GitAuto: [Sentry] Express is not instrumented. This is likely because you required/imported express before calling Sentry.init()

[gitauto-ai]

Resolves #17

Why the bug occurs

When building Node.js applications with bundling tools like esbuild (used by frameworks such as NX), Sentry's auto-instrumentation for frameworks like Express does not work as expected. This is because Sentry relies on intercepting module imports using require hooks to instrument frameworks before they are imported and used by the application. Bundling tools often inline modules and change the load order, preventing Sentry from intercepting the imports as intended. As a result, even if Sentry.init() is called before importing Express in the source code, the bundled output may import Express before Sentry has a chance to instrument it.

This leads to the warning message:

[Sentry] Express is not instrumented. This is likely because you required/imported express before calling `Sentry.init()`

And it prevents Sentry from fully instrumenting Express, missing valuable performance data such as route parameters and middleware spans.

How to reproduce

1. Set up an NX Express application:

   • Use the NX framework to create a new Express application.
   • Install @sentry/node version 8.0.0 or later.

2. Initialize Sentry in your main.ts:

   • Call Sentry.init() before importing Express, following the Sentry documentation.
   • Example main.ts:

     import * as Sentry from '@sentry/node';
     
     Sentry.init({
       dsn: 'your-dsn',
       tracesSampleRate: 1.0,
       // other options...
     });
     
     import express from 'express';
     const app = express();
     
     // ... set up your Express app ...
     
     Sentry.setupExpressErrorHandler(app);

3. Build the application using NX with esbuild:

   • Run nx build your-app to bundle the application using esbuild.

4. Run the bundled application:

   • Start the application with node ./dist/main.js.

5. Observe the warning message:

   • The console outputs the warning:

     [Sentry] Express is not instrumented. This is likely because you required/imported express before calling `Sentry.init()`
     

How to fix

To fix this issue, we need to ensure that Sentry can instrument Express even when the application is bundled with tools like esbuild. There are two main approaches:

Option 1: Externalize Express in the Bundler Configuration

Modify the esbuild configuration to treat express (and any other modules Sentry needs to instrument) as external dependencies. This ensures that express is not bundled and remains a separate module that can be required at runtime, allowing Sentry to instrument it properly.

Steps:

1. Update project.json or build configuration:

   Add the external option to the esbuildOptions:

   {
     "options": {
       // ... other options ...
       "esbuildOptions": {
         // ... other esbuild options ...
         "external": ["express"]
       }
     }
   }

2. Rebuild the application:

   Run nx build your-app to rebuild the application with the updated configuration.

3. Re-run the application:

   Start the application again and verify that the warning message is no longer displayed, and Sentry properly instruments Express.

Explanation:

By externalizing express, esbuild will not bundle it into the application's output. Instead, it will be required at runtime, preserving the require hooks that Sentry relies on for instrumentation.

Option 2: Manually Instrument Express

If externalizing modules is not feasible or desirable, we can enhance the Sentry SDK to allow manual instrumentation of Express. This involves adding a method to the SDK that instruments Express explicitly, regardless of import order or bundling.

Proposed Changes to the Sentry SDK:

1. Add a manual instrumentation method:

   // In Sentry SDK code (e.g., packages/node/src/sdk.ts)
   export function instrumentExpress(): void {
     try {
       const express = require('express');
       const { instrument } = require('@sentry/integrations/build/cjs/express');
       if (express && !express.__sentry_instrumented__) {
         instrument(express);
         express.__sentry_instrumented__ = true;
       }
     } catch (e) {
       __DEBUG_BUILD__ && logger.warn('Failed to instrument Express:', e);
     }
   }

2. Instruct users to call Sentry.instrumentExpress():

   Update the documentation to guide users to call this method after Sentry.init().

   Updated main.ts:

   import * as Sentry from '@sentry/node';
   
   Sentry.init({
     dsn: 'your-dsn',
     tracesSampleRate: 1.0,
     // other options...
   });
   
   // Manually instrument Express
   Sentry.instrumentExpress();
   
   import express from 'express';
   const app = express();
   
   // ... set up your Express app ...
   
   Sentry.setupExpressErrorHandler(app);

Explanation:

This method attempts to require express and instrument it directly. By calling Sentry.instrumentExpress() after Sentry.init(), we ensure that Express is instrumented regardless of bundling or import order.

Benefits:

• Flexibility: Allows applications bundled with esbuild or other tools to use Sentry's Express instrumentation without modifying their bundler configuration.
• Ease of Use: Users can resolve the issue by adding a single method call.
• Better Instrumentation: Enables full Express instrumentation, including route parameters and middleware spans.

Considerations:

• Error Handling: The method includes a try-catch block to handle cases where express is not installed or available.
• Documentation: Update the Sentry documentation to include instructions for manual instrumentation when using bundlers.

---

By implementing one of these fixes, we can resolve the issue where Sentry fails to instrument Express in bundled applications, providing better performance monitoring and user experience.

Test these changes locally

git checkout -b gitauto/issue-#17-f6d6d425-73f4-4ad0-86ba-3d3d28b2886e
git pull origin gitauto/issue-#17-f6d6d425-73f4-4ad0-86ba-3d3d28b2886e