How Microsoft’s Release Flow Revamped DevOps Efficiency

DevOps at Microsoft

This series explores Microsoft’s DevOps transformation, drawing on first‑hand Azure DevOps material to present an objective, comprehensive view of the practices involved.

Microsoft's branch strategy: Release Flow

Agile principles and practices

DevSecOps cultural shift

Live‑Site production‑first model

Transition from monolithic apps to cloud services

Feature‑flag experimentation

Test left‑shift for speed and reliability

Test right‑shift for production validation

Secure deployment practices

Elastic engineering in the cloud

Microsoft's Branch Strategy

Before the transformation

Microsoft originally used a heavyweight branching model: a shared trunk, group branches for large product teams, subgroup branches for smaller teams, and feature branches for individual work. Each level required synchronization and merging back up the hierarchy, leading to "merge hell" and low efficiency when many developers were involved.

Transformation idea

With the rise of Git, Microsoft moved to a single‑trunk workflow using Pull Requests, which helps avoid technical debt and ensures stable releases. The Azure DevOps team gradually adopted a model called "Release Flow" that supports large‑scale, trunk‑based development across multiple offices and hundreds of engineers.

Development process

1. Branch

When a developer wants to implement a feature or fix a bug, they create a short‑lived feature branch from the main integration branch

master

. Early commits and feature flags keep branches lightweight.

2. Push

Developers push the local branch to the remote server and open a Pull Request. Branch names follow a convention such as

users/username/feature

, where

username

is the developer’s account.

3. Pull Request

The Pull Request merges the feature branch back into

master

. It triggers a build and runs about 60,000 L0/L1 tests within five minutes, followed by code review to catch issues not found by automated tests.

4. Merge

After all build rules pass and the review is approved, the Pull Request merges into

master

. Additional, longer‑running acceptance tests are then executed to balance rapid feedback with thorough verification.

Release Hotfix

For urgent fixes, developers start from

master

, make changes, complete a Pull Request, and merge back to

master

. This ensures the hotfix is also present in any future release branches, avoiding the risk of missing changes when new release branches are created.

Azure DevOps supports cherry‑picking a Pull Request to a different branch, allowing immediate deployment of changes to production while keeping the main branch up‑to‑date.

After merging, the change is deployed to a small set of users (canary), then to early adopters, and finally to all users, with continuous monitoring to ensure no regressions.

Summary

The Release Flow branch model is the core of Microsoft Azure DevOps’s development methodology. It enables a simple, trunk‑based strategy that supports large‑scale online services, eliminates deployment‑queue bottlenecks, and lets engineers focus on delivering value.

Release Flow allows Microsoft to deploy new features across data centers in a regular, coordinated manner, ensuring rapid, safe, and reliable delivery despite the massive number of developers working in a shared codebase.