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Architecture Decision Records

Project: bifrost-extensions
Status: Active
Last Updated: 2026-04-05

Table of Contents

  1. Introduction
  2. ADR Index
  3. Status Legend
  4. Decision Drivers Summary
  5. ADR Categories
  6. How to Contribute
  7. ADR Templates
  8. Related Resources

Introduction

What are Architecture Decision Records?

An Architecture Decision Record (ADR) captures an important architectural decision made along with its context and consequences. ADRs help teams:

  • Document why decisions were made, not just what was decided
  • Preserve context for future team members
  • Enable informed reviews of past decisions
  • Track evolution of the system architecture
  • Support onboarding by providing historical context

ADR Process

┌─────────────┐    ┌─────────────┐    ┌─────────────┐    ┌─────────────┐
│   Proposed  │───▶│   Draft     │───▶│   Review    │───▶│   Accepted  │
│   (idea)    │    │   (writing) │    │   (feedback)│    │   (merged)  │
└─────────────┘    └─────────────┘    └─────────────┘    └──────┬──────┘
                                                                  │
                    ┌─────────────┐    ┌─────────────┐           │
                    │  Superseded │◄───│  Deprecated │◄──────────┘
                    │  (replaced) │    │  (obsolete) │
                    └─────────────┘    └─────────────┘

When to Write an ADR

Create an ADR when:

  • Choosing between competing technologies or approaches
  • Making structural changes to the codebase
  • Defining integration patterns with external systems
  • Establishing coding standards or conventions
  • Changing deployment or infrastructure strategies
  • Any decision with long-term architectural impact

ADR Lifecycle

Status Description Action Required
Proposed Idea identified, not yet written Assign author, create placeholder
Draft Being written, not ready for review Complete all sections
Under Review Open for team feedback Address comments, seek approval
Accepted Decision approved and merged Implement decision
Deprecated No longer recommended but still in use Plan migration
Superseded Replaced by a newer ADR Update with reference to replacement

ADR Index

Current ADRs

ID Title Status Date Author
ADR-001 Project Architecture Overview Accepted 2026-04-05 TBD
ADR-002 Technology Stack Selection Proposed 2026-04-05 TBD
ADR-003 Data Storage Strategy Proposed 2026-04-05 TBD
ADR-004 API Design Principles Proposed 2026-04-05 TBD
ADR-005 Authentication & Authorization Proposed 2026-04-05 TBD
ADR-006 Deployment Architecture Proposed 2026-04-05 TBD
ADR-007 Monitoring & Observability Proposed 2026-04-05 TBD
ADR-008 Security Architecture Proposed 2026-04-05 TBD
ADR-009 Performance Strategy Proposed 2026-04-05 TBD
ADR-010 Testing Approach Proposed 2026-04-05 TBD

Status Summary

Status Distribution:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
Accepted:     ████████░░░░░░░░░░░░  1 (10%)
Proposed:     ████████████████████  9 (90%)
Under Review: ░░░░░░░░░░░░░░░░░░░░  0 (0%)
Deprecated: ░░░░░░░░░░░░░░░░░░░░  0 (0%)
Superseded:   ░░░░░░░░░░░░░░░░░░░░  0 (0%)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
Total: 10

Status Legend

Accepted ✅

The decision has been reviewed and approved by the team. It represents the current state of the architecture and should be followed unless superseded.

Proposed 📝

The decision is being considered but not yet finalized. Comments and feedback are welcome.

Under Review 👀

The ADR is actively being discussed. Team members should provide feedback before the review period ends.

Deprecated ⚠️

The decision is no longer recommended but may still be in use. New implementations should avoid this approach.

Superseded 🔄

The decision has been replaced by a newer ADR. The superseded ADR contains a reference to its replacement.

