Context
Stage: Pre-seed → Seed
Team: 5 engineers (4 + me as CTO)
Mandate: Prepare system for post-seed scale without slowing feature development
Starting Architecture
- CDN + Firebase Auth
- Three auto-scaled services (AI, Next.js, Backend)
- Dual databases (Firebase + MongoDB)
- No execution guarantees between services
Problems Identified
Accidental Dual-Database Design
- Firebase + MongoDB evolved accidentally
- Increased consistency risk and debugging complexity
High API Latency from Over-Coordination
- Multiple synchronous hops per request
- Services blocking on each other
- AI and transactions tied to request lifecycles
No Execution Guarantees
- Requests could drop during autoscaling (2-3s windows)
- Service-to-service calls fragile under load
Poor Ownership Boundaries
- Backend organized by layers, not features
- External APIs scattered across codebase
Key Architectural Changes
1. Message Queues as Reliability Backbone
- Introduced message queue + dead-letter queues
- Service-to-service calls became asynchronous by default
- Long-running work moved off request paths
- APIs returned immediate "accepted/processing" responses
Impact: ~40-60% reduction in API response times, zero request loss
2. Redis for Coordination
- Sticky sessions and pub/sub
- Ensured cron jobs executed exactly once
- Reduced race conditions
3. Single Database Strategy
- Migrated fully to MongoDB cluster
- Removed dual-write failure modes
- Daily automated backups
4. Feature-Based Backend Modules
Restructured from vertical layers to horizontal features:
- Each feature: Router → Validator → Controller → Service → Repository
- All external integrations (Stripe, Discord, crypto) centralized
Impact: 30-40% reduction in debugging time, clear ownership
5. Full Observability
- Metrics, dashboards, infrastructure monitoring
- Faster root-cause analysis
- Earlier detection of regressions
Results
System Performance
- 40-60% lower response times for complex workflows
- Zero dropped requests during scaling
- Services scaled independently without bugs
Team Velocity
- 5-person team shipped: Messaging (new), Crypto flows (new), Continuous redesign
- Infrastructure changes didn't block features
- Clear module ownership improved parallelism
Key Lesson
This reflects the exact transition startups face after raising seed: early systems "work" but hide compounding risk. My role was to identify the architectural debt that actually matters and fix it without pausing growth.
8-month transformation during pre-seed → seed stage