Why Architecture decision records (ADR) in Microservices? - Purpose & Use Cases

The Big Idea

What if your team could never forget why it made its most important design choices?

The Scenario

Imagine a team building a complex microservices system without writing down why they chose certain tools or designs. Months later, new team members join and ask, "Why did we pick this database?" or "What was the reason for this service split?" The original decisions are lost in chat logs and memory.

The Problem

Without clear records, teams waste time guessing past choices, repeat debates, and risk making conflicting changes. This slows development and causes errors because no one understands the original reasoning behind the architecture.

The Solution

Architecture decision records (ADRs) capture each important design choice in a simple, clear document. They explain the problem, options considered, the chosen solution, and why. This creates a shared history that everyone can refer to, keeping the team aligned and speeding up future decisions.

Before vs After

✗ Before

No documentation; rely on memory and scattered chats.

✓ After

# ADR Example
Title: Use PostgreSQL for user data
Status: Accepted
Context: Need reliable relational DB
Decision: Choose PostgreSQL for ACID compliance
Consequences: Easier joins, but requires setup

What It Enables

Teams can confidently evolve complex systems knowing the reasons behind every key architectural choice.

Real Life Example

A microservices team uses ADRs to track why they chose REST over gRPC for communication. Months later, when performance issues arise, they quickly revisit the ADR to evaluate if switching protocols makes sense.

Key Takeaways

ADRs document key architecture decisions clearly.

They prevent confusion and repeated debates.

They help teams maintain alignment over time.

Practice

1. What is the main purpose of an Architecture Decision Record (ADR) in microservices projects?

easy

A. To document important architecture decisions and their reasons

B. To write detailed code for each microservice

C. To track bugs and issues in the system

D. To monitor server performance metrics

Solution

1. Step 1: Understand the role of ADRs

   ADRs are used to record key architecture decisions and why they were made.

2. Step 2: Differentiate ADRs from other documents

   ADRs are not for code, bugs, or performance monitoring but for decision documentation.

3. Final Answer:

   To document important architecture decisions and their reasons -> Option A

4. Quick Check:

   Purpose of ADR = Document decisions [OK]

Hint: ADRs capture decisions, not code or bugs [OK]

Common Mistakes:

• Confusing ADRs with bug tracking
• Thinking ADRs are code documentation
• Assuming ADRs monitor system metrics

2. Which of the following is the correct basic structure of an ADR document?

easy

A. Title, Status, Context, Decision, Consequences

B. Title, Code, Tests, Deployment, Logs

C. Summary, Bugs, Fixes, Performance, Metrics

D. Introduction, User Stories, UI Design, API Endpoints

Solution

1. Step 1: Recall ADR standard sections

   ADRs typically include Title, Status, Context, Decision, and Consequences.

2. Step 2: Eliminate unrelated structures

   Options with code, bugs, or UI design are unrelated to ADR format.

3. Final Answer:

   Title, Status, Context, Decision, Consequences -> Option A

4. Quick Check:

   ADR structure = Title, Status, Context, Decision, Consequences [OK]

Hint: Look for Context and Consequences in ADR structure [OK]

Common Mistakes:

• Mixing ADR with test or deployment docs
• Confusing ADR with bug reports
• Including UI design in ADR

3. Given this ADR excerpt:

Title: Use REST for service communication
Status: Accepted
Context: Need simple, stateless communication
Decision: Use REST over HTTP
Consequences: Easier integration but higher latency

What is the main consequence documented here?

medium

A. REST requires stateful connections for speed

B. REST causes stateless communication to fail

C. REST reduces integration complexity and latency

D. REST leads to easier integration but higher latency

Solution

1. Step 1: Read the Consequences section carefully

   The consequence states "Easier integration but higher latency".

2. Step 2: Match the consequence with options

   REST leads to easier integration but higher latency matches exactly; others contradict the text.

3. Final Answer:

   REST leads to easier integration but higher latency -> Option D

4. Quick Check:

   Consequence = Easier integration, higher latency [OK]

Hint: Focus on Consequences section for effects [OK]

Common Mistakes:

• Ignoring the 'higher latency' part
• Assuming REST reduces latency
• Confusing stateless with stateful

4. You find an ADR with this status:

Status: Deprecated

What does this status indicate about the decision?

medium

A. The decision is newly proposed and under review

B. The decision is no longer recommended or used

C. The decision is currently active and enforced

D. The decision has been accepted but not implemented yet

Solution

1. Step 1: Understand ADR status meanings

   "Deprecated" means the decision is outdated and should not be used.

2. Step 2: Compare with other statuses

   New proposals are "Proposed", active ones "Accepted", so deprecated means no longer recommended.

3. Final Answer:

   The decision is no longer recommended or used -> Option B

4. Quick Check:

   Status 'Deprecated' = Not recommended [OK]

Hint: Deprecated means outdated, avoid using [OK]

Common Mistakes:

• Confusing deprecated with accepted
• Thinking deprecated means new proposal
• Assuming deprecated means pending

5. Your team must decide between using REST or gRPC for microservice communication. You want to document this choice clearly for future reference. Which is the best way to use an ADR in this situation?

hard

A. Write code samples for both REST and gRPC without explanation

B. Skip documentation and decide by majority vote only

C. Write an ADR with Context explaining needs, Decision stating REST or gRPC, and Consequences of each choice

D. Create a bug report to track this decision

Solution

1. Step 1: Identify ADR purpose for decision documentation

   ADRs should explain context, decision, and consequences clearly.

2. Step 2: Evaluate options for documenting architecture choices

   Only Write an ADR with Context explaining needs, Decision stating REST or gRPC, and Consequences of each choice uses ADR properly; others ignore documentation or misuse formats.

3. Final Answer:

   Write an ADR with Context explaining needs, Decision stating REST or gRPC, and Consequences of each choice -> Option C

4. Quick Check:

   Use ADR to document decision and consequences [OK]

Hint: Use ADR to record context, decision, and consequences [OK]

Common Mistakes:

• Skipping documentation
• Confusing ADR with bug reports
• Only writing code without explanation