Activities and Failure Semantics

Retries, the four timeouts, heartbeats, and why an Activity can run twice

Activities are the boundary between Workflow code and the outside world. A Worker can die after the side effect and before the completion, so Temporal may run the Activity again: assume every Activity can execute more than once — Temporal guarantees durable orchestration, not exactly-once execution of your effect. You trigger each of the four timeouts on purpose, add a heartbeat to a long Activity, and design an idempotent tool call for an LLM agent.

Estimated time: 105 minutes

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