November 2025
Intermediate to advanced
464 pages
11h 25m
English
Content preview from Domain-Driven Transformation
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Chapter 6. How to Approach the Transformation
What is the right course of action when approaching a legacy system? That is the topic of this chapter.
From a broad perspective, there are basically two options: either replace the legacy system completely or retain it by “merely” reshaping/refactoring it. Also, for replacement there are two variants: big bang replacement and step-by-step replacement.
On a more detailed level, different approaches can be used for different subsystems of a system.
We’ll stay at the broad level for the moment; the options are the following:
- Replacement
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- Big bang
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The new system is built from scratch on a greenfield site while the legacy system continues to operate. At some point in time, the switch is flipped from the legacy system to the new system.
- Step-by-step
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The new system is developed piece by piece and each piece is put into production when possible. At the same time, the corresponding functionality in the legacy system is shut down.
- Reshaping
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The big ball of mud is reformed with refactorings and remains in operation all the time.
Considering the advantages and disadvantages of the different types of transformation, you and other stakeholders will be in a good position to make the best decisions for your unique situation. To be sure, none of these options is easy or even simple to accomplish. There is, however, a greater or lesser degree of complexity from one to another.
Replacement—Big Bang
This first variant of replacement is shown in ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.