Upgrading a Rails app can feel intimidating, even for experienced teams. Between gem compatibility issues, Ruby version bumps, API changes, and legacy code challenges, it’s natural for developers to have a ton of questions.
With nearly two decades of hands-on experience in the Ruby on Rails ecosystem, RailsFactory has seen these challenges up close across hundreds of upgrade projects.
Drawing from that deep, real-world exposure, we’ve gathered the most common Rails upgrade questions (and practical answers) to help you navigate your next upgrade with confidence.
1. Is it really worth upgrading Rails right now?
Yes. The biggest reason is security. Older Rails versions stop receiving patches, which exposes your app. Newer versions also bring better performance, improved tooling, and compatibility with modern gems.
The longer you delay, the harder (and more expensive) the upgrade becomes.
2. How do we figure out the size of the upgrade?
The complexity depends on:
- How many Rails versions you’re behind
- Your current Ruby version
- The number of outdated or incompatible gems
- Legacy patterns in your codebase (Sprockets, old AR syntax, monkey patches)
- Running a Rails upgrade audit or gem compatibility tool quickly reveals blockers.
3. Should we upgrade Ruby or Rails first?
Upgrade Ruby first.
Each Rails version has a minimum Ruby requirement.
Stick to the latest patch version (e.g., 7.0.x → 7.0.latest) so you avoid extra steps later.
4. What usually breaks during a Rails upgrade?
Common breakpoints include:
- Unmaintained or incompatible gems
- Changes in ActiveRecord behavior (NULLs, time zones, queries)
- Autoloading issues when moving to Zeitwerk
- Background jobs/mailers affected by API changes
- Tests relying on undocumented Rails internals
Upgrading step-by-step prevents chaos.
5. How do we reduce risk during the upgrade?
- Avoid version jumps, upgrade one major version at a time
- Pause major feature development temporarily
- Use a staging environment with near-production data
- Deploy in small batches so issues surface early without impacting all users
- Have backups and rollback plans ready
6. What if an old gem doesn’t support the new Rails version?
You typically have three choices:
- Replace it with an alternative
- Fork and patch it internally
- Remove it altogether if it’s no longer needed
Upgrades are the perfect time for dependency cleanup.
7. How do we upgrade a very large Rails app safely?
For big apps with complex logic:
- Test all critical workflows (billing, imports, jobs)
- Watch SQL logs, Rails may generate new query patterns
- Run load tests if your app handles millions of records
- If something is too risky, consider isolating it behind APIs/services as part of the upgrade process
8. Why should I upgrade my Rails app at all?
Because upgrades give you:
- Security patches
- Better performance
- Compatibility with modern Ruby
- Reduced long-term maintenance costs
- Easier onboarding for new developers
Old versions become a liability very quickly.
9. How do I know which Rails version I can directly upgrade to?
Rails does NOT support skipping major versions.
Example path:
5.2 → 6.0 → 6.1 → 7.0 → 7.1
Skipping versions leads to broken APIs, dead gems, and unpredictable behavior.
10. How do I estimate the time/effort needed for the upgrade?
Consider:
- The Rails version gap (more versions behind = more work)
- Number of incompatible or abandoned gems
- Codebase size, complexity, and test coverage
- Presence of custom patches, monkey-patched Rails internals, or legacy patterns (Sprockets, classic autoloading, old callbacks)
A typical major version upgrade can take anywhere from a few days to several weeks, depending on these factors.
11. What are the biggest risks during a Rails upgrade?
- Breaking changes in ActiveRecord & controller APIs
- Gem incompatibilities
- Deprecated Ruby syntax/Ruby language changes (for example: updates to keyword arguments, method signatures, or removed legacy syntax)
- Potential performance regressions
Mitigation: Upgrade in small steps and keep CI/CD tests running.
12. How do we handle gem incompatibilities?
- Check gem release notes
- Replace old gems (e.g., Paperclip → ActiveStorage)
- Fork temporarily if needed
- Remove unused gems
- Fewer dependencies = smoother upgrades.
13. What’s the business value of upgrading now instead of waiting?
- Stronger security
- Faster development & better tooling
- Happier developers (no one wants to work on Rails 4)
- Lower long-term costs
- Avoiding technical debt snowballing
- Upgrades pay for themselves over time.
14. What if my Rails app doesn’t have good test coverage?
You can still upgrade, just more carefully:
Start with high-level system tests for critical workflows
- Use manual QA where needed
- Deploy often to staging
- Upgrade version-by-version
Many legacy apps with zero tests have been upgraded successfully.
15. How do we handle gems that are no longer maintained?
When a dependency becomes unmaintained, the safest path is to either replace it with a modern alternative or fork it internally. During upgrades, stale gems often trigger cascading failures. Most teams choose to migrate to actively maintained libraries, especially for critical functionality like authentication, file uploads, or background jobs.
