Architecting for concurrency in Elixir transcends simple process spawning; it requires a rigorous methodology to achieve 99.9999999% reliability (nine nines). This equates to roughly 1 second of outage every 30 years. To reach this standard, we use the Five-Question Framework.

The Structural Heuristic

Before writing a single line of OTP code, use these questions to decompose stateful problems into manageable primitives:

• Environment & Constraints: Is it a single node? A global cluster? What are the memory/IO limits?
• Focal Points: Where does the data live? Who "owns" the state (e.g., a results ledger)?
• Runtime Characteristics: How many concurrent requests? Are they CPU-bound or IO-bound?
• Protection: Which state must survive? What can we afford to lose and restart?
• Bootstrapping: How do we initialize the tree? Which services depend on others?

By treating these questions as constraints, you prevent the "Big Ball of Mud" concurrency where every process talks to every other process without clear hierarchies.