Configuring the X-Ray SDK for Go

You can specify the configuration for X-Ray SDK for Go through environment variables, by calling Configure with a Config object, or by assuming default values. Environment variables take precedence over Config values, which take precedence over any default value.

Service plugins

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

Plugins

• Amazon EC2 – EC2Plugin adds the instance ID, Availability Zone, and the CloudWatch Logs Group.

• Elastic Beanstalk – ElasticBeanstalkPlugin adds the environment name, version label, and deployment ID.

• Amazon ECS – ECSPlugin adds the container ID.

To use a plugin, import one of the following packages.

"github.com/aws/aws-xray-sdk-go/awsplugins/ec2"
"github.com/aws/aws-xray-sdk-go/awsplugins/ecs"
"github.com/aws/aws-xray-sdk-go/awsplugins/beanstalk"

Each plugin has an explicit Init() function call that loads the plugin.

Example ec2.Init()

import (
	"os"

	"github.com/aws/aws-xray-sdk-go/awsplugins/ec2"
	"github.com/aws/aws-xray-sdk-go/xray"
)

func init() {
  // conditionally load plugin
  if os.Getenv("ENVIRONMENT") == "production" {
    ec2.Init()
  }

  xray.Configure(xray.Config{
    ServiceVersion: "1.2.3",
  })
}

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.

Note

If the SDK can't reach X-Ray to get sampling rules, it reverts to a default local rule of the first request each second, and five percent of any additional requests per host. This can occur if the host doesn't have permission to call sampling APIs, or can't connect to the X-Ray daemon, which acts as a TCP proxy for API calls made by the SDK.

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.

Example sampling-rules.json

{
  "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 provide backup rules, point to the local sampling JSON file by using NewCentralizedStrategyWithFilePath.

Example main.go – Local sampling rule

s, _ := sampling.NewCentralizedStrategyWithFilePath("sampling.json") // path to local sampling json
xray.Configure(xray.Config{SamplingStrategy: s})

To use only local rules, point to the local sampling JSON file by using NewLocalizedStrategyFromFilePath.

Example main.go – Disable sampling

s, _ := sampling.NewLocalizedStrategyFromFilePath("sampling.json") // path to local sampling json
xray.Configure(xray.Config{SamplingStrategy: s})

Logging

Note

The xray.Config{} fields LogLevel and LogFormat are deprecated starting with version 1.0.0-rc.10.

X-Ray uses the following interface for logging. The default logger writes to stdout at LogLevelInfo and above.

type Logger interface {
	Log(level LogLevel, msg fmt.Stringer)
}

const (
	LogLevelDebug LogLevel = iota + 1
	LogLevelInfo
	LogLevelWarn
	LogLevelError
)

Example write to io.Writer

xray.SetLogger(xraylog.NewDefaultLogger(os.Stderr, xraylog.LogLevelError))

Environment variables

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

• AWS_XRAY_CONTEXT_MISSING – Set to RUNTIME_ERROR to throw exceptions when your instrumented code attempts to record data when no segment is open.

  Valid Values

  • RUNTIME_ERROR – Throw a runtime exception.

  • LOG_ERROR – Log an error and continue (default).

  • IGNORE_ERROR – Ignore error and continue.

  Errors related to missing segments or subsegments can occur when you attempt to use an instrumented client in startup code that runs when no request is open, or in code that spawns a new thread.

• AWS_XRAY_TRACING_NAME – Set the service name that the SDK uses for segments.

• AWS_XRAY_DAEMON_ADDRESS – Set the host and port of the X-Ray daemon listener. By default, the SDK sends trace data to 127.0.0.1:2000. Use this variable if you have configured the daemon to listen on a different port or if it is running on a different host.

• AWS_XRAY_CONTEXT_MISSING – Set the value to determine how the SDK handles missing context errors. Errors related to missing segments or subsegments can occur when you attempt to use an instrumented client in the startup code when no request is open, or in code that spawns a new thread.

  • RUNTIME_ERROR – By default, the SDK is set to throw a runtime exception.

  • LOG_ERROR – Set to log an error and continue.

Environment variables override equivalent values set in code.

Using configure

You can also configure the X-Ray SDK for Go using the Configure method. Configure takes one argument, a Config object, with the following, optional fields.

DaemonAddr

This string specifies the host and port of the X-Ray daemon listener. If not specified, X-Ray uses the value of the AWS_XRAY_DAEMON_ADDRESS environment variable. If that value is not set, it uses "127.0.0.1:2000".

ServiceVersion

This string specifies the version of the service. If not specified, X-Ray uses the empty string ("").

SamplingStrategy

This SamplingStrategy object specifies which of your application calls are traced. If not specified, X-Ray uses a LocalizedSamplingStrategy, which takes the strategy as defined in xray/resources/DefaultSamplingRules.json.

StreamingStrategy

This StreamingStrategy object specifies whether to stream a segment when RequiresStreaming returns true. If not specified, X-Ray uses a DefaultStreamingStrategy that streams a sampled segment if the number of subsegments is greater than 20.

ExceptionFormattingStrategy

This ExceptionFormattingStrategy object specifies how you want to handle various exceptions. If not specified, X-Ray uses a DefaultExceptionFormattingStrategy with an XrayError of type error, the error message, and stack trace.