25+ Real-World Rails Upgrade Questions (And the Answers Devs Actually Need)

Source: Dev.to

Why upgrade?

• Security – Older Rails versions stop receiving patches, exposing your app.
• Performance – Newer versions bring better performance and tooling.
• Compatibility – Modern gems often require recent Rails releases.
• Maintenance – Reduces long‑term technical debt and makes onboarding easier.

Assessing the complexity

The effort depends on several factors:

• 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• The number of outdated or incompatible gems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.

Upgrade order

1. Upgrade Ruby first – Newer Rails versions usually require a minimum Ruby version.
2. Upgrade Rails step‑by‑step – Avoid skipping major versions; upgrade one major version at a time.

Common breakpoints

• 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 that rely on undocumented Rails internals

Upgrade strategy

• Avoid large 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.

Dependency cleanup

When you encounter an unmaintained gem, you have three choices:

1. Replace it with an alternative.
2. Fork and patch it internally.
3. Remove it if it’s no longer needed.

Upgrades are an ideal time to clean up dependencies; fewer gems mean smoother future upgrades.

Testing critical workflows

For large apps with complex logic:

• Test all critical workflows (billing, imports, jobs).
• Watch SQL logs for new query patterns.
• Run load tests if the app handles millions of records.
• If a component is too risky, consider isolating it behind an API/service during the upgrade.

Adding safety nets

Before starting the upgrade, add basic tests around your most important workflows:

• Snapshot tests to capture current outputs.
• Request recordings using tools like VCR.
• Smoke tests for critical functionality.
• Feature tests for key user flows.

Start with high‑level system tests, use manual QA where needed, and deploy often to staging.

Legacy JavaScript and assets

Rails upgrades do not prevent legacy JavaScript from working, but older UJS conventions or Sprockets‑based assets may need patching. If you migrate to importmaps, ESBuild, or Webpacker, treat it as a parallel track rather than tying it to the Rails core upgrade.

Configuration migration

Older apps using secrets.yml or environment‑variable‑only configs must transition to config/credentials.yml.enc. Rails provides generators and merges environment‑specific files; just ensure consistent master‑key handling across environments.

ActiveStorage and file uploads

ActiveStorage has improved significantly. When moving from Paperclip or CarrierWave, perform the migration before or after the Rails upgrade—not during—to avoid additional complexity.

Dashboard and admin gems

Dashboard gems that depend heavily on internal Rails helpers may need updating. Usually upgrading the gem to its latest version resolves issues; in rare cases, patch deprecated helper usage.

ActionCable and Redis adapters

Expect updated Redis adapters, better concurrency, and cleaner configuration. If you use older subscription identifiers or custom middleware, inspect for deprecations. Most modern ActionCable setups migrate cleanly.

Callbacks and internal behavior

As Rails evolves, certain callbacks (e.g., after_initialize, around_validation) may change behavior. You’ll see warnings early; refactor to service objects or move logic into ActiveModel callbacks aligned with new conventions.

Risks of skipping versions

Skipping multiple major versions compounds technical debt and hides deprecated behaviors until they break everything at once. Incremental deprecation warnings are lost, and the cost and risk rise exponentially.

Database adapters

Legacy apps using older versions of mysql2, pg, or mongoid may face adapter‑breaking changes (SSL defaults, timezone rules, connection handling). Upgrade these dependencies separately and validate connection pooling behavior.

CI/CD pipeline considerations

Your CI pipeline must upgrade Ruby versions, system dependencies (Node, Yarn, Redis), and caching strategies. Outdated build images or broken Dockerfiles are common discoveries; refresh the pipeline before the upgrade to reduce noise.

Timeline estimates

• 50k–200k LOC apps: 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.

Performance benchmarking

Benchmark before and after the upgrade. 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 often caused by changes in ActiveRecord behavior or caching layers.

Bottom line

Upgrading Rails can seem daunting, but with a systematic approach—upgrading Ruby first, moving through major versions one at a time, cleaning up dependencies, adding safety‑net tests, and monitoring performance—you can manage the process confidently and reap benefits such as stronger security, better performance, reduced maintenance costs, and happier developers.