Definition
AnArcis the minimal viable connection between two systems. Not bidirectional synchronization. Not complex transformation pipelines. Just data flowing efficiently from A to B.
The name comes from geometry: an arc is a portion of a curve—the most direct path between two points on a circle. In systems design, an Arc connects two services with the least complexity required to achieve the goal.
“The Arc pattern asks: what’s the shortest path between these two points that actually works in production?”
“The Arc pattern asks: what’s the shortest path between these two points that actually works in production?”
Principles
Data flows one way. Source to destination. No round-trips, no sync conflicts, no reconciliation logic. Simplicity through constraint.
Gmail → Notion (not Gmail ↔ Notion)
API → Database (not real-time bidirectional)
Event → Handler (fire and forget)
Transform only what’s necessary. Preserve source fidelity. Don’t normalize data that doesn’t need normalizing.
✓ Map fields directly when schemas align
✓ Preserve formatting (links, bold, structure)
✗ Don’t build complex ETL when simple mapping works
Arcs should be stateless. No servers to maintain. Run on-demand via scheduled triggers or webhooks. Pay only for what you use.
✓ Cloudflare Workers, AWS Lambda
✓ Cron triggers for polling patterns
✓ Webhook endpoints for push patterns
For multi-user systems, OAuth provides proper authorization. Each user authenticates with their own credentials. No shared secrets.
✓ User-scoped access tokens
✓ Automatic token refresh
✓ Revocable permissions
When to Use
• Data capture from one system to another
• Automated backups and archiving
• Event logging and analytics pipelines
• Notification forwarding
• Report generation from live data
• Real-time collaboration features
• Bidirectional sync requirements
• Complex data reconciliation
• Systems requiring strong consistency
• Interactive user workflows
Reference Implementation
Multi-user OAuth integration syncing labeled Gmail threads to a Notion database. 5-minute polling cycle, zero production failures, automatic contact creation.
Gmail API (OAuth) → Cloudflare Worker → Notion API
KV Store for token persistence and sync state
Cron trigger every 5 minutes
Related Patterns
When the Arc needs memory—understanding accumulates across syncs.
Arcs built on web standards (HTTP, OAuth, JSON) age well.