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"We need to rewrite everything from scratch." – said every CTO ever.

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calendar_today • schedule1 min read

Sound familiar?

A legacy system is slow. Buggy. Nobody understands the code anymore.

The first instinct: Burn it down. Build it new.

But here's the problem with "rewrite from scratch":

It takes 2–3x longer than estimated
It costs a fortune (and then some)
It often fails (Google "rewrite from scratch disaster stories")
Your business doesn't stop while you rewrite

There's a better way.

Step-by-step modernization.
One module at a time.
No downtime.
Fixed price.
4–6 weeks.

My question to you:

Have you ever been part of a "big rewrite" project? How did it go? Success or disaster?

Let me know in the comments.

11 Comments

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Other solutions exist, such as the Adapter Pattern, etc., which are useful when upgrading legacy systems or Commercial Off-The-Shelf (COTS).

2 votes
•

@[Hussein Mahdi] Good point, The Adapter Pattern is perfect for gradual legacy migration – keep the old interface, replace modules behind it. I use a similar approach. Have you done this on larger projects?

1
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@[Jloosdev] I don't do that, but my colleagues do. Simply because no one has asked me to add a service to their old system . Now, at our company, we offer modern services on advanced systems built on the latest architectures.

I wish I had the chance to work on the old systems to see how they were built and to see the merits of these patterns.

0
•

I’m currently working on a heavily coupled .NET Framework 4.6 application that keeps growing while becoming more fragile with every release. In some parts, the codebase is so difficult to maintain that rewriting specific modules is actually faster and safer than continuing to patch bugs on top of bugs.

2 votes
•

@[Spyros] "Couldn't agree more. The rewrite fantasy dies fast – usually around month three.

What I keep seeing: teams go all in on a full rewrite, thinking it's the clean slate they need. Six months later, they're stuck with two broken systems instead of one.

There's a better way: modernize step by step. Keep the old system alive while rebuilding piece by piece. No all-or-nothing gamble. No burnt-out team.

After 4-6 weeks, you actually see results. Not just promises.

Legacy hurts. But a failed rewrite hurts more.

2
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@[Jloosdev] Couldn’t agree more… but unfortunately, when bosses already have something in place, even if it doesn’t work properly, they usually don’t want to change it.

1
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Every “rewrite from scratch” starts with optimism.

Then 6 months later:

  • old system still running
  • new system half finished
  • deadlines burning
  • team morale dead

Legacy code is painful.
But underestimating rewrites is a different kind of pain.

3 votes
•

@[buildbasekit] Exactly this. The excitement at the beginning – and then the crash.

I see it all the time: rewrites sound easy, but they're often the most expensive and riskiest path.

My approach: step-by-step modernization. Keep the old system running while replacing it piece by piece. No burnout, no chaos – real progress in 4-6 weeks.

Legacy is painful. A failed rewrite is worse.

2
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@[buildbasekit] The real benefit of rewriting comes when you truly understand:
what must change, what must stay, and why the old system evolved the way it did.

1
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@[Spyros] Exactly. A lot of legacy code looks “bad” until you realize half of it exists because of edge cases, business rules, or production incidents nobody documented.

The dangerous part of rewrites is accidentally deleting years of hidden knowledge along with the bad code.

1
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I’ve seen both sides. The successful rewrites happened when teams modernized incrementally instead of chasing a “perfect” v2. The disaster stories usually came from underestimating hidden business logic buried in the legacy system.

2 votes
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