Webpack bundles all the source code, including dependencies, into a single JS file. Node.js usually loads modules through CommonJS, which means that dependencies are loaded using require functions (for example, require("express")). OpenTelemetry only supports CommonJS, as it injects itself into the require calls and intercepts loaded modules. With Webpack, require calls are compiled out, as all of the source code lives in a single bundle file and Webpack's internal module loading is used after copying the code. Thus OpenTelemetry, nor any other instrumentation SDKs, cannot instrument Webpack's internal modules.
The workaround for Webpack 4 is located here.
To get tracing to work using OpenTelemetry, you need to retain the require calls. You can do this using Webpack's externals configuration option. When modules are loaded and Webpack encounters a module in the externals list, it won't copies and pastes the source code to the final bundle file. Dependencies listed in externals need to be available in node_modules for require to find them.
Consider we are using express and want to instrument it using @opentelemetry/instrumentation-express. You'd need to add the following to webpack.config.js:
externalsType: "node-commonjs",
externals: [
"express"
]Webpack will now load express using the require method.
See webpack.config.js for a complete list.
Note: When using instrumentations targeting Node.js code modules, such as
http,net, anddns, you don't need to add them toexternals.
npm install
npm run compile
npm run start
curl localhost:7000/foo
If you have the Splunk OpenTelemetry Collector running, you should now see spans from http, dns, express, and ioredis instrumentations.