Elevate Your Engineering Culture: The Power of Documenting Architecture Decisions
Learn why clear, accessible decision logs can enable collaboration and learning.
Imagine this scenario: Your team’s been heads-down for months on a new initiative - refactoring an aging monolith into microservices. The architecture discussions were epic. You debated everything from data persistence strategies to synchronous vs. asynchronous communication. Yet six months down the line, a new team member asks, “Why are we using Kafka again?” Everyone shrugs. The conversation is hazy in everyone’s memory, and hours are lost retracing those original decisions. Sounds familiar?
This is exactly where Architecture Decision Records (ADRs) come in. They capture and preserve the context, rationale, and trade-offs for the most critical decisions you make, ensuring knowledge isn’t lost and that your team can move forward confidently. By writing architecture decisions down, you create a durable knowledge asset that will outlive the project itself.
In this article, we’ll explore how documenting architecture decisions can transform your engineering organization from one that’s plagued by constant rehashing of old debates to one that runs like a well-oiled, knowledge-sharing machine.
What is Architecture Decision Record?
An Architecture Decision Record (ADR) is a concise document that captures an important design choice and the context around it. Think of it as a single-page summary of a pivotal decision: the motivation, the alternatives considered, the trade-offs, and the consequences. Each ADR is typically stored in a repository, creating a living log of how and why your architecture evolved.
Instead of relying on memory or long-forgotten meeting notes, you can pull up an ADR to see exactly what led your team to adopt technology X or design pattern Y.
Why Documenting Architecture Decisions Matters
1. A Single Source of Truth
Think of ADRs as a time capsule for your architecture’s evolution. They provide a single source of truth that any current - or future - team member can consult. No more searching through Slack threads or email chains to figure out why something was done a certain way.
2. Better Onboarding and Cross-Team Collaboration
ADRs remove guesswork for new hires or teams that need to integrate with your system. When decisions are explicitly documented, teams can quickly grasp design intentions, constraints, and trade-offs. This accelerates onboarding and prevents siloed knowledge.
3. Encourage Thoughtful, Data-Driven Decisions
Writing an ADR forces you to articulate your thought process. You must consider alternatives, articulate the rationale, and understand the implications. This type of deliberate, data-driven approach elevates the quality of architectural discussions.
4. Simplify Architecture Evolution
Architectures evolve and that’s normal. When you deprecate, change, or supersede a decision, referencing and updating the original ADR clarifies the historical context. It’s a lightweight but powerful way to manage the living, breathing entity that is your system architecture.
A Simple ADR Template
Below is a straightforward example (based on this template) you can start using today. Keep it simple. The goal is to document the most important aspects of each architectural decision - no need to write anything elaborate and long as this could discourage from writing ADRs in the long run.
## Title
<Short title describing what this ADR is about>
## Status
<Accepted | Superseded by ADR-xx>
## Date
<Date>
## Context
<Describe the nature of the problem that requires a decision and all relevant context around it.>
## Decision
<Describe briefly the decision that was made.>
## Rationale
<Explain the reasoning behind the decision and its trade-offs and why it is consider the preferred option.>
## Implications
<Describe the side-effects of this decision, both technical and not-technical one. Include both positive and negative implications>
## Alternatives Considered
<Describe any alternative solutions that were considered as a potential solution and why they were not chosen.>
## References
<Optional. Include any links to resources that influenced the decision or might be helpful in understanding the subject of the decision in depth>Example: Migrating from Synchronous HTTP API to Kafka
Here’s a fictional - but very plausible - example you might see in an Architecture Decision Repository.
## Title
Migrating from Synchronous HTTP API to Kafka
## Status
Accepted
## Date
2025-03-10
## Context
Our microservices currently communicate via synchronous HTTP APIs, causing latency issues and occasional disruptions when one service is unavailable. Also, the cost to handle the entire traffic is very high. Most of the communication, especially reads, don't require synchronous flow. We also anticipate a need to handle significantly higher request volumes in the near future. To increase resiliency, scalability and cost-efficiency, an asynchronous communication would be preferred.
## Decision
We will transition from synchronous HTTP API calls to a Kafka-based event-driven architecture for communication between our microservices.
## Rationale
- Scalability: Kafka’s event-driven model allows simple horizontal scaling of consumers, which is critical for our anticipated traffic growth and is also very cost-efficient.
- Resilience: Asynchronous messaging decouples microservices, so one service’s downtime doesn’t cascade throughout the system, which is especially important for writes/commands. That will allow us to take advantage of Saga pattern.
- Cost-efficiency: A simple proof of concept indicates that just 3 Kafka consumers can read the equivalent amount of data as 25 Sidekiq workers reading from HTTP API. Also, it implies that we will be able to scale down web workers of the upstream service by 40% as we won't be reading this data from the HTP API.
## Implications
- Operational Overhead: We need to maintain a Kafka cluster, which introduces new complexity for monitoring, alerting, and administration. Amazon MSK service can be a great solution here.
- Kafka Learning Curve: Engineers will need to gain familiarity with event-driven design patterns and Kafka itself.
- Deployment and Migration Plan: We’ll roll out event streams incrementally to avoid a “big bang” migration. Secondary microservices will be adapted first, followed by the more critical ones.
## Alternatives Considered
1. Continue with Synchronous HTTP: Would be simpler to maintain, but scalability, resiliency and cost-efficiency trade-offs are not acceptable in the long run.
2. Use a Different Message Broker (e.g.RabbitMQ): While viable, Kafka’s persistence and proven track record with large-scale event processing made it more appealing.
## References
- [Kafka Documentation](https://kafka.apache.org/documentation/)
- [Event-Driven Architecture Patterns](https://www.confluent.io/learn/event-driven-architecture/)When to Write (and When Not to Write) an ADR
ADRs are meant to capture key decisions that have long-term implications for your system or organization. If a decision introduces a new dependency, alters fundamental data flows, or significantly affects architecture and team processes, it likely requires an ADR.
On the other hand, minor decisions - like tweaking a library version or refactoring a single function usually don’t need an official record.
Use your judgment: if it’s significant enough that others might question later or that will be difficult to undo, document it. Otherwise, don’t let the process become an administrative burden.
Recommendations for Organizing ADRs
Once you start adopting ADRs, having a clear organizational strategy is essential. Many teams keep their ADRs in a dedicated folder within their source control (like docs/adrs), ensuring everything is versioned alongside the code.
For those who prefer a more dynamic knowledge base, solutions like Notion can be excellent for storing and collaborating on ADRs. You can create a Notion database, tag each ADR with relevant topics (e.g., “Security,” “Scalability,” “Data Layer”), and link out to related discussions or artifacts.
The key is to pick a system that fits your team’s workflow - something both discoverable and easy to maintain. By keeping ADRs well-organized and centrally accessible, you amplify their impact and make it far more likely your team will actually reference and update them over time.
Wrapping up
ADRs are not meant to add bureaucratic overhead. Rather, they serve as lightweight documentation that captures the heart of each major technical decision - protecting your team from knowledge loss, rehashing old arguments, and misalignments. By inroducing ADRs into your engineering culture, you will enable stronger collaboration, make more informed decisions, and onboard new team members with ease.
The next time your architecture evolves, don’t leave your decisions to chance or memory. Make them transparent, searchable, and future-proof by documenting them in an Architecture Decision Record. You’ll thank yourself the next time someone inevitably asks, “Wait, why did we choose this again?”