Instrumentation

Next runs one instrumentation.ts per server. With zones there is one server and several apps, so next-zones dispatches.

	`register()`	`onRequestError()`
The shell's	once, when the server starts	for errors on every route, any zone's included (unless the policy skips a zone)
A zone's own	when that zone image is installed	for errors on that zone's routes only

A zone never sees another zone's errors.

The policy#

zones.config.json, in the workspace's folder (beside the zones' folders), read by next-zones start, serve, zones.js and mode "single" (see the CLI); or createZones({ policy }) with the same object:

{
  "instrumentation": {
    "shell": { "skip": ["shop"] },
    "own": { "blog": false }
  }
}

shell.skip: zones whose errors do not go to the shell's onRequestError.
own: set a zone to false to turn off its own instrumentation. By default every zone's runs.

Things to know#

register() is process-wide. All zones run in one Node process, so whatever a register() sets globally (an OpenTelemetry tracer provider, process.on handlers) affects every zone. Keep global setup in the shell, and let a zone's register() do only zone-scoped work.
Swapping a version. Next has no "unregister". If a zone exports unregister(), next-zones calls it on the version being replaced, before the new version's register().

The same in both modes: on Zones, and in mode "single", where next-zones writes the one app's instrumentation file to dispatch this way. A zone's register() runs when Zones installs its image, or, in one app, when that app starts.

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