Stop Designing Agentic AI Systems Backwards: Start With Constraints, Then Choose the Architecture

There is a pattern I keep seeing when designing Agentic AI systems. We start by asking: Which LLM should we use? Should we use LangGraph? Where can MCP fit? Should we build multiple agents? Do we need RAG? Should we add memory? Should every step be handled by an autonomous agent? These are useful questions. But they are often asked too early . The result can be an architecture that is technically impressive but operationally difficult, expensive, slow, and surprisingly hard to trust. A better approach is to reverse the order: Start with the product outcome. Define the constraints. Then design the architecture. Choose the tools last. I have found a useful way to structure those constraints around four dimensions: LCFE L — Latency C — Cost F — Failure E — Evaluation This is not a framework that says every agentic system must look the same. It is a way of forcing architectural decisions to start with the realities of the product rather than the capabilities of the technology. In this article, I’ll walk through a concrete incident-automation example and show how starting with constraints can completely change the architecture. 1. The "backwards" way of designing an agent Imagine we want to build an AI Incident Resolution Assistant for an engineering organization. The goal sounds straightforward: When a production incident is raised, the AI should investigate the incident, gather context, identify the likely cause, recommend or perform remediation, and verify the result. Now imagine the team starts with the technology. The first architecture might look like this: User / Incident | v ┌──────────────┐ │ Triage Agent │ └──────┬───────┘ | v ┌────────────────┐ │ Research Agent │ └───────┬────────┘ | ┌──────────────┼──────────────┐ v v v Logs Agent Metrics Agent Knowledge Agent | | | └──────────────┼──────────────┘ | v ┌─────────────────┐ │ Remediation │ │ Agent │ └────────┬────────┘ | v ┌─────────────────┐ │ Validation Agent│ └────────┬────────┘ | v Resolution It looks sophis