Decision Drivers Summary

Common Decision Drivers Across ADRs

Driver Priority Description
Scalability High Ability to handle growth in users, data, or traffic
Maintainability High Ease of understanding, modifying, and extending
Security Critical Protection of data and system integrity
Performance High Response times, throughput, resource usage
Cost Medium Infrastructure and operational expenses
Time to Market Medium Speed of delivering features
Team Expertise Medium Alignment with team skills and knowledge
Ecosystem Medium Community support, tooling, third-party integrations
Vendor Lock-in Low Avoidance of proprietary dependencies
Compliance Critical Regulatory and policy requirements

Project-Specific Drivers

Driver Weight Rationale
Developer Experience High Productivity and code quality
Observability High Debugging and monitoring capabilities
Extensibility Medium Plugin and integration architecture
Reliability Critical Uptime and fault tolerance requirements

ADR Categories

By Domain

Category ADRs Description
Architecture ADR-001, ADR-006 System structure and deployment
Technology ADR-002 Language, framework, and tool choices
Data ADR-003 Storage, models, and persistence
API & Integration ADR-004, ADR-005 Interfaces and security
Operations ADR-007, ADR-008, ADR-009 Running and maintaining the system
Quality ADR-010 Testing and code quality

By Impact Level

Level Criteria Examples
Critical Affects entire system, hard to reverse Language choice, deployment platform
High Significant component impact Database migration, API versioning
Medium Localized impact Library replacement, coding standard
Low Minimal impact Utility library, dev tool

By Team

Team Responsibilities Related ADRs
Platform Infrastructure, deployment ADR-006, ADR-007
Backend APIs, data layer ADR-003, ADR-004, ADR-005
Frontend UI/UX, client-side ADR-002, ADR-010
Security Auth, compliance ADR-005, ADR-008
DevOps CI/CD, monitoring ADR-006, ADR-007, ADR-009

How to Contribute

Creating a New ADR

  1. Identify the Need

    • Is this a significant architectural decision?
    • Will others need to understand this choice in the future?
    • Does it impact multiple parts of the system?

  2. Reserve an ADR Number

    # Find the next available number
ls adr/ADR-*.md | sort -V | tail -1

  3. Use the Template

    • Copy the appropriate template from ADR Templates
    • Fill in all sections thoroughly

  4. Write with Context

    • Explain the problem clearly
    • Document alternatives considered
    • Capture the reasoning, not just the decision

  5. Submit for Review

    • Create a PR with the new ADR
    • Request review from stakeholders
    • Set status to "Under Review"

  6. Address Feedback

    • Incorporate suggestions
    • Update status based on consensus

  7. Merge and Announce

    • Once accepted, merge to main
    • Notify the team of the new decision

ADR Review Checklist

  • Problem statement is clear and complete
  • All relevant options are documented
  • Pros and cons are balanced and honest
  • Decision drivers are explicit
  • Consequences (positive and negative) are listed
  • Links to related ADRs or resources are included
  • Status is correctly set
  • Date and author are filled in

Updating Existing ADRs

When updating an ADR:

  • Add an "Amendments" section for minor updates
  • Create a new ADR if superseding (mark old as superseded)
  • Never delete or rewrite history - document the evolution

ADR File Naming

adr/ADR-NNN-Short-Descriptive-Title.md

Examples:
adr/ADR-001-Project-Architecture.md
adr/ADR-042-Microservice-Decomposition.md
adr/ADR-123-Migration-To-Rust.md

ADR Templates

Standard ADR Template

# ADR-NNN: [Title]

**Status:** Proposed | Under Review | Accepted | Deprecated | Superseded  
**Date:** YYYY-MM-DD  
**Author:** [Name]  
**Reviewers:** [Names]

---

## Context

### Problem Statement
[Clear description of the issue being addressed]

### Background
[Relevant history and current state]

### Constraints
[Limitations that affect the decision]

## Decision

### Selected Option
[The chosen approach]

### Rationale
[Why this option was selected]

## Consequences

### Positive
- [Benefit 1]
- [Benefit 2]

### Negative / Trade-offs
- [Drawback 1]
- [Drawback 2]

### Risks
- [Risk 1] → [Mitigation]

## Alternatives Considered

### Option 1: [Name]
- **Pros:** [List]
- **Cons:** [List]
- **Decision:** Rejected because [reason]

### Option 2: [Name]
- **Pros:** [List]
- **Cons:** [List]
- **Decision:** Rejected because [reason]

## Decision Drivers

| Driver | Weight | Impact |
|--------|--------|--------|
| [Driver] | High/Med/Low | Positive/Negative/Neutral |

