Scheduled Functions

"Automate what repeats — schedule what must happen on time." — Unknown

TL;DR

Guides implementation of scheduled Cloud Functions using Firebase's onSchedule with cron patterns — covering batch data processing, cleanup tasks, report generation, and reliable execution with error handling and monitoring. Use when you need periodic server-side tasks that run automatically. [EXPLICIT]

Procedure

Step 1: Discover

• Identify tasks that need periodic execution (cleanup, reports, sync, reminders)
• Check existing scheduled functions and their cron patterns
• Review data volumes for batch processing capacity planning
• Determine timezone requirements for schedule timing

Step 2: Analyze

• Define cron schedule for each task (Cloud Scheduler syntax)
• Plan batch processing strategy for large datasets (pagination, chunking)
• Design idempotency for safe re-execution on failures
• Evaluate timeout limits (Cloud Functions v2: up to 60 minutes)

Step 3: Execute

• Create scheduled function with onSchedule and cron expression
• Implement batch processing with Firestore pagination (process N documents per run)
• Add execution logging: start time, records processed, errors, duration
• Handle timeouts gracefully (checkpoint progress, resume on next run)
• Set up error alerting via Cloud Monitoring
• Use runWith({ timeoutSeconds, memory }) for resource-intensive tasks
• Implement distributed locks if concurrent execution must be prevented

Step 4: Validate

• Test function manually before scheduling (firebase functions:shell)
• Verify cron expression fires at expected times (use crontab.guru)
• Confirm batch processing handles edge cases (empty collections, errors mid-batch)
• Check Cloud Scheduler dashboard for execution history and errors

Quality Criteria

• Cron schedule documented with human-readable explanation
• Batch processing handles large datasets without timeout
• Function is idempotent — safe to re-run without side effects
• Execution results logged for monitoring and debugging
• Evidence tags applied to all claims

Anti-Patterns

• Running expensive queries without pagination (timeout on large collections)
• Not handling function timeout (data left in inconsistent state)
• Scheduling functions too frequently without checking if previous run completed

Related Skills

• cloud-functions — scheduled functions are a specialized Cloud Function trigger
• firebase-extensions — some extensions include scheduled processing

Usage

Example invocations:

• "/scheduled-functions" — Run the full scheduled functions workflow
• "scheduled functions on this project" — Apply to current context

Assumptions & Limits

• Assumes access to project artifacts (code, docs, configs) [EXPLICIT]
• Requires English-language output unless otherwise specified [EXPLICIT]
• Does not replace domain expert judgment for final decisions [EXPLICIT]

Edge Cases

Scenario	Handling
Empty or minimal input	Request clarification before proceeding
Conflicting requirements	Flag conflicts explicitly, propose resolution
Out-of-scope request	Redirect to appropriate skill or escalate