Migrating a legacy system without stopping your business

The old system still works, but it's increasingly in the way#

Outdated software can "somehow work" for years - until it starts blocking growth: no support, security holes, no way to integrate, expensive changes, a single "expert on that system" without whom nothing moves. A migration gets you out of that trap - without stopping your business.

First decision: modernize or rewrite?#

You don't always need to start from scratch. We assess the system's state and recommend the cheapest sensible path:

• Refactoring / modernization - when the foundation is salvageable (tech upgrade, code cleanup, adding an API).
• Staged rewrite (strangler fig) - the new system grows alongside the old one and gradually takes over. Safest for a running business.
• Rewrite from scratch - when the old system is unmaintainable and the cost of patching outweighs the benefits.

How we migrate with no downtime#

1. Audit and dependency map - what the system does, who uses it, what it integrates with.
2. Stage plan - we split migration into small, reversible steps; after each, the business keeps running.
3. Data migration - the most underestimated step: cleaning, mapping, validation, trial migrations on a copy.
4. Parallel run - the new module runs alongside the old one until we confirm correctness.
5. Cutover and rollback - we switch traffic only when we have a fallback plan.

What we avoid (common risks)#

• "Big bang" migration - everything at once over a weekend. Highest risk; we use stages instead.
• Underestimated data migration - dirty data can sink a project. We run trial migrations early.
• No rollback plan - every stage has a fallback.

What it costs#

Cost depends on the system's state, data volume and number of integrations. We start with a short audit that yields a concrete plan and ranges - often modernization turns out cheaper than a rewrite. Billing: Fixed Scope (after the audit) or Time & Material (120 PLN/h net).

Why MDS Software#

We design migrations so your business keeps running the whole time, and after launch you get code ownership (end of single-vendor dependency) and SLA support. Full documentation and knowledge transfer included.

Let's start with an audit#

Describe your system (technology, age, integrations, pain points) and we'll come back with an assessment and a safe migration plan.

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