Build vs Buy

Is this core differentiation, can a provider solve it, what does integration cost, what does operating it cost, what happens when the provider fails.

The Build-vs-Buy Questions
▶ lab

Before "should we build payments ourselves?" can be answered, five questions have to be: is this our core differentiation, can a provider solve it, what does integrating cost, what does operating it cost, and what happens when the provider fails. The answers are the decision; the slogan is not.

Q · A capability the store needs — payments, email, search, image storage — could be built or bought. What do you ask before deciding, and why is "it would be faster to use a service" not yet an answer?
Core Differentiation

"Core" does not mean important; payment is essential and nobody chooses a store for it. Core means the reason a customer picks you — and that is the one thing you cannot buy, because a provider that solves it solves it for your competitors too.

Q · Everyone agrees the "core" of the system should be built in-house. How do you find out what the core actually is, and why is the answer so often not what the engineers think?
Integration and Operating Cost

"Build" is estimated for the week it takes; "buy" is estimated for the SDK call. Both are wrong the same way: the cost of a capability is what it takes to connect it and what it takes to live with it, and neither appears in the first estimate.

Q · Two options meet the requirement: build it, or integrate a provider. What are the costs that the obvious estimates leave out, and how do you find them before they find you?
When the Provider Fails

Every bought capability will fail, be slow, change under you, or rate-limit you — not as a possibility, as a schedule. The build-vs-buy decision owes the design a paragraph for each, and the payment provider and the email provider need very different paragraphs.

Q · You have decided to buy payment and email. What does the store do while each of them is down, slow, changed or throttled — and which of those four does the design actually have to survive?