Architecture Decision

Systematically evaluate architecture decisions, document trade-offs, and select appropriate patterns for context. Provides frameworks for pattern selection, ADR creation, and technical debt management.

When to Use This Skill

Use this skill when:

• Making technology choices

• Evaluating architectural patterns

• Creating Architecture Decision Records

• Assessing technical debt

• Comparing design alternatives

Do NOT use this skill when:

• Writing implementation code

• Working on requirements (use requirements-analysis)

• Doing full system design (use system-design)

Core Principle

Context drives decisions. No pattern is universally good or bad. The best architecture is not the most elegant—it's the one that best serves its purpose while remaining maintainable and evolvable.

The Trade-off Triangle

Every architectural decision involves trade-offs:

Vertex

Maximized By

Cost

Simplicity

Monolith, sync communication, single DB

Scalability limits

Flexibility

Microservices, event-driven, plugins

Complexity overhead

Performance

Caching, denormalization, optimized code

Maintainability

Balance Strategies:

• Start simple, add complexity as needed

• Measure before optimizing

• Use abstractions to defer decisions

• Evolve incrementally

Quality Attributes

Performance

• Metrics: Response time (p50, p95, p99), throughput, resource utilization

• Tactics: Caching, load balancing, async processing

Scalability

• Dimensions: Horizontal, vertical, elastic

• Patterns: Stateless services, sharding, event streaming

Reliability

• Metrics: Uptime, MTBF, MTTR

• Patterns: Circuit breakers, retries, redundancy

Maintainability

• Factors: Readability, modularity, testability

• Patterns: Clean architecture, DDD, SOLID

Context-Pattern Mapping

Team Context

Context

Preferred Patterns

Avoid

Small team

Monolith, vertical slices, shared DB

Microservices, complex abstractions

Multiple teams

Service boundaries, API contracts

Shared state, tight coupling

Scale Context

Context

Preferred Patterns

Reasoning

Startup

Monolith first, vertical scaling

Optimize for development speed

Enterprise

Service mesh, horizontal scaling

Optimize for operational scale

Decision Matrix Template

Option

Consistency

Flexibility

Scalability

Complexity

Cost

Total

Option A

5

2

3

2

3

15

Option B

3

5

4

3

3

18

Option C

2

3

5

1

2

13

Weight factors based on context priorities.

Architecture Decision Record (ADR) Template

# ADR-[NUMBER]: [TITLE]

## Status

[Proposed | Accepted | Deprecated | Superseded]

## Context

[What is the situation requiring a decision?]

### Requirements

- [Requirement 1]

- [Requirement 2]

### Constraints

- [Constraint 1]

- [Constraint 2]

## Decision

[What is the decision?]

### Justification

- [Reason 1]

- [Reason 2]

## Consequences

### Positive

- [Benefit 1]

- [Benefit 2]

### Negative

- [Drawback 1]

- [Drawback 2]

## Alternatives Considered

### [Alternative 1]

Reason rejected: [Why]

### [Alternative 2]

Reason rejected: [Why]

Architectural Refactoring Patterns

Branch by Abstraction

• Create abstraction over current implementation

• Implement new solution behind abstraction

• Switch to new implementation

• Remove old implementation

Strangler Fig

• Identify boundary

• Implement new solution for new features

• Gradually migrate old features

• Retire old system

Parallel Run

• Implement new solution

• Run both old and new

• Compare results

• Switch when confident

Technical Debt Management

Debt Categories

Type

Examples

Payment Strategy

Design

Missing abstractions, tight coupling

Refactoring sprints

Code

Duplication, complexity, poor naming

Continuous cleanup

Test

Missing tests, flaky tests

Test improvement

Documentation

Missing docs, outdated diagrams

Documentation sprints

Metrics

• Debt ratio: Debt work / Total work (target < 20%)

• Interest rate: Extra effort due to debt

• Debt ceiling: Maximum acceptable debt

Anti-Patterns

Big Ball of Mud

Symptoms: No clear structure, everything depends on everything

Remedy: Identify boundaries, extract modules, establish interfaces

Distributed Monolith

Symptoms: Services must deploy together, sync chains, shared DBs

Remedy: Merge related services, async communication, separate DBs

Golden Hammer

Symptoms: One solution for all problems, force-fitting patterns

Remedy: Learn alternatives, evaluate objectively, prototype options

Related Skills

• system-design - Full system design with ADRs

• code-review - Implementation validation

• task-decomposition - Breaking down architectural work

• requirements-analysis - Understanding constraints