Documenting architecture decisions
You should record decisions that affect the architecture of your service, in order to preserve the context of your choices.
As agile projects age, it is sometimes hard to keep track of the reasoning behind the decisions that were made. This is especially true as new people join the projects when those involved in the early stages are no longer around.
It is important to preserve that reasoning so that the current team can include it as context when making their own decisions about changes they need to make - for example, understanding whether a particular choice was made for the sake of expediency and can therefore be changed with little impact, or whether there were external reasons behind that decision that need to be factored in.
How to document decisions
Architecture decisions should be stored in version control so that there is a record of what was changed, who by, and when. Decisions that affect a specific application should be in that application’s code repository. You may also want to store larger-scale decisions in a central documentation repository.
A suggested format is the Architecture Decision Record, proposed by Michael Nygard in a blog post and since adopted widely. That post describes the format in full, but as a summary it consists of the following sections:
Title A description of the decision (not the problem)
Status eg Proposed, Accepted, Superseded
Context The facts behind the need to make the decision
Decision What the team has decided to do
Consequences Both positive and negative consequences of the decision