Architecture Documentation

This guide covers architectural documentation practices, including architectural decision records (ADRs) and design documentation standards.

Architectural Decision Records

Architectural Decision Records (ADRs) document the significant architectural decisions made during the project lifecycle. They capture the context, reasoning, and consequences of decisions to provide future teams with the rationale behind architectural choices.

Purpose and Benefits

  • Historical context: Preserve the reasoning behind architectural decisions for future reference and team onboarding.

  • Decision accountability: Create a clear record of who made decisions and under what circumstances.

  • Alternative exploration: Document what was considered but not chosen, providing valuable context for future architectural reviews.

  • Change management: Track the evolution of architectural decisions over time through status updates and supersession.

ADR Format

Use the following format for all architectural decision records:

*******************************************************************************
[Number]. [Title]
*******************************************************************************

Status
===============================================================================

[Proposed | Accepted | Deprecated | Superseded by ADR-XXX]

Context
===============================================================================

[Describe the forces at play, constraints, and business/technical situation
that led to this decision. What problem are we trying to solve? What are the
key requirements and limitations?]

Decision
===============================================================================

[State the decision clearly and concisely. This should be the response to the
forces described in the Context section.]

Alternatives
===============================================================================

[Document what other options were considered and why each was rejected. This
provides valuable context for future decisions and shows that alternatives
were properly evaluated.]

Consequences
===============================================================================

[Describe the positive, negative, and neutral consequences of this decision.
Be honest about trade-offs and potential risks. Include impacts on:
- Performance
- Maintainability
- Team productivity
- System complexity
- Future flexibility]

ADR Lifecycle Management

Numbering Convention

  • Use sequential numbering: 001-initial-architecture.rst, 002-database-selection.rst, etc.

  • Zero-pad numbers to three digits for consistent sorting.

  • Use lowercase, hyphenated filenames.

Status Workflow

  • Proposed: Decision is under consideration and review.

  • Accepted: Decision has been approved and is being implemented.

  • Deprecated: Decision is no longer relevant but kept for historical context.

  • Superseded: Decision has been replaced by a newer ADR (reference the superseding ADR number).

Immutability Principle

  • Once an ADR is accepted, do not edit its content.

  • If circumstances change, create a new ADR that supersedes the previous one.

  • This preserves the historical decision context and reasoning.

Best Practices

Context Documentation

  • Focus on forces and constraints that drove the decision.

  • Include relevant business context, technical limitations, and team constraints.

  • Avoid implementation details - focus on the decision-making environment.

Clear Decision Statements

  • State decisions unambiguously.

  • Avoid hedging language like “might” or “could”.

  • Be specific about what will be done.

Comprehensive Alternatives

  • Document all seriously considered alternatives.

  • Explain why each alternative was rejected with specific reasons.

  • Include “do nothing” as an alternative when relevant.

Honest Consequences

  • Document both positive and negative consequences.

  • Include trade-offs and potential risks.

  • Consider long-term implications, not just immediate benefits.

Architecture Documentation Beyond ADRs

System Summary

The system summary (architecture/summary.rst) should provide a high-level overview of the system architecture including:

  • Major components: Key system modules, services, or subsystems.

  • Component relationships: How components interact and depend on each other.

  • Data flow: Major data paths through the system.

  • Deployment architecture: How components are distributed and deployed.

  • Key architectural patterns: Major patterns employed (MVC, microservices, event-driven, etc.).

Design Documents

Detailed design documents (under architecture/designs/) capture implementation-level specifications:

  • Interface specifications: API contracts, service interfaces, module APIs.

  • Data schemas: Database schemas, message formats, configuration structures.

  • Algorithm specifications: Detailed algorithmic approaches for complex processing.

  • Protocol definitions: Communication protocols between components.

Design Document Guidelines

  • Reference the architectural decisions that informed the design.

  • Include enough detail for implementation without over-specifying.

  • Use diagrams and examples to illustrate complex concepts.

  • Version design documents when significant changes occur.