16. How do Rails upgrades affect background job processors like Sidekiq or Resque?
Upgrading Rails often means upgrading Redis clients, ActiveJob adapters, or middleware. Before upgrading, you should confirm job payload formats, retry logic, and queue naming haven’t changed. Sidekiq generally upgrades smoothly, but older Resque setups may require more restructuring.
17. What’s the best way to upgrade a legacy Rails app that has no test suite?
Before starting the upgrade, add basic tests around your most important workflows. This can include:
- Snapshot tests to capture current outputs
- Request recordings using tools like VCR
- Smoke tests for critical functionality
- Feature tests for key user flows
Once these tests are in place, begin the upgrade incrementally. Skipping this step increases the risk of breaking existing functionality.
18. Can we upgrade Rails if the app still uses jQuery-heavy frontend code?
Absolutely. Rails upgrades don’t prevent legacy JavaScript from working. However, older UJS conventions or Sprockets-based assets may require patching. If you migrate to importmaps, ESBuild, or Webpacker, plan it as a parallel track rather than tying it into the Rails core upgrade.
19. How do we handle encrypted credentials during an upgrade?
Older apps still using secrets.yml or environment-variable-only configs must transition to config/credentials.yml.enc. The upgrade is straightforward: Rails provides generators and merges environment-specific files. You only need to ensure consistent master key handling across environments.
20. What changes should we expect with ActiveStorage during upgrades?
ActiveStorage improved significantly over versions. Older apps may need schema changes, new variants processing, or updates in signed URL generation. If you're switching from Paperclip or CarrierWave, do it before or after the upgrade, not during the time of upgrade.
21. Do Rails upgrades break admin dashboards like ActiveAdmin or RailsAdmin?
Sometimes. These tools depend heavily on internal Rails helpers and form builders. Typically, upgrading the dashboard gem to its latest version solves the issue. In rare cases, patching deprecated helper usage may be required.
22. How do Rails upgrades impact ActionCable setups for real-time features?
Expect updated Redis adapters, better concurrency, and cleaner configuration. If you’re using older subscription identifiers or custom middleware, inspect for deprecations. Most modern ActionCable setups migrate cleanly.
23. Should we upgrade Ruby first or Rails first?
Always upgrade Ruby first, then Rails. A newer Rails version usually expects a certain minimum Ruby version, and Ruby-level performance or syntax changes (like pattern matching) may affect how your code behaves.
24. How do we handle deprecated callbacks or lifecycle hooks?
As Rails evolves, certain callbacks (e.g., after_initialize, around_validation) may change behavior. You’ll see warnings early. Migration involves either refactoring to service objects or moving logic into ActiveModel callbacks aligned with new conventions.
25. What’s the biggest risk with skipping multiple Rails versions at once?
Skipping multiple versions compounds technical debt and hides deprecated behaviors until they break everything at once. You lose the safety of incremental deprecation warnings. The cost and risk rise exponentially with every version skipped.
26. How do we upgrade apps that rely on older ORMs or database drivers?
Legacy apps using older versions of MySQL2, PG, or Mongoid sometimes face adapter-breaking changes. Database drivers often enforce newer SSL defaults, timezone rules, or connection handling standards. Always upgrade these dependencies separately and validate connection pooling behavior.
27. How do Rails upgrades affect CI/CD pipelines?
Your CI pipeline must upgrade Ruby versions, system dependencies (Node, Yarn, Redis), and caching strategies. Many teams discover outdated build images or broken Dockerfiles during upgrades. Refreshing the pipeline before the upgrade reduces noise.
28. How long does a typical Rails upgrade take for medium-sized applications?
For apps in the 50k–200k Line of Code range, expect 3–8 weeks depending on test coverage, gem complexity, and number of versions skipped. Apps with strong test suites finish significantly faster. Apps without tests require more hardening and regression checks.
29. What’s the best way to ensure performance doesn’t regress after an upgrade?
Benchmark before and after. Tools like rack-mini-profiler, Scout, or Skylight help detect slow queries, bloated memory usage, or changed caching behaviors introduced during the upgrade. Performance regressions are usually caused by changes in ActiveRecord behavior or caching layers.
Wrap-Up
Upgrading Rails can seem daunting, but with the right approach, it’s entirely manageable. By planning carefully, upgrading incrementally, testing critical workflows, and keeping dependencies up to date, you can modernize your application safely and efficiently.
Remember, whether your app is small or large, having a structured upgrade plan is the key to reducing risk and ensuring a smoother transition. You can also download and keep our free pre-upgrade checklist handy as you prepare. Always stay proactive, follow best practices, and treat each upgrade as an opportunity to clean up legacy code, adopt modern patterns, and prepare your app for the future.
Hope we’ve covered most of the questions you had in mind. If you’re still weighing your options or want a second opinion on your Rails upgrade path, our team at RailsFactory is always available to help.
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