Architectural Decision Record ADR

Architecture Decision Record ADR is a compact and traceable documentation of all important decisions taken during the realization of a product. Use asciidoc or markdown and Git to have an agile and lean documentation of your major decisions.

The huge advantage of ADR is the timeline of the decisions. It tremendously help to understand the technical changes during the product lifecycle.

Definition

In each ADR file, write these sections:

• Title: short present tense imperative phrase, less than 50 characters, like a git commit message.
• Status: proposed, accepted, rejected, deprecated, superseded
• Context: what is the issue that we're seeing that is motivating this decision or change.
• Decision: what is the change that we're actually proposing or doing.
• Consequences: what becomes easier or more difficult to do because of this change.

I use asciidoc format to write all our architecture design records. You can add to the same git repository as the project, visualize differences and if desired generate a nice looking document. And my IDE IntelliJ IDEA has a nice plugin for this format.

Before using ADR I documented the decision changes as footnote in a word document. The ADR approach is way more legible and easier to trace with the help of git repositories.

Title 

These documents have names that are short noun phrases. For example, "ADR 1: Deployment on Ruby on Rails 3.0.10" or "ADR 9: LDAP for Multiple tenant Integration"

Context 

This section describes the forces at play, including technological, political, social, and project local. These forces are probably in tension, and should be called out as such. The language in this section is value-neutral. It is simply describing facts.

Decision 

This section describes our response to these forces. It is stated in full sentences, with active voice. "We will ..."

Status 

A decision may be "proposed" if the project stakeholders haven't agreed with it yet, or "accepted" once it is agreed. If a later ADR changes or reverses a decision, it may be marked as "deprecated" or "superseded" with a reference to its replacement(s). 

The status and the graph of related decisions can be tracked and visualize using tools. You can also track your decisions without any tools, a regular product has often less than hundred decisions. And you can always write a small parse utility to extract your dependency graph.

Consequences

This section describes the resulting context, after applying the decision. All consequences should be listed here, not just the "positive" ones. A particular decision may have positive, negative, and neutral consequences, but all of them affect the team and project in the future.

Tips and Tricks

The whole document describing an ADR should be one or two pages long. We will write each ADR as if it is a conversation with a future developer. This requires good writing style, with full sentences organized into paragraphs. Bullets are acceptable only for visual style, not as an excuse for writing sentence fragments (Bullets kill people, even PowerPoint bullets).

The approach is very similar to how you would document a software pattern.

Believe and respect is the prime directive. Regardless of what we discover, we must understand and truly believe that everyone does the best job he or she could, given what was known at the time, his or her skills and abilities, the resources available, and the situation at hand.