Modernisering van legacy systemen & downtime-vrij replatformen

We use the strangler fig pattern with dual-write data replication running underneath it. The new Next.js frontend starts by consuming your legacy APIs while we migrate data to Supabase in the background via CDC streams. Traffic shifts progressively through CDN routing -- 5% canary first, then a controlled ramp to 100% over a few weeks. By the time we flip DNS, both systems are fully synchronized. The actual cutover takes minutes, not hours. And rollback is a single configuration change. That's it.

Honestly, 12-20 weeks covers most projects -- but that range moves depending on monolith complexity, database size, and how many downstream integrations you're carrying. We kick things off with a 2-week paid discovery phase that produces a complete migration graph and risk assessment, so there aren't surprises surfacing mid-project. The real reason timelines compress is that frontend and data migration workstreams run in parallel rather than sequentially. You're not sitting idle waiting for phase one to close before phase two can open.

Automated reconciliation runs every 15 minutes, comparing row counts, aggregate checksums, and referential integrity across both the legacy database and Supabase. We don't flip the write path until reconciliation has passed cleanly for 72 consecutive hours -- not approximately 72, not 70 with a good explanation. After cutover, the legacy database stays in read-only mode for 30 full days before decommission. It's there if we need it. We've never had to use it. But that safety net matters, and I'd never skip it.

Yes -- and nobody gets logged out, which is the thing people actually care about. We build a bridge layer that translates legacy session cookies to JWT tokens during the transition period. Supabase Auth handles JWT, OAuth2, SAML, and magic links natively. Credentials migrate with bcrypt-compatible hashing. The bridge typically runs 2-4 weeks -- long enough for all active sessions to expire naturally and re-authenticate against the new system. Users don't notice any of it. That's the goal.

Nothing here is binary. Every integration point is controlled by feature flags, so you're never in a position where rollback means a catastrophic all-or-nothing decision. Rolling back the Next.js frontend to the legacy system is a CDN routing change that takes effect in under 60 seconds. Database rollback routes writes back to the legacy system via the reverse-replication stream. But here's the thing -- we test the complete rollback procedure in staging before every production cutover. It's not something we figure out on the night. That would be insane.

Typically 40-50% reduction in hosting and maintenance costs within the first year. Legacy monoliths need vertical scaling -- bigger, increasingly expensive servers -- plus licensed databases like SQL Server or Oracle, plus dedicated ops teams whose entire job is just keeping the lights on. The Jamstack architecture flips that model entirely: edge-distributed static assets, serverless compute that scales to zero when idle, and Supabase's managed PostgreSQL at elastic pricing. We model the projected numbers during discovery, so you're working from real figures specific to your infrastructure -- not industry averages.

No -- and "rewrite everything simultaneously" isn't really a strategy anyway. The strangler fig pattern means business logic moves incrementally and deliberately. Critical paths go to Supabase Edge Functions or Next.js API routes first. Low-risk legacy logic can keep running behind the API compatibility layer for months while we work through higher priorities. We sequence based on actual performance impact and maintenance burden -- not some arbitrary checklist definition of what counts as finished.