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Designing GenAI Systems: Complete Decision Framework

Core Questions

Foundation Decisions (Start Here):

  • Should I use RAG or direct prompting for my use case?
  • Should I enable memory on my agent? Short-term or long-term?
  • Should I fine-tune an LLM or just use prompt engineering?
  • What model should I choose for my use case?

Architecture Decisions (Next Level):

  • Should I have a single agent or decompose into multiple agents?
  • Should I use a vector database or traditional search?
  • Should I implement evaluation before or after deployment?
  • How should my agents communicate and collaborate?

Advanced Decisions (Complex Systems):

  • Should I use specialized vector databases or general-purpose ones?
  • Should I implement real-time or batch processing?
  • What runtime environment should I choose?
  • How should I handle agent communication and coordination?

When to Use This Guide

  • You understand GenAI fundamentals and need to make design decisions
  • You're building GenAI systems of any complexity
  • You need guidance on architectural trade-offs
  • You want to avoid common design mistakes
  • You're scaling from simple to complex systems

Agentic System Architecture Overview

Shape Legend

ShapeSymbolMeaningExamples
Diamond{{}}Decision/Control NodesAGENT, HUMAN, GUARDRAILS, OTHER AGENTS
Subroutine[[]]External Services/ProtocolsFOUNDATION MODEL, MCP Protocol, APIs, Knowledge Base
Cylinder[()]Data StorageMEMORY, DATABASES, VECTOR DATABASE
Hexagon{}Process/Action NodesTOOLS, EXTERNAL APIs
File[[]]Documents/FilesPROMPT, DOCUMENT STORE

Design Decision Framework

This framework provides the right level of detail for making GenAI system design decisions. Each decision point includes:

  • Clear alternatives with tabbed options for easy comparison
  • When to choose each option with specific criteria
  • Implementation guidance without overwhelming technical details
  • Trade-offs to help you make informed decisions
  • Decision factors that matter most for your use case

The framework focuses on architectural decisions rather than implementation details, giving you the information you need to make the right choices without getting lost in technical minutiae.

🎯 Critical Success Factors

Before diving into architectural decisions, understand that these three elements are the most important to get right in any agentic system:

1. Prompt Engineering & Design

  • Why it matters: Prompts are the interface between users and your AI system - they determine what the system understands and how it responds
  • What to focus on: Clear instructions, context setting, few-shot examples, output formatting, and edge case handling
  • Common mistakes: Vague prompts, missing context, poor examples, inconsistent formatting

2. Feedback Loops & Learning

  • Why it matters: Systems that can learn and improve from interactions become more valuable over time
  • What to focus on: User feedback collection, performance monitoring, automatic retraining, and continuous improvement
  • Common mistakes: No feedback mechanism, ignoring user signals, static systems that don't evolve

3. Success Metrics & Evaluation

  • Why it matters: Without proper measurement, you can't know if your system is working or how to improve it
  • What to focus on: Task completion rates, user satisfaction, response quality, system reliability, and business impact
  • Common mistakes: No metrics, wrong metrics, infrequent evaluation, ignoring qualitative feedback

4. Tools & Integrations

  • Why it matters: Tools are how your agents interact with the world - they determine what your system can actually do and how well it can do it
  • What to focus on: Tool selection, API reliability, error handling, data quality, and integration complexity
  • Common mistakes: Poor tool selection, unreliable APIs, no error handling, complex integrations, ignoring tool limitations

💡 Pro Tip: Spend 40% of your development time on these four areas. They have the highest impact on system success and user satisfaction.

