws-xray-recorder-sdk-core:2.11.0' 

You can add custom subsegments in addition to annotations, metadata, and user IDs while using the agent, just as you would with the normal SDK. The agent automatically propagates context across threads, so no workarounds to propagate context should be necessary when working with multithreaded applications.

Troubleshooting

Since the agent offers fully automatic instrumentation, it can be difficult to identify the root cause of a problem when you are experiencing issues. If the X-Ray agent is not working as expected for you, review the following problems and solutions. The X-Ray agent and SDK use Jakarta Commons Logging (JCL). To see the logging output, ensure that a bridge connecting JCL to your logging backend is on the classpath, as in the following example: log4j-jcl or jcl-over-slf4j.

Problem: I’ve enabled the Java agent on my application but don’t see anything on the X-Ray console

Is the X-Ray daemon running on the same machine?

If not, see the X-Ray daemon documentation to set it up.

In your application logs, do you see a message like "Initializing the X-Ray agent recorder"?

If you have correctly added the agent to your application, this message is logged at INFO level when your application starts, before it starts taking requests. If this message is not there, then the Java agent is not running with your Java process. Make sure you’ve followed all the setup steps correctly with no typos.

In your application logs, do you see several error messages saying something like "Suppressing Amazon X-Ray context missing exception"?

These errors occur because the agent is trying to instrument downstream requests, like Amazon SDK requests or SQL queries, but the agent was unable to automatically create a segment. If you see many of these errors, the agent might not be the best tool for your use case and you might want to consider manual instrumentation with the X-Ray SDK instead. Alternatively, you can enable X-Ray SDK debug logs to see the stack trace of where the context-missing exceptions are occurring. You can wrap these portions of your code with custom segments, which should resolve these errors. For an example of wrapping downstream requests with custom segments, see the sample code in instrumenting startup code.

Problem: Some of the segments I expect do not appear on the X-Ray console

Does your application use multithreading?

If some segments that you expect to be created are not appearing in your console, background threads in your application might be the cause. If your application performs tasks using background threads that are “fire and forget,” like making a one-off call to a Lambda function with the Amazon SDK, or polling some HTTP endpoint periodically, that may confuse the agent while it is propagating context across threads. To verify this is your problem, enable X-Ray SDK debug logs and check for messages like: Not emitting segment named <NAME > as it parents in-progress subsegments. To work around this, you can try joining the background threads before your server returns to ensure all the work done in them is recorded. Or, you can set the agent’s contextPropagation configuration to false to disable context propagation in background threads. If you do this, you’ll have to manually instrument those threads with custom segments or ignore the context missing exceptions they produce.

Have you set up sampling rules?

If there are seemingly random or unexpected segments appearing on the X-Ray console, or the segments you expect to be on the console aren’t, you might be experiencing a sampling issue. The X-Ray agent applies centralized sampling to all segments it creates, using the rules from the X-Ray console. The default rule is 1 segment per second, plus 5% of segments afterward, are sampled. This means segments that are created rapidly with the agent might not be sampled. To resolve this, you should create custom sampling rules on the X-Ray console that appropriately sample the desired segments. For more information, see sampling.