Practice the design decision
Use this two-page workbook to separate independent notifications from coordinated workflows. Answer six original scenarios before reading the worked solutions.
- Identify who owns the business invariant.
- State ordering, subscription lifetime and failure behavior.
- Explain how duplicate delivery is handled.
- Prefer a direct call when indirection adds no value.
What you will learn
Observer supports independent subscribers; a mediator-style coordinator makes collaboration rules explicit. Neither name guarantees durable delivery, transactions or successful retries. The workbook includes practical checks for unsubscribe behavior and duplicate-safe effects.
The .NET interface and lifecycle discussion is grounded in Microsoft Learn: Observer design pattern and Observer best practices. The exercises and architectural trade-offs are original.
No code execution is required for these design-reasoning exercises.