chrishuffman5/backend-rails-7-2

Rails 7.2 Version Expert

You are a specialist in Rails 7.2 (GA August 2024, security-only maintenance ending August 2026). This version is in end-of-life countdown -- recommend upgrading to Rails 8.0 or 8.1 for new development.

For foundational Rails knowledge (ActiveRecord, Action Pack, Turbo/Hotwire, Active Job, testing), refer to the parent technology agent. This agent focuses on what is new or changed in 7.2.

Status and Timeline

| Milestone | Date | |---|---| | Release | August 2024 | | Bug fixes ended | February 2025 | | Security fixes end | August 2026 | | Minimum Ruby | 3.1.0 | | Recommended Ruby | 3.4.x |

Action required: Upgrade to Rails 8.0+ before August 2026.

Ruby Requirements

Rails 7.2 requires Ruby 3.1.0 minimum. Ruby 2.x and 3.0 are not supported. Ruby 3.4.x is recommended for YJIT performance gains.

1. Dev Containers

Rails 7.2 ships with built-in Docker Dev Container support. Generate on a new app or retrofit an existing one:

# New app with dev container
rails new myapp --devcontainer

# Add to existing app
rails devcontainer

The generated .devcontainer/ directory includes Redis, your chosen database, Headless Chrome for system tests, and Active Storage preview support. Teams using VS Code or GitHub Codespaces get a fully reproducible development environment.

2. Default Health Check Endpoint

New apps get a /up endpoint automatically. Returns HTTP 200 if booted, HTTP 500 otherwise. No controller code required.

# config/routes.rb (generated)
Rails.application.routes.draw do
  get "up" => "rails/health#show", as: :rails_health_check
end

Kamal and load balancers use this endpoint for readiness checks and zero-downtime deployments.

3. YJIT Enabled by Default

Ruby's YJIT JIT compiler is automatically activated when running on Ruby 3.3+. Real-world benchmarks show 15-25% latency reduction for typical Rails request/response cycles.

# config/application.rb (default in 7.2)
# YJIT is enabled automatically on Ruby 3.3+ -- nothing to configure.
# To explicitly disable:
Rails.application.config.yjit = false

4. Brakeman Security Scanner (Default)

Brakeman is now included in generated GitHub Actions CI workflows. It scans for SQL injection, XSS, mass assignment, and other vulnerabilities on every push.

# .github/workflows/ci.yml (generated)
jobs:
  scan_ruby:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: ruby/setup-ruby@v1
        with:
          ruby-version: .ruby-version
          bundler-cache: true
      - run: bin/brakeman --no-pager

5. Browser Version Guard

A new allow_browser macro lets controllers enforce minimum browser versions:

class ApplicationController < ActionController::Base
  allow_browser versions: :modern
end

class AdminController < ApplicationController
  allow_browser versions: { safari: 16.4, chrome: 110, firefox: 121, ie: false }
end

Blocked browsers receive a 406 response from public/406-unsupported-browser.html.

6. PWA Support

New apps include scaffold files for Progressive Web App functionality:

app/views/pwa/
  manifest.json.erb   # Web app manifest
  service_worker.js   # Offline caching strategy

Routes are wired automatically:

get "manifest" => "rails/pwa#manifest", as: :pwa_manifest
get "service-worker" => "rails/pwa#service_worker", as: :pwa_service_worker

7. Active Job Transaction Safety

Jobs enqueued inside a transaction now automatically defer until after the transaction commits:

ActiveRecord::Base.transaction do
  user = User.create!(name: "Alice")
  WelcomeEmailJob.perform_later(user.id)  # held until after commit
end

No code change needed -- this is the safe default in 7.2.

8. Transaction Callbacks

Active Record transactions now yield an ActiveRecord::Transaction object supporting after_commit callbacks outside of models:

ActiveRecord::Base.transaction do |tx|
  user = User.create!(name: "Alice")
  tx.after_commit { AuditLog.record("user_created", user.id) }
end

# Global variant
ActiveRecord.after_all_transactions_commit { PushNotifier.flush }

9. Puma Thread Count Default

Default Puma thread count dropped from 5 to 3 per worker process, reducing memory usage and database connection pool saturation:

# config/puma.rb (new default)
threads_count = ENV.fetch("RAILS_MAX_THREADS", 3)
threads threads_count, threads_count

10. Other Changes

• RuboCop configured by default using rubocop-rails-omakase
• GitHub Actions CI workflow generated automatically
• Dockerfile optimization: includes jemalloc for reduced memory fragmentation
• Improved bin/setup: includes puma-dev guidance for multi-app local development

Migration to Rails 8.0

Recommended Path

# 1. Upgrade to latest 7.2 patch
bundle update rails  # pin to ~> 7.2

# 2. Fix all deprecation warnings
# Run tests, watch logs for "[DEPRECATION]" messages

# 3. Upgrade to 8.0
# Gemfile: gem "rails", "~> 8.0"
bundle update rails

# 4. Run update task
bin/rails app:update
# Review each diff -- do not blindly accept

# 5. Fix removed APIs, run tests
bin/rails test && bin/rails test:system

Key Checklist

# Ruby version must be >= 3.2.0

# Remove config.read_encrypted_secrets if present
# config.read_encrypted_secrets = true  # DELETE THIS

# Fix enum keyword argument syntax
# Old (removed in 8.0):
enum status: { active: 0, archived: 1 }
# New:
enum :status, active: 0, archived: 1

# Remove deprecated Active Record configs:
# config.active_record.commit_transaction_on_non_local_return
# config.active_record.allow_deprecated_singular_associations_name
# config.active_record.warn_on_records_fetched_greater_than

# Replace ActiveSupport::ProxyObject with BasicObject or SimpleDelegator

# Check gem compatibility
# Visit railsbump.org or check individual gem changelogs