Pattern
Arc
Efficient connection between points. One-directional sync with minimal transformation. The shortest path that works.
Definition
An Arc is 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?"
Principles
One Direction
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)
Minimal Transformation
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
Serverless Infrastructure
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
OAuth over API Keys
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
Good Fit
- • Data capture from one system to another
- • Automated backups and archiving
- • Event logging and analytics pipelines
- • Notification forwarding
- • Report generation from live data
Poor Fit
- • Real-time collaboration features
- • Bidirectional sync requirements
- • Complex data reconciliation
- • Systems requiring strong consistency
- • Interactive user workflows
Reference Implementation
Arc for Gmail
Gmail → Notion sync for Half Dozen
~11 hours to production
99.8% cost savings vs manual
Multi-user OAuth integration syncing labeled Gmail threads to a Notion database. 5-minute polling cycle, zero production failures, automatic contact creation.
Architecture
Gmail API (OAuth) → Cloudflare Worker → Notion API
KV Store for token persistence and sync state
Cron trigger every 5 minutes
Part of the CREATE SOMETHING Pattern Library