Live case: you have thirty minutes to present a business case for migrating our monolith. Take us through the options, the sequence, the risks and how we would know it worked.
A monolith migration business case compares options in one unit finance can convert, shows the payback with stated assumptions, and names the number that would change the answer. Worked here, modularising in place pays back in about eighteen months; extracting services is a staged option decided on measured evidence.
Answer
Short answer
A monolith migration business case is a capital decision, so present it as one. Put the recommendation first. Compare doing nothing, modularising in place, extracting services and a full rewrite in one unit finance can convert, such as engineer-years. Show the payback from stated assumptions and name the number that would flip the answer. Then give a gated sequence and measures with baselines, including how much of the monolith gets retired.
In the worked case below, modularising in place pays back in about eighteen months. Extracting services pays back only if one uncertain figure turns out well, so it is funded as a second stage after a gate. The engineering mechanics behind the sequence are covered in replacing a system that cannot be switched off and choosing the cutover day. This page is the business case built on top of them.
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Likely follow-ups
- The CEO says the coordination-time figure comes from a survey and does not trust it. How do you get a number she will accept?
- Halfway through the extraction, the first domain shows no fall in coordination time. What do you present at the month-12 gate?
- Sales claims slow pricing changes cost them deals. How would you put that into the case without inventing a figure?
- How would the case change if the monolith also ran on hardware with an end-of-support date in eighteen months?
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