## Implementation

### Migration Path
[Steps to implement this decision]

### Dependencies
- [ADR-XXX] - Related decision
- [External resource]

## Related Resources

- [Link to relevant documentation]
- [Link to proof of concept]
- [Link to related ADRs]

## Notes

[Additional context, discussions, or future considerations]

Lightweight ADR Template

For decisions with lower impact:

# ADR-NNN: [Title]

**Status:** Accepted  
**Date:** YYYY-MM-DD  
**Author:** [Name]

## Context
[One-paragraph problem statement]

## Decision
[The chosen approach with brief rationale]

## Consequences
- Good: [Benefits]
- Bad: [Trade-offs]

## Notes
[Links to relevant resources]

Technology Selection ADR Template

# ADR-NNN: [Technology] for [Use Case]

**Status:** [Status]  
**Date:** YYYY-MM-DD  
**Author:** [Name]

## Context

### Requirements
- [Functional requirement]
- [Non-functional requirement]

### Evaluation Criteria
| Criterion | Weight | Description |
|-----------|--------|-------------|
| Performance | High | Response time benchmarks |
| Maturity | Medium | Production readiness |
| Community | Medium | Support and ecosystem |

## Options Evaluated

| Option | Performance | Maturity | Community | Team Knowledge | Score |
|--------|-------------|----------|-----------|----------------|-------|
| [A] | 5 | 4 | 5 | 3 | 4.4 |
| [B] | 4 | 5 | 3 | 5 | 4.2 |
| [C] | 3 | 3 | 4 | 4 | 3.5 |

## Decision

Selected: **[Option A]**

Rationale: [Explanation based on criteria weights]

## Migration Plan

1. [Phase 1: Setup and experimentation]
2. [Phase 2: Pilot implementation]
3. [Phase 3: Full migration]
4. [Phase 4: Deprecation of old system]

## Consequences

[Positive and negative impacts]

Deprecation ADR Template

# ADR-NNN: Deprecate [Feature/Technology]

**Status:** Deprecated  
**Date:** YYYY-MM-DD  
**Supersedes:** ADR-XXX  
**Author:** [Name]

## Context
[Why the original decision is no longer optimal]

## Deprecation Rationale
[Explanation of why this is being deprecated]

## Replacement
[What should be used instead - link to new ADR]

## Migration Timeline

| Phase | Date | Action |
|-------|------|--------|
| Announcement | YYYY-MM-DD | Notify stakeholders |
| Deprecation | YYYY-MM-DD | Mark as deprecated |
| Migration | YYYY-MM-DD | Teams migrate to replacement |
| Removal | YYYY-MM-DD | Complete removal |

## Affected Systems
- [System 1]
- [System 2]

## Notes
[Additional context about the deprecation]

Related Resources

Internal Documentation

Resource Location Description
Architecture Overview ./ARCHITECTURE.md High-level system architecture
API Documentation ./docs/api API reference and guides
Development Guide ./CONTRIBUTING.md Contribution guidelines
Security Policy ./SECURITY.md Security practices

External Resources

Resource URL Description
ADR GitHub Organization https://adr.github.io/ ADR methodology and tools
Markdown ADR Spec https://adr.github.io/madr/ Markdown ADR format
Architecture Patterns https://martinfowler.com/architecture/ Patterns and practices

Tools

Tool Purpose Link
adr-tools CLI for managing ADRs https://github.com/npryce/adr-tools
log4brains Web-based ADR viewer https://github.com/thomvaill/log4brains
madr Markdown ADR template https://adr.github.io/madr/

Glossary

Term Definition
ADR Architecture Decision Record
RFC Request for Comments (similar to ADR but broader scope)
Status Current state of the ADR in its lifecycle
Driver Factor that influences the architectural decision
Consequence Result or impact of the decision
Superseded Replaced by a newer ADR
Deprecated No longer recommended but may still exist

Change Log

Date Change Author
2026-04-05 Initial ADR index created Automated
2026-04-05 ADR-001 accepted TBD

This document is a living index. As ADRs are added, updated, or superseded, this index should be maintained to reflect the current state of architectural decisions.

Questions? Contact the architecture team or open an issue for discussion.