Legacy system modernization: stage by stage, with no downtime for your operations
Legacy system modernization in pieces while the old system keeps running. First we put a new API layer next to it, then move module by module, and switch the old part off only once the new one is proven.
What hurts
Legacy system modernization gets postponed for years because the old system runs the whole business. The people who wrote it left long ago. There is no documentation, and every change breaks something unexpected.
New needs do not fit the old architecture. Connecting a bank, a marketplace or an AI agent is impossible because there is no API. Staff copy data between the old system and new tools by hand.
A full rewrite is scary and expensive. Big bang weekend migrations end in downtime and lost data. You cannot afford to stop operations.
What we build
- Audit of the current system: code, database, integrations, who uses it and how
- Documentation of what exists and a dependency map between modules
- A migration plan using the strangler pattern: module order, risks, rollback points
- A new API layer on top of the old system so integrations work now
- Moving modules to NestJS and PostgreSQL with old and new running side by side
- Data migration and reconciliation with automated checks
- AI on top of old data: search, reports, document processing
- Automated tests, CI/CD and monitoring for every migrated module
What you get
- A modern system in production and the old modules switched off
- Documentation of the architecture, data and integrations
- APIs for connecting new services
- Data reconciliation reports after every stage
- Source code with IP assigned to you by contract
How we measure the result
- Number of incidents and downtime during migration
- Share of functions moved off the old system
- Time to ship a typical change
- Number of data mismatches found in reconciliation
Systems and stack
Industries
Questions
How much does legacy modernization cost?
From $15,000 for the first stage. The price depends on the size and state of the system, the number of integrations, data volume and how strict the uptime requirements are. After the audit you get a fixed estimate per stage. Overruns through our fault are on us.
Will there be downtime?
We plan for none. Old and new run in parallel, and traffic moves over gradually, starting with part of the users. Every step has a rollback plan. Any short maintenance windows are agreed with you in advance.
How long does modernization take?
The first stage is usually 10-20 weeks. Replacing a large system fully takes longer and runs in stages, each with its own estimate. You get a useful result, such as an integration API, in the first stage already.
What if the documentation and original developers are gone?
That is the usual case. We rebuild the logic from the code, the database and interviews with users. The result becomes documentation you keep whatever happens next.
Where does AI fit in?
In two ways. AI helps us read and document old code faster. For you, AI adds search and reporting over data that used to be locked away. AI sometimes gets things wrong, so every migration step is confirmed by tests and data reconciliation.
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