Instrumentation

Note: This feature is experimental. To use it, you must explicitly opt in by defining experimental.instrumentationHook = true; in your next.config.js.

If you export a function named register from this file, we will call that function whenever a new Next.js server instance is bootstrapped. When your register function is deployed, it will be called on each cold boot (but exactly once in each environment).

Sometimes, it may be useful to import a file in your code because of the side effects it will cause. For example, you might import a file that defines a set of global variables, but never explicitly use the imported file in your code. You would still have access to the global variables the package has declared.

You can import files with side effects in instrumentation.ts, which you might want to use in your register function as demonstrated in the following example:

import { init } from 'package-init';
 
export function register() {
  init();
}

However, we recommend importing files with side effects using import from within your register function instead. The following example demonstrates a basic usage of import in a register function:

export async function register() {
  await import('package-with-side-effect');
}

By doing this, you can colocate all of your side effects in one place in your code, and avoid any unintended consequences from importing files.

We call register in all environments, so it's necessary to conditionally import any code that doesn't support both edge and nodejs. You can use the environment variable NEXT_RUNTIME to get the current environment. Importing an environment-specific code would look like this:

export async function register() {
  if (process.env.NEXT_RUNTIME === 'nodejs') {
    await import('./instrumentation-node');
  }
 
  if (process.env.NEXT_RUNTIME === 'edge') {
    await import('./instrumentation-edge');
  }
}