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Migration Lead

Migrating a Legacy PHP Monolith to .NET

A phased strangler-fig migration that modernized a critical app with zero unplanned downtime.

ASP.NET CoreEF CoreAzure App ServiceGitHub Actions

Problem

A brittle PHP monolith blocked new features and was expensive to operate.

Outcome

Fully migrated to ASP.NET Core over two quarters with no unplanned downtime.

0 min

Unplanned downtime

hours

Deploy lead time

-70%

Error rate

Context

The business depended on a PHP monolith that had grown organically for years. Every change was risky, and the deployment process was manual and slow.

Strategy

I applied the strangler-fig pattern: stand up a new .NET application in front of the legacy system and migrate one capability at a time, routing traffic incrementally.

Client ─▶ Reverse proxy
           ├─▶ /orders  ─▶ .NET (migrated)
           └─▶ /*       ─▶ legacy PHP (shrinking)

Execution

  • Introduced an anti-corruption layer to translate between old and new models.
  • Backfilled data with idempotent, resumable jobs.
  • Added CI/CD with GitHub Actions to make deploys boring and frequent.

Each migrated route shipped behind a feature flag, so rollback was a config change rather than a redeploy.

Results

The migration completed over two quarters with zero unplanned downtime, a 70% drop in error rate, and deploy lead times measured in hours instead of days.

Lessons Learned

Incremental migration beats a big-bang rewrite: value ships continuously, and risk stays small and reversible at every step.