Decision Priorities

Start with these decisions in order of importance:

🎯 Foundation Decisions (Must Get Right First)

These decisions have the highest impact on system success and are hardest to change later:

  1. Knowledge Integration - Determines your system's intelligence foundation
  2. Model Selection - Affects performance, cost, and capabilities
  3. Memory Strategy - Shapes user experience and system behavior
  4. Evaluation Strategy - Determines how you measure and improve success

🏗️ Architecture Decisions (Build on Foundation)

These decisions shape your system's structure and scalability:

  1. Single vs. Multi-Agent - Determines system complexity and capabilities
  2. Fine-tuning vs. Prompt Engineering - Affects development speed and performance
  3. Agent Communication - Critical for multi-agent coordination

Advanced Decisions (Optimize for Scale)

These decisions optimize performance and handle complexity:

  1. Vector Database Strategy - Affects search performance and cost
  2. Processing Strategy - Determines user experience and infrastructure needs
  3. Runtime Environment - Affects deployment, security, and operations

💡 Quick Start: If you're building your first system, focus on decisions 1-4. Add decisions 5-7 as you scale. Consider decisions 8-10 for production systems with high scale or complexity requirements.

Decisions You'll Need To Make

Deciding on Knowledge Infusion

Why this decision matters: Knowledge integration is the foundation of your GenAI system's intelligence. The approach you choose directly impacts accuracy, cost, complexity, and user experience. Getting this wrong can lead to hallucination, poor performance, or over-engineered solutions.

Key questions to ask yourself:

  1. What type of knowledge does my system need? (General vs. domain-specific, static vs. dynamic)
  2. How accurate do responses need to be? (Can tolerate some hallucination vs. need citations and sources)
  3. What's my infrastructure complexity tolerance? (Simple setup vs. can handle vector databases)
  4. How often does my knowledge change? (Static content vs. frequently updated information)
  5. What's my latency requirement? (Real-time responses vs. can tolerate retrieval delays)

Deciding on Memory Strategy

Why this decision matters: Memory strategy determines how your system handles context, personalization, and user experience continuity. The wrong choice can lead to frustrating user experiences, privacy violations, or unnecessary complexity.

Key questions to ask yourself:

  1. Do users expect the system to remember them? (Personalized experience vs. anonymous interactions)
  2. How important is conversation context? (Each query independent vs. building on previous interactions)
  3. What are my privacy requirements? (No data retention vs. user consent for memory)
  4. How complex should the user experience be? (Simple stateless vs. rich contextual interactions)
  5. What's my operational complexity tolerance? (Simple deployment vs. managing user data)

Deciding on Fine-tuning vs. Prompt Engineering

Why this decision matters: This choice determines your model's performance, development speed, and ongoing costs. The wrong approach can lead to poor accuracy, excessive costs, or unnecessary complexity that delays your time to market.

Key questions to ask yourself:

  1. How domain-specific are my requirements? (General tasks vs. specialized domain knowledge)
  2. What's my data situation? (Limited examples vs. large labeled datasets)
  3. What's my performance requirement? (Good enough vs. optimal accuracy)
  4. What's my time to market constraint? (Quick prototype vs. can invest in training)
  5. What's my budget for model customization? (Prompt engineering costs vs. fine-tuning infrastructure)

Deciding on Automated vs. Human Model Evaluation

Why this decision matters: Evaluation strategy determines how you measure success, catch issues, and ensure quality. The wrong approach can lead to undetected problems, slow feedback loops, or evaluation bottlenecks that slow down development.

Key questions to ask yourself:

  1. How do I define success for my system? (Objective metrics vs. subjective quality)
  2. What's my evaluation volume? (Few test cases vs. large-scale testing)
  3. How fast do I need feedback? (Real-time evaluation vs. can wait for human review)
  4. What's my quality tolerance? (Good enough vs. must be perfect)
  5. What's my evaluation budget? (Automated costs vs. human evaluation costs)

Deciding on Agent Runtime Environment

Why this decision matters: Your runtime environment determines scalability, security, compliance, and operational complexity. The wrong choice can lead to performance bottlenecks, security vulnerabilities, or compliance issues that are expensive to fix later.

Key questions to ask yourself:

  1. What are my compliance requirements? (Data residency, industry regulations, security standards)
  2. What's my scale requirement? (Small team vs. enterprise-scale deployment)
  3. What's my operational complexity tolerance? (Managed services vs. custom infrastructure)
  4. What's my budget for infrastructure? (Cloud costs vs. on-premises investment)
  5. What's my integration requirement? (Standalone vs. integrated with existing systems)

Deciding on Model Selection

Why this decision matters: Model selection directly impacts your system's performance, cost, and user experience. The wrong model can lead to poor accuracy, excessive costs, or performance bottlenecks that are difficult to fix later.

