From cafba2d789cf954000f2ad0e1c6a7828894adf2c Mon Sep 17 00:00:00 2001
From: Joey Zhao <5253430+joeyzhao2018@users.noreply.github.com>
Date: Fri, 24 Jul 2026 15:28:05 -0400
Subject: [PATCH 1/2] feat(handler): register dd-trace ESM loader hook
 programmatically

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.
---
 src/handler.mjs | 35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/src/handler.mjs b/src/handler.mjs
index 8e6ea3db0..b7e875a03 100644
--- a/src/handler.mjs
+++ b/src/handler.mjs
@@ -1,3 +1,6 @@
+import * as Module from "module";
+import { dirname } from "path";
+import { pathToFileURL } from "url";
 import {
   datadog,
   datadogHandlerEnvVar,
@@ -15,8 +18,38 @@ if (process.env.DD_TRACE_DISABLED_PLUGINS === undefined) {
   logDebug("disabled the dd-trace plugin 'fs'");
 }
 
+// True when dd-trace's ESM loader hook is already active via NODE_OPTIONS or
+// execArgv (e.g. the standard ESM setup: NODE_OPTIONS=--import dd-trace/initialize.mjs).
+// module.register() does not dedupe — a second registration chains another hooks
+// worker and every module would be rewritten twice.
+function esmLoaderAlreadyRegistered() {
+  const sources = [process.env.NODE_OPTIONS || "", ...process.execArgv];
+  return sources.some((source) => /dd-trace[\\/][^\s]*\.mjs/.test(source));
+}
+
 if (getEnvValue("DD_TRACE_ENABLED", "true").toLowerCase() === "true") {
-  initTracer();
+  const tracer = initTracer();
+
+  // Register dd-trace's ESM loader hooks programmatically so that ESM imports
+  // (e.g. @aws/durable-execution-sdk-js) are rewritten for instrumentation.
+  // Normally this happens via --import dd-trace/initialize.mjs, but the AWS
+  // durable runtime ignores NODE_OPTIONS so the loader is never registered.
+  // This mirrors what dd-trace/initialize.mjs does at lines 77-84, including
+  // only registering when the tracer initialized — a bail-out leaves the hooks
+  // worker with nothing to instrument and can keep the process from exiting.
+  if (tracer && typeof Module.register === "function" && !esmLoaderAlreadyRegistered()) {
+    try {
+      const require = Module.createRequire(import.meta.url);
+      const ddTraceEntry = require.resolve("dd-trace", {
+        paths: ["/var/task/node_modules", ...(require.resolve.paths("dd-trace") || [])],
+      });
+      const ddTraceRoot = pathToFileURL(dirname(ddTraceEntry) + "/").href;
+      Module.register("./loader-hook.mjs", ddTraceRoot);
+      logDebug("registered dd-trace ESM loader hook for ESM instrumentation");
+    } catch (error) {
+      logDebug("failed to register dd-trace ESM loader hook", { error });
+    }
+  }
 }
 
 const taskRootEnv = getEnvValue(lambdaTaskRootEnvVar, "");

From 8259c898ba27f98388111c88fe229b4cb60619a0 Mon Sep 17 00:00:00 2001
From: Joey Zhao <5253430+joeyzhao2018@users.noreply.github.com>
Date: Tue, 28 Jul 2026 11:45:33 -0400
Subject: [PATCH 2/2] fix(handler): detect dd-trace/register.js in ESM loader
 dedupe guard

--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.
---
 src/handler.mjs | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/handler.mjs b/src/handler.mjs
index b7e875a03..ae5860104 100644
--- a/src/handler.mjs
+++ b/src/handler.mjs
@@ -19,12 +19,15 @@ if (process.env.DD_TRACE_DISABLED_PLUGINS === undefined) {
 }
 
 // True when dd-trace's ESM loader hook is already active via NODE_OPTIONS or
-// execArgv (e.g. the standard ESM setup: NODE_OPTIONS=--import dd-trace/initialize.mjs).
+// execArgv. Covers every preload entry point that registers the hook:
+//   --import dd-trace/initialize.mjs  (documented ESM setup)
+//   --loader dd-trace/initialize.mjs  (legacy)
+//   --require dd-trace/register.js    (documented CJS setup; also registers the hook)
 // module.register() does not dedupe — a second registration chains another hooks
 // worker and every module would be rewritten twice.
 function esmLoaderAlreadyRegistered() {
   const sources = [process.env.NODE_OPTIONS || "", ...process.execArgv];
-  return sources.some((source) => /dd-trace[\\/][^\s]*\.mjs/.test(source));
+  return sources.some((source) => /dd-trace[\\/](?:[^\s]*\.mjs|register\.js)/.test(source));
 }
 
 if (getEnvValue("DD_TRACE_ENABLED", "true").toLowerCase() === "true") {