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Document threads.preload config option #561

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Document threads.preload config option
kriszyp Jul 2, 2026
6df4f08
Split threads.preload YAML into single- and multi-module examples
kriszyp Jul 2, 2026
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15 changes: 15 additions & 0 deletions reference/configuration/options.md
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Expand Up @@ -65,6 +65,21 @@ threads:
- `maxHeapMemory` — Heap limit per thread (MB)
- `heapSnapshotNearLimit` — Write a `.heapsnapshot` file when a thread nears its heap limit (loadable in Chrome DevTools Memory tab); _Default_: `false`. See [Worker Thread Debugging](./debugging.md#heap-snapshots-near-the-limit)
- `debug` — Enable Node.js inspector; sub-options: `port`, `startingPort`, `host`, `waitForDebugger`. See [Worker Thread Debugging](./debugging.md)
- `preload` <VersionBadge version="v5.2.0" /> — Module, or list of modules, to load (via Node's `--require`) before any Harper or application module on each worker thread. Intended for instrumentation/APM agents (e.g. `dd-trace`) that must load first to instrument subsequent module loads. Bare specifiers (e.g. `dd-trace/init`) resolve against the `node_modules` of your installed [components](../components/overview.md) — so the agent can be shipped as a dependency of a deployed component — and absolute paths are also accepted. Applies to worker threads only (not under Bun).

```yaml
threads:
preload: dd-trace/init
```

Or several modules:

```yaml
threads:
preload:
- dd-trace/init
- /opt/instrumentation/agent.js
```

---

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