No-code Instrumentation for Node.js in Splunk Observability Cloud

No-Code Instrumentation enables distributed tracing in Node.js applications without modifying the source code. Instrumentation is configured declaratively via a JSON file. Spans are generated based on configuration and can include custom attributes extracted from function arguments.

CAUTION: No-code instrumentation is one of the available approaches to integrate with OpenTelemetry.

Configuration File Location

By default, the instrumentation loads its configuration from a file named nocode.config.json in the current working directory. You can override this location using the NOCODE_CONFIG_PATH environment variable:

export NOCODE_CONFIG_PATH=/path/to/your/config.json

Configuration File Structure

The configuration file contains an array of instrumentation definitions. These map to OpenTelemetry's InstrumentationModuleDefinition and InstrumentationFileDefinition objects.

[
  {
    "moduleName": "mynodemodule",
    "supportedVersions": [">=4.0.0"],
    "files": [
      {
        "name": "lib/util.js",
        "methodName": "processData",
        "spanName": "mynodemodule.processData",
        "attributes": [
          {
            "attrIndex": 0,
            "attrPath": "user.id",
            "key": "user.id"
          }
        ]
      }
    ]
  },
  {
    "absolutePath": "/absolute/path/to/your/project/src/utils/helper.js",
    "files": [
      {
        "name": "utils/helper",
        "methodName": "calculateTotal",
        "spanName": "helper.calculateTotal",
        "attributes": [
          {
            "attrIndex": 0,
            "attrPath": "items.length",
            "key": "item.count"
          },
          {
            "attrIndex": 1,
            "attrPath": "options.currency",
            "key": "currency"
          }
        ]
      }
    ]
  }
]

Configuration Properties

To define how specific functions should be traced, the configuration file uses structured objects. Below are the key components and their properties:

Instrumentation definition


Property	Type	Required	Description
moduleName	string	No*	Name of the npm module to instrument (e.g., "express", "lodash")
absolutePath	string	No*	Absolute path to a specific file to instrument
supportedVersions	string[]	No	Supported version ranges (defaults to `["*"]`) — applies only to `moduleName`
mainModuleMethods	array	No	Methods exported directly by the module's main file
files	array	No	List of files and methods to instrument

*Either moduleName or absolutePath must be specified.

Usage Guidelines

To configure no-code instrumentation correctly, follow these simple rules:

Use moduleName when instrumenting code from npm packages (like express or lodash)
Use absolutePath when instrumenting your own project files
Use mainModuleMethods to target functions exported directly by a module
Use files to target functions inside specific files
Use supportedVersions only with moduleName; it has no effect with absolutePath
When using absolutePath, omit file extensions in the name field (e.g. "utils/helper")
When using moduleName, include file extensions in the name field (e.g. "lib/util.js")

Function instrumentation (used in `files` and `mainModuleMethods`)


Property	Type	Required	Description
name	string	Yes	Relative path to the file (only used in `files`)
methodName	string	Yes	Name of the function or method to instrument
spanName	string	No	Custom span name (defaults to the method name)
attributes	Attribute definition[]	No	List of attributes to extract from function arguments

Note:

name is required only when the object is used inside the files array.
When used in mainModuleMethods, name is omitted because the method is exported directly by the module.

Limitations

File-level granularity: Can only instrument functions exported from modules, not internal functions
Static configuration: Configuration is loaded once at startup and cannot be changed at runtime