Architecture decisions

A diagram has a short half-life. The reasoning behind it should have a long one, but it usually lives in one architect's head, and eighteen months later a team reopens a settled question because nobody can say why it was settled. Most of the architecture work I do is making a call, stating what it costs, and putting it somewhere it can be argued with.

What I do

• Target state with a road to it. A destination poster nobody can get to from here is worse than no target at all. The deliverable is the sequence: what moves first, what keeps running untouched, and which step is reversible if the first one is wrong.
• Decision records that name the cost. Context, the options considered, the choice, and the consequences, including the part that hurts. A decision that reads as free was not analysed. A decision whose price is written down survives the first time somebody pays it.
• C4 at the right altitude. A context diagram for the steering group, a container diagram for the teams, a component diagram only where the detail carries weight. Diagrams sized for their audience get used; one enormous diagram for everybody gets ignored by everybody.
• Build, buy, or exit. Vendor consolidation and decommissioning decisions come with a cost model: what the incumbent costs to keep, what the exit costs to run, and where the crossover is.
• Retiring a decision explicitly. Superseding an ADR, instead of letting it quietly stop being true, is what keeps the record worth reading two years in.

Evidenced by

• Deciding what crosses the SAP↔Snowflake seam: a decision record written in public. What crosses, what stays, and the rules that decide.
• Deciding where a Synapse estate goes: the same discipline one layer up, with an end date attached. Ten ordered rules across Fabric, Databricks and Snowflake, and a platform that priced best on the workloads it was not allowed to have.
• Cloud Gateway: one standard across two clouds, with the standing cost of that promise stated upfront.
• SAP S/4HANA Finance → Snowflake: a contract where SAP hands off to the lakehouse, and one region built as the reference architecture for the rest.
• Portfolio: sap-bdc-snowflake-blueprint turns the same handover question into nine ordered rules and a cost model you can run.

Background: TOGAF 9 Certified; Accenture Certified Technology Architect; C4, architecture decision records and DAMA-DMBOK governance vocabulary as daily practice.