8.3 KiB
Software Architecture Documentation (arc42)
About this document
Purpose. This document follows the arc42 template to describe, communicate, and evolve the architecture of the system in a clear, lightweight, and practical way. For background on arc42, see the official overview and documentation.
1. Introduction and Goals
Briefly explains why the system exists and which forces shape the architecture (business goals, functional scope, quality goals, stakeholders).
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1.1 Requirements Overview
Summarize key functional requirements or link to your product/backlog sources; keep this concise and focused on what drives architecture.
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1.2 Quality Goals
Capture 3–5 top quality attributes (e.g., performance, security, evolvability) that guide trade-offs and decisions.
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1.3 Stakeholders
List stakeholders (roles, responsibilities, concerns) whose needs the architecture must satisfy.
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2. Architecture Constraints
Record constraints (technical, organizational, legal, standards, runtime environments, toolchains) that restrict options and influence design.
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3. System Scope and Context
Defines what’s in/out of scope and how the system interacts with its environment (users, neighboring systems, external services).
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3.1 Business Context
Show business actors, interactions, and the value exchange; describe business-level inputs/outputs.
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3.2 Technical Context
Show technical interfaces, protocols, data formats, and integration endpoints between the system and external systems.
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4. Solution Strategy
Summarize the key architecture approach: principal patterns, frameworks, major decisions, and the rationale linked to goals and constraints.
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5. Building Block View
Explains the static decomposition of the system into building blocks (modules/components/subsystems), their responsibilities, and dependencies—the “floor plan”.
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5.1 Level 1 – System/Top-Level
Show the top-level breakdown into major subsystems or layers and how they collaborate.
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5.2 Level 2 – Key Components
Zoom into one or more subsystems from 5.1 and present their main components and relationships.
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5.3 Level 3 – Internal Structure (as needed)
Detail important components (data structures, classes, packages) when necessary for understanding or change.
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6. Runtime View
Describes significant scenarios to illustrate behavior and interactions of building blocks (sequence/flow, error paths, non-functional aspects).
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6.x Scenario
State context, triggers, participating blocks, message/interaction flow, and notable variations.
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7. Deployment View
Maps software artifacts to infrastructure (nodes, regions, runtime platforms), including redundancy, scaling, and operational concerns.
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7.1 Infrastructure Overview
Present environments (dev/test/stage/prod), regions/zones, and high-level topology.
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7.2 Deployment Mapping
Describe which artifacts run where; capture capacity, sizing assumptions, and elasticity.
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7.3 Cross-Environment Differences
List relevant differences (configs, data stores, integrations, security postures).
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8. Cross-Cutting Concepts
Central rules & approaches that apply across the system (domain model, architecture patterns, security, logging, error handling, configuration, i18n, etc.).
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8.1 Domain & Data
Share ubiquitous language, key domain concepts, data ownership, and data lifecycle.
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8.2 Security
Threat model highlights, authn/authz, secrets handling, crypto, secure defaults.
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8.3 Observability & Operations
Logging, metrics, tracing, health checks, dashboards, incident response hooks.
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8.4 Error Handling & Resilience
Policies for retries, timeouts, backoff, circuit breakers, idempotency.
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8.5 Configuration & Feature Flags
How configuration is structured, validated, and delivered; flag strategy.
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8.6 Performance & Caching
Hot paths, caching layers, data locality, performance budgets and profiles.
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8.7 Code & API Guidelines
Language/framework idioms, API style (REST/gRPC/GraphQL), versioning and compatibility rules.
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8.8 Compliance & Data Protection
Relevant standards/regulations (e.g., ISO, GDPR), data retention, audit trails.
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9. Architecture Decisions
A log of significant decisions (ADRs): context, options considered, decision, consequences, status (proposed/accepted/superseded).
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10. Quality Requirements
Elaborate quality scenarios (stimulus → response measure) tied to the goals in 1.2, including measurable acceptance criteria.
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10.1 Quality Tree
Visualize quality attributes and their refinements to orient priorities.
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10.2 Quality Scenarios
Concrete scenarios per attribute (e.g., “Under X load, 95th-pct latency ≤ Y ms”).
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11. Risks and Technical Debt
List key risks, assumptions, unknowns, and consciously accepted debt with mitigation/retirement plans.
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12. Glossary
Define important domain and technical terms to ensure a shared vocabulary; add abbreviations and acronyms.
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13. Best-Practice Requirements & Quality Checklist
Use these requirements to review and keep the document—and architecture—healthy over time.
13.1 Structural Completeness
- All 12 arc42 chapters present or explicitly marked “N/A” with rationale.
Add your content here… - Each section starts with a purpose blurb and ends with concrete, current content or a tracked TODO.
Add your content here… - Cross-references link related content (e.g., 4 ↔ 5/8, 1.2 ↔ 10).
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13.2 Consistency & Traceability
- Every major decision in 4 is backed by ADRs in 9 and aligned with 1.2/10.
Add your content here… - Interfaces in 3.2 are consistent with components in 5 and scenarios in 6.
Add your content here… - Deployment (7) matches runtime needs (6) and non-functional drivers (10).
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13.3 Quality & Measurability
- Quality goals (1.2) translated into measurable scenarios (10.2) with thresholds.
Add your content here… - Operational SLOs/SLIs defined and observable (8.3) and tied to alerts/dashboards.
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13.4 Risk & Debt Management
- Top risks ranked with mitigations, owners, and review cadence (11).
Add your content here… - Technical debt items carry impact, “pay-down” trigger, and target release.
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13.5 Security & Compliance Hygiene
- Threat model snapshot exists; controls mapped (8.2).
Add your content here… - Data protection & retention addressed; lawful bases documented (8.8).
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13.6 Evolution & Maintainability
- Document is versioned; changes tracked with changelog and ADR status updates.
Add your content here… - Architecture fitness checks (e.g., lightweight ATAM or quality scenario tests) scheduled.
Add your content here… - Diagrams are living (source-controlled), with legend, date, and level of detail.
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13.7 Fitness-for-Purpose Read-Through
- One-page executive summary aligns with goals and constraints.
Add your content here… - A new team member can understand system scope (3), big picture (5.1), and how to run it (7) within 60 minutes.
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