Cron Scheduling

Comparable to: node-cron, APScheduler, crontab

Key Concepts

Use the concepts below when they fit the task. Not every scheduled job needs all of them.

• Cron expressions use a 7-field format: second minute hour day month weekday year
• CronModule evaluates expressions and fires triggers on schedule
• Handlers should be fast — enqueue heavy work to a queue instead of blocking the cron handler
• Each cron trigger binds one expression to one function
• Overlapping schedules are fine; each trigger fires independently

Architecture

CronModule timer tick
  → registerTrigger type:'cron' expression match
    → registerFunction handler
      → (optional) TriggerAction.Enqueue for heavy work

iii Primitives Used

Primitive	Purpose
registerFunction	Define the handler for the scheduled job
registerTrigger({ type: 'cron' })	Bind a cron expression to a function
config: { expression: '0 0 9 * * * *' }	Cron schedule in 7-field format

Reference Implementation

See ../references/cron-scheduling.js for the full working example — a recurring scheduled task that fires on a cron expression and optionally enqueues heavy work.

Also available in Python: ../references/cron-scheduling.py

Also available in Rust: ../references/cron-scheduling.rs

Common Patterns

Code using this pattern commonly includes, when relevant:

• registerWorker(url, { workerName }) — worker initialization
• registerFunction(id, handler) — define the scheduled handler
• registerTrigger({ type: 'cron', config: { expression } }) — bind the schedule
• trigger({ function_id, payload, action: TriggerAction.Enqueue({ queue }) }) — offload heavy work
• const logger = new Logger() — structured logging per job

Adapting This Pattern

Use the adaptations below when they apply to the task.

• Adjust the 7-field expression to match your schedule (e.g. 0 0 */6 * * * * for every 6 hours)
• Keep the cron handler lightweight — use it to validate and enqueue, not to do the heavy lifting
• For jobs that need state (e.g. last-run timestamp), combine with iii-state-management
• Multiple cron triggers can feed the same queue for fan-in processing

Engine Configuration

CronModule must be enabled in iii-config.yaml. See ../references/iii-config.yaml for the full annotated config reference.

Pattern Boundaries

• If the task is about one-off async work rather than recurring schedules, prefer iii-queue-processing.
• If the trigger should fire on state changes rather than time, prefer iii-state-reactions.
• Stay with iii-cron-scheduling when the primary need is time-based periodic execution.

When to Use

• Use this skill when the task is primarily about iii-cron-scheduling in the iii engine.
• Triggers when the request directly asks for this pattern or an equivalent implementation.

Boundaries

• Never use this skill as a generic fallback for unrelated tasks.
• You must not apply this skill when a more specific iii skill is a better fit.
• Always verify environment and safety constraints before applying examples from this skill.