A written description of a product to give a development team overall guidance to the project architecture.

Structure:

1. Context and scope—rough overview of the landscape and what is being built.
2. Goals and non-goals—bulleted list of requirements.
3. Design—design overview and details.
4. Alternatives—alternative designs that would’ve achieved similar outcomes.
5. Cross-cutting concerns—how the design impacts security, privacy, observability.

Lifecycle:

1. Creation; rapid iteration—write the doc, share with the project team, drive to a first stable version.
2. Review—share and discuss with a wider range of colleagues.
3. Implementation; iteration—begin implementation.
4. Maintenance; learning—update the doc and re-read over time to find uncertainties.