I fell asleep only part way thru.
The answer isn't that hard.
Software architecture is the process/skill of breaking down problems/solutions into systems and subsystems that are appropriately modular, encapsulated with well defined interfaces.
It's not quite that simple, you need to decide on centralise, distributed etc especially in regard to your known scalability requirements, but these might end up being different than you foresee.
The rest is execution.
