Old Systems Rebuilt to Last — Without the Big-Bang Rewrite
Legacy software doesn't have to be a liability. We audit, migrate, and progressively modernize aging systems — keeping your business running while we harden the foundation underneath it.
| The Problem | Typical Vendor | Hardened Soft |
|---|---|---|
| Undocumented system behaviour | Rewrites from scratch, losing business logic that took years to build | Audit and document all behaviour before a single line changes |
| Migration risk to production | Big-bang cutover with a downtime window and fingers crossed | Strangler fig pattern: new system runs alongside old, traffic shifted incrementally |
| Inherited technical debt | Patch over it and invoice for hours | Categorise debt by risk, fix high-risk items first, leave cosmetic debt for later |
| Vendor lock-in from old platform | Migrate to their preferred cloud and framework stack | Architecture-neutral — we pick what fits your team and runway |
| No test coverage on old code | Skip tests to hit the deadline | Characterisation tests written before modernisation; regression suite handed over |
| Business continuity during transition | Engineering teams go dark for months during migration | Existing features stay live; modernisation ships incrementally alongside BAU |
| Languages we migrate from | Delphi, VB6, Classic ASP, PHP 5.x, ColdFusion, COBOL, legacy Java, .NET Framework 2–4 |
| Target backend | Node.js (TypeScript), Go, Python, .NET 8, Java 21+ |
| Target frontend | React, Next.js, TypeScript, Tailwind CSS |
| Database migration targets | PostgreSQL, MySQL 8, MongoDB, Redis |
| Cloud platforms | AWS, Google Cloud, Azure, Hetzner (EU cost-optimised) |
| Containerisation | Docker, Kubernetes (EKS / GKE / AKS), Terraform |
| Auth modernisation | Auth0, Keycloak, AWS Cognito, custom OAuth2 / SAML |
| Observability | Datadog, Grafana + Prometheus, Sentry, OpenTelemetry |
We read the codebase, infrastructure, and documentation before touching anything. You get a written report: what's at risk, what's salvageable, and a phased modernisation plan with effort and cost estimates per phase. This is a paid engagement — you own the report regardless of what happens next.
Test coverage on critical paths, CI/CD pipeline, and observability introduced before migration begins. You can't modernise safely without the ability to see what's breaking. We build the safety net first.
Subsystems migrated in 2-week sprints. Strangler fig approach means new and old code run in parallel — traffic shifted after each sprint's acceptance tests pass. Business operations continue uninterrupted throughout.
Legacy system decommissioned once all traffic is confirmed stable on the new stack. Full documentation, runbooks, and knowledge transfer delivered. Your team can maintain it without us — that's the goal.
Almost always incremental. Full rewrites discard embedded business logic, take far longer than estimated, and carry the highest delivery risk. We only recommend a full rewrite when the existing codebase is structurally unrecoverable — and we document that assessment in writing before we suggest it.
We write characterisation tests against the existing system's actual behaviour before migration begins. This gives us a specification derived from reality, not from memory. Subject-matter experts on your side review and sign off on each domain before we migrate it.
No. The strangler fig approach means users interact with the old system until each migrated route passes acceptance testing. Traffic is shifted incrementally, with rollback available at every step. There is no downtime window — the cutover happens route by route, invisibly to users.
That's common. We begin by writing characterisation and integration tests against the running system — capturing what it actually does today. These become the regression suite that confirms the new system behaves identically.
The audit takes 1–2 weeks. Migration timelines depend heavily on system complexity and the scope of each phase — a single service can be modernised in 4–6 weeks; a full enterprise platform migration typically runs 3–12 months. We scope by phase so you control the budget incrementally.
Yes — and we prefer it. Knowledge transfer to your internal team is part of the engagement. We pair with your engineers, document architectural decisions, and hand over a system your team can maintain independently. We're not trying to create a dependency on us.
Start with a technical audit. We read the system, write up what we find, and give you an honest roadmap — no commitment required beyond the audit itself.
📩 contact@hardenedsoft.com