Key questions to ask yourself:

  1. What are my performance requirements? (Accuracy, latency, throughput needs)
  2. What's my budget for model inference? (Cost per token, monthly budget)
  3. How complex are my tasks? (Simple Q&A vs. complex reasoning and analysis)
  4. What's my scale requirement? (Low volume vs. high-throughput production)
  5. What are my compliance needs? (Data privacy, model transparency, audit requirements)

Deciding on Vector Database Strategy

Why this decision matters: Vector database choice directly impacts search performance, cost, and scalability. The wrong choice can lead to slow queries, expensive infrastructure, or scalability bottlenecks that are difficult to fix later.

Key questions to ask yourself:

  1. What's my scale requirement? (Small datasets vs. millions of vectors)
  2. What's my performance need? (Fast queries vs. cost optimization)
  3. What's my operational complexity tolerance? (Managed services vs. self-hosted)
  4. What's my budget for vector storage? (Pay-per-use vs. fixed costs)
  5. What are my integration requirements? (Simple setup vs. custom optimization)

Deciding on Real-time vs. Batch Processing

Why this decision matters: Processing strategy determines user experience, system complexity, and infrastructure costs. The wrong choice can lead to poor user experience, unnecessary complexity, or excessive costs.

Key questions to ask yourself:

  1. What's my user experience requirement? (Immediate responses vs. can wait for results)
  2. What's my data volume? (Small real-time vs. large batch processing)
  3. What's my cost tolerance? (Real-time infrastructure vs. batch efficiency)
  4. What's my complexity tolerance? (Simple batch vs. complex real-time systems)
  5. What are my latency requirements? (Sub-second vs. minutes/hours acceptable)

Deciding on Single Agent vs. Multi-Agent

Why this decision matters: Agent architecture fundamentally shapes your system's capabilities, complexity, and scalability. The wrong choice can lead to over-engineered solutions, performance bottlenecks, or limited functionality that doesn't meet user needs.

Key questions to ask yourself:

  1. How complex are the tasks I need to solve? (Simple single-purpose vs. complex multi-step workflows)
  2. Do I need specialized expertise? (General-purpose agent vs. domain-specific specialists)
  3. What's my scalability requirement? (Single user vs. multiple concurrent users with different needs)
  4. How important is fault tolerance? (Single point of failure vs. distributed resilience)
  5. What's my development complexity tolerance? (Simple single agent vs. complex coordination logic)

Deciding on Agent Communication and Collaboration

Note: This section only applies if you chose to implement a multi-agent system in the previous section. If you selected a single agent, you can skip this section.

Why this decision matters: Communication and collaboration patterns determine how your agents work together and with humans. The wrong approach can lead to coordination failures, inefficient workflows, or poor user experiences that undermine the value of your multi-agent system.

Key questions to ask yourself:

  1. How do my agents need to coordinate? (Independent tasks vs. complex workflows requiring coordination)
  2. What's my human involvement requirement? (Fully autonomous vs. human oversight and collaboration)
  3. How complex are my workflows? (Simple sequential tasks vs. complex multi-step processes)
  4. What's my failure tolerance? (Can handle agent failures vs. need robust coordination)
  5. What's my user experience goal? (Seamless automation vs. transparent human-AI collaboration)

Deciding on Tool Integration and Agent Capabilities

Why this decision matters: Tool integration determines what your agents can actually do in the real world. The wrong approach can lead to limited functionality, complex integrations, or security vulnerabilities that prevent your agents from delivering value.

