feat(handler): register dd-trace ESM loader hook programmatically - #801
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ESM instrumentation (orchestrion/rewriter-based, e.g. the
@aws/durable-execution-sdk-js integration) depends on dd-trace's
loader-hook.mjs being registered via --import dd-trace/initialize.mjs.
Runtimes that ignore NODE_OPTIONS (e.g. the AWS durable functions
runtime) never register it, so ESM handlers get no rewritten
instrumentation while CJS handlers work.
Mirror what dd-trace/initialize.mjs does: resolve the dd-trace package
root and Module.register('./loader-hook.mjs') from handler.mjs before
the user's ESM handler is imported.
Guards:
- Skip when the loader hook is already active via NODE_OPTIONS/execArgv
(module.register() does not dedupe; a second registration would run
the rewriter twice on every module).
- Skip when the tracer failed to initialize, matching initialize.mjs.
- Use a namespace import for 'module' so runtimes without
module.register (< 18.19 / < 20.6) don't fail at link time.
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--require dd-trace/register.js (and --import of it, which works on modern Node via CJS interop) also registers loader-hook.mjs, but the .mjs-only pattern missed it, causing a second registration and double rewriting. Match register.js alongside .mjs preload entry points.
zarirhamza
approved these changes
Jul 28, 2026
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https://datadoghq.atlassian.net/browse/APMSVLS-587
ESM instrumentation (orchestrion/rewriter-based, e.g. the @aws/durable-execution-sdk-js integration) depends on dd-trace's loader-hook.mjs being registered via --import dd-trace/initialize.mjs. Runtimes that ignore NODE_OPTIONS (e.g. the AWS durable functions runtime (not the regualr lambda runtime)) never register it, so ESM handlers get no rewritten instrumentation while CJS handlers work.
Mirror what dd-trace/initialize.mjs does: resolve the dd-trace package root and Module.register('./loader-hook.mjs') from handler.mjs before the user's ESM handler is imported.
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