SaaS Platform Modernization
Legacy codebase slowing feature delivery. Modernized 200K LOC while shipping 12 features. Deploy time: 4 hours → 20 min.
The Problem
A B2B SaaS platform had accumulated significant technical debt. The frontend mixed patterns, the backend was a monolith with no clear boundaries, deployments were manual and error-prone, and new features took 3x longer than they should.
Constraints
Cannot pause feature development for migration
Team has varying experience levels across stack
Must maintain backwards compatibility with existing integrations
Budget constraints limited infrastructure changes
Technical Decisions
Frontend
- Established module boundaries using strangler fig pattern
- Built compatibility layer for old/new patterns to coexist
- Migrated from Redux to React Query for server state
- Introduced TypeScript incrementally with strict boundaries
Backend
- Decomposed monolith into logical service boundaries
- Created API versioning strategy for backwards compatibility
- Implemented database migrations without downtime
- Built new endpoints alongside legacy with feature flags
Infrastructure
- Containerized services for consistent environments
- Set up GitHub Actions CI/CD replacing manual deployments
- Implemented staging environment matching production
- Added automated rollback on deployment failures
Trade-offs Made
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Migration took longer than rewrite but maintained stability
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Kept suboptimal patterns in low-traffic areas to focus effort
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Accepted temporary code duplication during transition
Outcome
Migrated 60% of codebase over 8 months while shipping 12 features. Deployment time reduced from 4 hours to 20 minutes. Test coverage increased from 15% to 65%.
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