Key questions to ask yourself:

  1. What external systems do my agents need to interact with? (APIs, databases, file systems, third-party services)
  2. How complex are my integration requirements? (Simple API calls vs. complex multi-step workflows)
  3. What's my security and compliance tolerance? (Basic authentication vs. enterprise-grade security)
  4. How important is standardization vs. customization? (Standard protocols vs. custom integrations)
  5. What's my team's expertise with different integration approaches? (MCP vs. custom connectors vs. API wrappers)

Common Pitfalls

Design Mistakes

  • Over-engineering: Starting with complex patterns when simple ones suffice
  • Under-evaluating: Not setting up proper testing and evaluation
  • Ignoring costs: Not considering API costs and infrastructure needs
  • Poor prompt design: Not investing time in prompt engineering

Technical Mistakes

  • No error handling: Not planning for API failures and timeouts
  • Poor data quality: Using low-quality training or context data
  • Security oversights: Not implementing proper input validation
  • Scalability issues: Not planning for increased load

Key Takeaways

  1. Start Simple: Begin with basic prompting before adding complexity
  2. Data is King: Good data makes good AI
  3. Standards Help: Use standards like MCP to make connections easier
  4. Feedback Loops Matter: Agentic control is about giving up control to the agent! Let it iterate but make sure it has a clear feedback loop!
  5. Test Everything: AI can be wrong, so always test and measure!

Next Steps

Ready to implement your GenAI system? Here's your action plan:

Immediate Actions

  • Evaluate your current architecture: Assess your existing system against the decision framework in this guide
  • Implement systematic evaluation: Set up automated model evaluation starting with basic metrics
  • Design a proof of concept: Create a simple system using the patterns outlined, focusing on clear responsibilities
  • Establish infrastructure practices: Implement IaC deployment patterns for your GenAI systems

