For CIOs and IT leaders
Modernize your legacy system without switching it off
You can modernize legacy software incrementally by putting a stable interface in front of the old system, then replacing one part at a time behind it. The business keeps running on the old system until each new part has proved itself, so no single cutover weekend carries all the risk.
01 How we work
Why rewrites stall, and how a staged path avoids it
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Nobody knows what depends on what
An old system carries rules nobody wrote down. We map dependencies, data flows and overnight jobs before choosing what to move first, so surprises show up on paper instead of in production.
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One cutover carries all the risk
A full rewrite saves every risk for the last day. We release in increments behind a routing layer, so any part can be switched back to the old path if it misbehaves.
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Old and new drift apart
When both run side by side, their data can disagree. We plan the integration between them, compare outputs on real traffic and keep one system of record for each kind of data.
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The result has no owner
Modernization ends with your team running the new system. Documentation, tests and runbooks arrive with each stage, not in a handover at the very end.
What we'll tell you
If the old system is stable, affordable to run and not holding anything back, we will tell you to leave it alone for now.
Before and after
Watch the old system shrink, one step at a time
The strangler path in four pairs: how the old system works today, and what takes over each job once that part is replaced. The old system keeps running throughout, and nothing is switched off in one go.
Before
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One codebase for everything
Orders, billing, reporting and customer records share one deployment, so a small change needs a full release and a long test cycle.
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Overnight batch transfers
Integrations run as nightly file transfers, and other systems see yesterday's data until the next run finishes.
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Rules in a few heads
Business rules live in the code and in the memory of the people who wrote it, with little written down.
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Rare, risky releases
Releases happen a few times a year, out of hours, with a manual rollback plan that nobody wants to test.
After
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A routing layer in front
Requests pass through a stable interface, so traffic moves to a new service one route at a time, and back again if needed.
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Events and APIs
New parts publish changes as they happen, and the old system reads them through an adapter until it is retired.
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Rules captured as tests
Each rule a new service takes over is written as an automated test that runs against the old and new paths alike.
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Small, reversible releases
Each increment ships on its own with monitoring and a rollback, and the old path stays until the new one has proved itself.
How it starts
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Describe the system
You tell us what the system does, what it costs to keep and where it holds the business back. We ask about its users, its integrations and the constraints we must not break.
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Map before moving
A short assessment maps dependencies, data ownership and technical debt, and ends in a staged plan that names the first part to move and the reason for it.
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Move one part
We put the routing layer in place and modernize the first part behind it, with tests, monitoring and a rollback, while the old system carries on.
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Decide the next stage
You review the first stage against its acceptance criteria and choose to continue, change the order or pause. Each stage stands on its own.
The usual engagement model: Advisory and architecture
Ready to talk it through?
Start a conversation02 A typical situation
What this usually looks like
Picture a core system the business relies on every day. It runs on an old framework, releases are rare and tense, and a full rewrite was proposed once and then shelved.
We would map what depends on what, put a routing layer in front of the system and move the part that causes the most pain first. Old and new would run side by side, with their results compared on real traffic before the old path is retired.
03 Questions
Questions people ask
It depends on the size of the system and how many stages you choose to run. Each stage is planned and estimated on its own after the assessment, so you commit to one stage at a time rather than to a whole program up front.
Yes, and we recommend it. Your engineers know the history of the system; we bring the migration patterns, the testing and the release practice. Working side by side on each stage means your team can run and extend the result.
That is common. We start with characterization tests that record what the system does today, odd behavior included, so each new part is checked against them before it takes over any traffic.
It should notice fewer problems, not a cutover. Traffic moves to new parts gradually, with monitoring and a way back, and users only see a change when a stage is designed to give them one.
04 Start
Keep the business running while the system changes
Book a call with an engineer. We will ask what the system does, where it hurts and what must not break, and suggest where a staged path would start.
What happens next
- You pick a time, or send us a message.
- A person at Nexstella reads what you shared before we talk.
- You leave with a clear next step, even when that step is to wait.
Or write to [email protected]. Send a brief instead
Meet
Booking as .
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Send us two or three times that suit you. A person replies within one business day. The invite goes to the address above.
Prefer that we send you times?
What happens next
- You pick a time, or send us a message.
- A person at Nexstella reads what you shared before we talk.
- You leave with a clear next step, even when that step is to wait.
Contact
Send us a message
Pick the topic that fits and tell us what you are working on. A person replies within one business day.
Want the full picture? Read Legacy modernization.
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