Direct Answer
MCP architecture consists of two principal layers: the Server Layer, which defines and hosts tools, and the Client Layer, which discovers tools and connects via the protocol. The relationship is complementary: the client discovers services through the protocol, while the server defines its tools in a standardized format. For scaling, MCP servers can be load-balanced, request tracing can be implemented, and tools can be sharded across regional maps.
Architectural Layers
1. Server Layer: defines tools (tool definition), processing, and security. Each tool is described via METADATA: name, description, input schema, output schema. 2. Client Layer: service discovery, connection, and execution. 3. Proxy Layer (optional): load balancing, caching, and protocol translation.
Scaling Patterns
??? Horizontal Scaling: multiple server copies behind a load balancer (Nginx/HAProxy). ??? Regional Sharding: tool distribution by geography to reduce latency. ??? Caching: cache repeated tool results in proxy layer to reduce calls. ??? State Sharding: keep tools stateless for easier scaling.
Examples from Our Directory
??? [microsoft/playwright-mcp](/en/mcp/microsoft-playwright-mcp): Architecture score 90/100 ??? clear server layer design + API docs. ??? [googleapis/genai-toolbox](/en/mcp/googleapis-genai-toolbox): Architecture score 95/100 ??? Google-trusted, includes spec compliance + Typed interfaces. ??? [cocoindex-io/cocoindex-code](/en/mcp/cocoindex-io-cocoindex-code): Architecture score 80/100 ??? needs improvement in state separation and adding caching layer.
Best Practices
??? Define every tool with full METADATA (name, description, input, output) ??? Use TLS everywhere for inter-layer communication ??? Apply stateless design for easier horizontal scaling ??? Monitor performance metrics (latency, error rate) per endpoint ??? Document API interfaces in OpenAPI format
FAQ
1. Can MCP be combined with other patterns? Yes, MCP can be combined with Event-Driven Architecture and CQRS as needed. 2. How to choose between single and multiple servers? Single server for small projects, multiple for production-scale projects. 3. Does MCP support communication between different models? Yes, via the unified protocol, different models can communicate through the same server. 4. What is the additional cost? The main cost is server resources and a load balancer, but the benefit is scalability and resilience.
Decision Summary
For developers designing MCP architecture: focus on stateless design + TLS + full tool METADATA. For current developers: assess your architecture via our decision engine for expandability improvements.