Advanced Learning

🤖 AI Metadata (Click to expand)
# AI METADATA - DO NOT REMOVE OR MODIFY
# AI_UPDATE_INSTRUCTIONS:
# This document should be updated when new GenAI architectural patterns emerge,
# AWS services are updated, or industry best practices change significantly.
#
# 1. SCAN_SOURCES: Monitor AWS blogs, Anthropic engineering posts, Martin Fowler articles,
# and GitHub repositories for new architectural patterns and best practices
# 2. EXTRACT_DATA: Extract new patterns, decision factors, implementation strategies,
# and architectural trade-offs from authoritative sources
# 3. UPDATE_CONTENT: Add new patterns to appropriate sections, update decision factors,
# and ensure all examples remain current and relevant
# 4. VERIFY_CHANGES: Cross-reference new content with multiple sources and ensure
# consistency with existing patterns and decision frameworks
# 5. MAINTAIN_FORMAT: Preserve the structured format with clear pattern descriptions,
# decision factors, and implementation strategies
#
# CONTENT_MERGE_STATUS:
# - Simple and Complex Systems: Merged into single comprehensive decision framework
# - Decision Priority: Organized by importance and difficulty (Foundation → Architecture → Advanced)
# - Complete Coverage: All major GenAI system design decisions in one document
# - Quick Start Guidance: Clear progression from simple to complex decisions
#
# CONTENT_PATTERNS:
# - Pattern Name: Core Concept, Key Components, Architecture Benefits, Implementation Strategy, Decision Factors
# - Decision Framework: When to use, trade-offs, implementation considerations
# - Architecture Benefits: Scalability, maintainability, performance, cost considerations
# - Real-World Example: Comprehensive enterprise customer support system with PlantUML diagram
# - Decision Framework Principles: Right level of detail, clear alternatives, architectural focus
#
# BLOG_STRUCTURE_REQUIREMENTS:
# - Frontmatter: slug, title, description, authors, tags, date, draft status
# - Import Statements: Tabs, TabItem from @theme for interactive content
# - Core Questions: List of key questions the guide answers
# - When to Use: Clear guidance on when to use this specific guide
# - Tabbed Decision Framework: All major decisions in tabbed format for easy comparison
# - Implementation Guidance: Practical steps and considerations
# - Common Pitfalls: Mistakes to avoid with specific examples
# - Next Steps: Clear progression to related guides
# - Action Items: Specific, measurable next steps for readers
# - AI Metadata: Comprehensive metadata for future AI updates
#
# DATA_SOURCES:
# - AWS Blog Posts: /prompts/research/research-genai-arch-patterns.md (comprehensive research completed)
# - Anthropic Engineering: Claude Code best practices and agentic patterns
# - Industry Standards: Martin Fowler GenAI patterns and architectural principles
# - Additional Resources: MCP protocols, Nova Act, AgentCore, vector databases, LLM experimentation
#
# RESEARCH_STATUS:
# - Primary Sources: All AWS blog posts researched and documented
# - Additional Sources: All discovered resources researched and integrated
# - Real-World Example: Enterprise customer support system with full architecture
# - Components Section: Comprehensive GenAI components and their roles documented
# - Blog Post Structure: Adheres to /prompts/author/blog-post-structure.md
# - Decision Framework Consolidation: All "Deciding on..." sections moved to centralized Decision Framework
# - Autonomy Gradient Integration: Multi-agent pros enhanced with variable autonomy and risk management
# - Section Restructuring: Removed standalone patterns, integrated into decision tabs
# - Decision Framework Guidance: Added right level of detail guidance and decision framework principles
#
# CONTENT_SECTIONS:
# 1. Core Architectural Patterns (Direct Prompting, RAG, Agentic, Multi-Agent)
# 2. Vector Database and Storage Patterns (LanceDB, OpenSearch, caching strategies)
# 3. LLM Experimentation and MLOps Patterns (MLflow, SageMaker, evaluation frameworks)
# 4. Foundation Model Evaluation Patterns (automated evaluation, benchmarking)
# 5. End-to-End RAG Solution Patterns (Infrastructure as Code, knowledge bases)
# 6. Model Deployment and Serving Patterns (SageMaker JumpStart, CDK deployment)
# 7. Model Context Protocol (MCP) Patterns (universal integration, Bedrock agents)
# 8. GenAI Components and Their Roles (comprehensive component analysis)
# 9. Real-World Example: Enterprise Customer Support Agent System
#
# DECISION_FRAMEWORK_PRINCIPLES:
# - Right Level of Detail: Architectural decisions, not implementation minutiae
# - Clear Alternatives: Tabbed options for easy comparison
# - When to Choose: Specific criteria for each option
# - Implementation Guidance: Sufficient detail without overwhelming
# - Trade-offs: Informed decision-making factors
# - Decision Factors: Most important criteria for each use case
# - Architectural Focus: Strategic decisions over technical details
#
# WHY_TAB_GUIDANCE:
# - Default First Tab: Every tabbed decision section must start with a "Why" tab as default
# - Why This Decision Matters: Explain the importance and consequences of the decision
# - Key Questions Format: Provide 5 key questions users should ask themselves
# - Question Structure: "What/How/When/Where/Why" format with clear alternatives in parentheses
# - Decision Impact: Explain what happens if they get this decision wrong
# - Context Setting: Help users understand the stakes before diving into