system-planning-assistant

name	system-planning-assistant
description	High-level system architecture planning with component diagrams, scalability analysis, technology trade-offs, cost estimation, migration strategies, and technical specification documents

Purpose

Assist with strategic system design decisions, analyzing trade-offs, defining architectures, and creating technical specifications for complex systems.

When to Use

Use this skill when the task involves:

• Designing new system architecture from requirements
• Evaluating technology choices and trade-offs
• Planning system migrations or refactoring
• Creating technical specification documents
• Estimating infrastructure costs
• Analyzing scalability and reliability requirements

Constraints

• Follow Dependency Rule — dependencies point inward to domain
• Keep domain logic independent of frameworks and infrastructure
• Treat microservices as deployment strategy, not architecture
• Apply Domain-Driven Design for complex business domains
• Document explicit trade-offs for every major decision
• Include non-functional requirements (latency, throughput, availability)

Execution Steps

1. Gather requirements — Functional and non-functional (SLAs, scale targets)
2. Identify domains — Bounded contexts and their relationships
3. Design components — Services, databases, messaging, caching layers
4. Create diagrams — C4 model (context, container, component)
5. Analyze trade-offs — Document pros/cons of key decisions
6. Estimate resources — Team size, timeline, infrastructure costs
7. Define milestones — Phased delivery plan with risk mitigation

Examples

Input

Design architecture for a real-time bidding platform handling 100k requests/second

Output

# Real-Time Bidding Platform Architecture

## Requirements

- **Throughput**: 100,000 requests/second peak
- **Latency**: P99 < 50ms for bid decisions
- **Availability**: 99.95% SLA

## High-Level Architecture

```mermaid
graph TB
    subgraph Edge
        CDN[CloudFront CDN]
        LB[Application Load Balancer]
    end

    subgraph Compute
        BidService[Bid Service<br/>Auto-scaled EKS]
        AuctionEngine[Auction Engine<br/>In-memory processing]
    end

    subgraph Data
        Redis[(Redis Cluster<br/>Campaign cache)]
        Kafka[Kafka<br/>Event streaming]
        TimescaleDB[(TimescaleDB<br/>Analytics)]
    end

    CDN --> LB --> BidService
    BidService --> Redis
    BidService --> AuctionEngine
    AuctionEngine --> Kafka
    Kafka --> TimescaleDB
```

Key Decisions

Decision	Choice	Trade-off
Caching	Redis Cluster	+Low latency, -Eventual consistency
Database	TimescaleDB	+Time-series optimized, -Less ecosystem
Messaging	Kafka	+Durability, -Operational complexity

Cost Estimate (Monthly)

• EKS (50 nodes): ~$15,000
• Redis Cluster: ~$3,000
• Kafka (MSK): ~$2,500
• Data transfer: ~$5,000
• Total: ~$25,500/month

## Related Skills

- `terraform-aws-builder` — Implement infrastructure
- `database-schema-designer` — Design data models
- `kafka-stream-designer` — Event streaming design