Case Study: Upgrading a Rails 5.2 App to 7.1 in 6 Weeks

Upgrading a Rails application across four major versions is one of the most challenging tasks in Rails maintenance. Here's how we did it for a client in just six weeks.

The Challenge

Our client had a production Rails 5.2 application that was critical to their daily operations. They had been deferring upgrades for years due to feature pressure, and the gap had grown to the point where it felt overwhelming.

The application had:

• 60+ gems, many of which were outdated or abandoned
• No automated test suite for critical business flows
• Custom authentication that depended on deprecated Rails APIs
• A legacy frontend using jQuery and CoffeeScript

The Strategy

Rather than attempting a "big bang" upgrade, we used a phased approach:

1. Phase 1: Preparation (Week 1). Full codebase audit, dependency analysis, and test coverage gap analysis. We added integration tests for the most critical user flows.
2. Phase 2: Ruby Upgrade (Week 2). Upgraded from Ruby 2.5 to 3.2, which was a prerequisite for Rails 7.1. This alone fixed several compatibility issues.
3. Phase 3: Incremental Rails Upgrades (Weeks 3-5). We went 5.2 → 6.0 → 6.1 → 7.0 → 7.1, resolving deprecations and incompatibilities at each step. Each intermediate version was validated with the full test suite before proceeding.
4. Phase 4: Modernization (Week 6). Updated configuration to use Rails 7.1 defaults, migrated to Zeitwerk autoloading, and implemented modern security defaults.

The Results

• Completed in 6 weeks (vs. the estimated 12-16 weeks the client had budgeted)
• Zero production incidents during or after the upgrade
• 40% improvement in page load times due to updated caching and connection pooling
• Eliminated 23 known security vulnerabilities from outdated dependencies
• Reduced monthly maintenance overhead by 60%

Key Takeaways

Incremental upgrades are less risky than big-bang approaches. Each intermediate version gave us a known-good state to fall back to, and the discipline of fixing deprecations at each step prevented the accumulation of technical debt.

The most important investment was test coverage. Without adequate tests, we would have been making changes blind. With them, we could move fast with confidence.

If your application is multiple versions behind, don't let the gap intimidate you. A structured, phased approach can get you to the latest Rails version faster than you think.