options
# - Examples of Why Content:
# - Knowledge Integration: "Foundation of system intelligence, impacts accuracy, cost, complexity"
# - Memory Strategy: "Determines context handling, personalization, user experience continuity"
# - Agent Architecture: "Shapes system capabilities, complexity, and scalability"
# - Model Strategy: "Determines performance, development speed, and ongoing costs"
# - Evaluation Strategy: "Determines success measurement, issue detection, quality assurance"
# - Runtime Environment: "Determines scalability, security, compliance, operational complexity"
#
# HOW_TAB_GUIDANCE:
# - Second Tab: Every tabbed decision section must have a "How" tab as the second tab
# - Due Diligence Checklist: Provide a structured checklist for making the decision
# - Checklist Format: 4 main categories with specific actionable items
# - Categories: Requirements Analysis, Constraints Evaluation, Testing/Validation, Production Planning
# - Actionable Items: Use checkbox format with specific, measurable tasks
# - Decision Process: Guide users through the systematic process of arriving at the right decision
# - Examples of How Content:
# - Knowledge Integration: "Assess knowledge requirements, evaluate constraints, test approach, plan production"
# - Memory Strategy: "Analyze UX requirements, evaluate constraints, design architecture, test validation"
# - Agent Architecture: "Analyze problem complexity, evaluate scalability needs, assess capabilities, design/test"
# - Model Strategy: "Assess domain requirements, evaluate constraints, test approaches, plan production"
# - Evaluation Strategy: "Define success metrics, assess capacity, design framework, implement/validate"
# - Runtime Environment: "Assess compliance needs, evaluate scale requirements, assess capabilities, plan deployment"
#
# REAL_WORLD_EXAMPLE:
# - Use Case: Enterprise customer support platform for 10,000+ concurrent users
# - Architecture: Complete PlantUML diagram with AWS sprites
# - Decision Factors: Foundation model selection, agent architecture, memory management
# - Scale Analysis: Performance metrics, bottlenecks, scaling opportunities
# - Cost Analysis: Monthly cost breakdown and optimization strategies
# - Security: Compliance features (GDPR, SOC 2, PCI DSS, HIPAA)
# - Monitoring: Comprehensive observability and alerting strategy
#
# UPDATE_TRIGGERS:
# - New AWS Bedrock features or services are released
# - Significant changes to Anthropic Claude capabilities or best practices
# - Major updates to industry-standard GenAI architectural patterns
# - New research papers or case studies on GenAI system architecture
# - Updates to MCP protocol or agent interoperability standards
#
# PLANTUML_DIAGRAM_MAINTENANCE:
# - AWS Icons: Use correct include paths from /prompts/author/plantuml-diagram.md
# - Version Control: Always use AWS Icons v20.0+ for latest compatibility
# - Include Syntax: Use !include AWSPuml/... not !includeurl for AWS icons
# - Common Fixes: SimpleStorageService.puml, SageMaker.puml, APIGateway.puml paths
# - Validation: Always check SVG content for "Cannot open URL" errors
# - Tab Structure: Diagram tab first (default), then PlantUML code tab
# - Static Files: Save corrected SVGs to /bytesofpurpose-blog/static/img/
# - Blog Integration: Use proper MDX syntax with <Tabs> and <TabItem> components
# - Iteration Process: Read SVG errors → Fix include paths → Regenerate → Validate
#
# FORMATTING_RULES:
# - Maintain consistent pattern structure: Core Concept → Key Components → Benefits → Implementation → Decision Factors
# - Use bullet points for lists and decision factors
# - Include specific examples and use cases for each pattern
# - Preserve the "I need to..." format in the Purpose section
# - Include PlantUML diagrams for complex architectures
# - Document real-world examples with comprehensive analysis
# - Use tabbed structure for PlantUML diagrams (diagram first, code second)
#
# MERMAID_DIAGRAM_GUIDANCE:
# - Use flowchart TB for architecture diagrams with proper shape semantics
# - Diamond {{}} for decision/control nodes (AGENT, HUMAN, GUARDRAILS, OTHER AGENTS)
# - Subroutine [[]] for external services/protocols (FOUNDATION MODEL, MCP, APIs, Knowledge Base)
# - Cylinder [()] for data storage (MEMORY, DATABASES, VECTOR DATABASE)
# - Hexagon {} for process/action nodes (TOOLS, EXTERNAL APIs)
# - File [[]] for documents/files (PROMPT, DOCUMENT STORE)
# - Include clickable links using click syntax: click A href "#section" "tooltip"
# - Add shape legend below diagram explaining each shape type and meaning
# - Use subgraphs to group related components logically
# - Show clear flow relationships between components
# - Include MCP servers in integration layer to show protocol implementation
# - Show human involvement and multi-agent coordination clearly
# - Make diagram interactive with links to relevant decision sections
#
# ARCHITECTURE_DIAGRAM_REQUIREMENTS:
# - High-level overview of agentic system components
# - Clear visual representation of relationships and flows
# - Interactive navigation to decision sections
# - Semantic shapes that match component functions
# - Logical grouping of related components
# - Show both single-agent and multi-agent scenarios
# - Include human involvement patterns
# - Demonstrate MCP integration architecture
# - Provide shape legend for clarity
# - Use professional, clean visual design
#
# UPDATE_FREQUENCY: Quarterly review, immediate updates for major AWS/Anthropic releases