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Solutions to errors you may hit while running the iii engine and workers.

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KVM not accessible

Workers boot inside a microVM that needs read/write access to /dev/kvm. On Linux hosts where your user is not in the kvm group (common on WSL2), starting a worker fails with KVM not accessible. Add your user to the kvm group:
Then restart your session so the new group membership applies. On WSL2, run wsl --shutdown from a Windows terminal and reopen your distribution.
For why workers run in microVMs, see Engine.

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An observer’s target never runs

List the observers of the observed function:
Find yours by its target and read its state:
  • pending or error: reason says why, for example the owner has not acknowledged it, the target is not registered, or the args were refused (INVALID_ARGS). See Observer states.
  • active with fires and dropped at 0: no event has reached it. Check delivery:
    • owner: the observer gets an event only when the function’s code calls obs.emit or obs.call on it. Inside onObserverAdded, the observer is not active yet, so these calls do not deliver. See Advanced function observation with owner delivery.
    • auto: only invocations that start after the observer turned active, end with the outcome its on asks for (success by default), and pass its filters are events. A call already running when the observer turned active is not one, so call the function again.
  • dropped or activation_failures above 0: events reached it and were dropped or failed, counted by reason (OVERFLOW, LOOP_GUARD, …).

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Logger lines do not show up

Logger sends its lines to the engine. They do not appear in your worker’s output. Look in the engine’s output (under iii compose --up, .iii/compose/<namespace>/engine.log), or run:
If they are not there either, the worker’s OpenTelemetry export may be off (OTEL_ENABLED=false). Logger then falls back to the language’s own logging, which the Rust SDK prints only with a tracing subscriber. See Where the lines go.