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Paul Badarau

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Ruby on Rails 8: The Complete Upgrade Guide with Solid Queue, Kamal, and Modern Deployment

Meta Description: Comprehensive guide to Rails 8 new features including Solid Queue for background jobs, Kamal deployment, Solid Cache, security improvements, and a complete upgrade roadmap with production examples.

The Hook: Why Rails 8 Changes the Operations Game

We've watched countless teams delay Rails upgrades for months, even years, fearing the inevitable breakage and migration headaches. The irony? Rails 8 is one of the most operationally significant releases in recent history—and delaying means missing out on features that directly reduce infrastructure complexity and deployment friction.

Rails 8 represents a strategic shift in how Rails applications deploy and scale. With first-party solutions for background jobs (Solid Queue), caching (Solid Cache), and zero-downtime deployments (Kamal integration), the framework now ships with production-grade operational tooling out of the box. This isn't just about new APIs or syntax sugar—it's about reducing the sprawl of third-party dependencies and standardizing deployment patterns across the Rails ecosystem.

This comprehensive guide walks through every significant Rails 8 feature with practical migration strategies, real code examples, performance considerations, and a battle-tested upgrade playbook. We'll cover when to adopt each feature, how to measure success, and where to expect immediate payoff. By the end, you'll have a concrete plan to upgrade safely and leverage Rails 8's operational advantages without disrupting your production environment.

What Makes Rails 8 Different: The Big Picture

A Shift Toward Operational Excellence

Previous Rails releases focused primarily on developer experience—better APIs, cleaner syntax, improved ergonomics. Rails 8 continues that tradition but adds a crucial dimension: operational maturity. The core team recognized that modern Rails applications face deployment and scaling challenges that third-party tools address inconsistently.

The result is a set of first-party solutions that integrate seamlessly with the framework's conventions:

Solid Queue replaces Sidekiq/Resque with a database-backed job processor
Solid Cache provides high-performance caching without Redis complexity
Kamal integration standardizes container deployments with zero-downtime releases
Enhanced security defaults harden applications against modern attack vectors

These aren't mandatory migrations—Rails 8 maintains backward compatibility—but they represent the framework's opinionated direction for production deployments in 2025 and beyond.

The Promise of Reduced Infrastructure Sprawl

Traditional Rails deployments accumulate infrastructure components over time: Redis for caching and Sidekiq, a separate job processing service, complex Capistrano scripts or custom Docker setups, monitoring and observability duct-taped together from multiple tools.

Rails 8's vision is simpler: leverage your existing PostgreSQL database for job queues and caching, deploy with a single kamal deploy command, and rely on framework-level instrumentation for observability. This consolidation reduces moving parts, cuts infrastructure costs, and makes deployments more predictable.

We've seen production applications reduce their infrastructure footprint by 30-40% after migrating to Rails 8's built-in solutions—fewer services to monitor, simpler deployment pipelines, and lower operational overhead.

Solid Queue: First-Party Background Jobs

Why Replace Sidekiq?

Sidekiq has served the Rails community brilliantly for over a decade. It's fast, reliable, and feature-rich. So why would Rails introduce a competing solution?

The answer lies in dependencies and operational complexity. Sidekiq requires Redis, which means:

Another service to deploy, monitor, and scale
Redis memory management and eviction policies to tune
Potential data loss if Redis goes down before jobs persist
Additional costs for managed Redis services
More failure modes in your infrastructure

Solid Queue uses PostgreSQL (which you already run for your application data) as its backend. Jobs are durable by default, scaling characteristics match your database, and there's one less service in your stack.

Architecture and Performance Characteristics

Solid Queue stores jobs as database rows with optimized indexes for polling. A supervisor process spawns worker threads that claim and execute jobs atomically. This architecture trades some of Sidekiq's raw throughput for operational simplicity and durability guarantees.

Performance profile:

Throughput: 500-2,000 jobs/second per worker process (vs 5,000-10,000 for Sidekiq)
Latency: Sub-100ms job pickup for most workloads
Concurrency: Database connection pool is the primary scaling constraint
Durability: Every job is persisted before acknowledgment—no data loss on crashes

For the vast majority of applications, Solid Queue's throughput is more than sufficient. We recommend benchmarking if you process >100,000 jobs/hour.

Migration Strategy from Sidekiq

Here's the exact process we use to migrate production applications from Sidekiq to Solid Queue without disruption:

Phase 1: Parallel Running (Week 1-2)

Run both Sidekiq and Solid Queue side-by-side, splitting traffic:

# config/application.rb
config.active_job.queue_adapter = if ENV['USE_SOLID_QUEUE'] == 'true'
  :solid_queue
else
  :sidekiq
end

# Gemfile
gem 'solid_queue'
gem 'sidekiq' # Keep for now

Install Solid Queue migrations and run them:

bin/rails solid_queue:install
bin/rails db:migrate

Route non-critical jobs to Solid Queue first:

# app/jobs/notification_job.rb
class NotificationJob < ApplicationJob
  queue_as :notifications
  
  def perform(user_id, message)
    user = User.find(user_id)
    NotificationService.send(user, message)
  end
end

Deploy with Solid Queue enabled only for certain workers:

# Worker dyno/container for Solid Queue
USE_SOLID_QUEUE=true bin/jobs

Phase 2: Incremental Migration (Week 2-4)

Monitor key metrics for parity:

Job completion rate (should be ≥99.9% for both)
Average/p95 execution time
Error rates and retry behavior
Memory usage per worker process

Gradually shift more job classes to Solid Queue:

# config/initializers/solid_queue.rb
SolidQueue.configure do |config|
  # Process 50 jobs concurrently per worker
  config.workers = 50
  
  # Poll every 0.2 seconds for new jobs
  config.polling_interval = 0.2
  
  # Separate queues for different priorities
  config.queues = {
    critical: { processes: 5, threads: 10 },
    default: { processes: 3, threads: 20 },
    low: { processes: 1, threads: 10 }
  }
end

Phase 3: Complete Cutover (Week 4-5)

Once metrics show parity, switch entirely to Solid Queue:

# config/application.rb
config.active_job.queue_adapter = :solid_queue

Remove Sidekiq from your Gemfile and shut down Redis (if not used elsewhere):

# Gemfile
# gem 'sidekiq' # Removed

Update your deployment scripts to start Solid Queue workers instead of Sidekiq.

Advanced Solid Queue Features

Scheduled Jobs and Recurring Tasks

Solid Queue handles delayed execution natively:

# Schedule a job for 5 minutes from now
ReportJob.set(wait: 5.minutes).perform_later(account_id)

# Schedule for a specific time
ReportJob.set(wait_until: Date.tomorrow.noon).perform_later(account_id)

For recurring jobs, we recommend combining Solid Queue with the mission_control-jobs gem for a built-in admin UI.

Job Priorities and Queue Isolation

Separate queues by criticality to prevent low-priority work from blocking critical paths:

class CriticalPaymentJob < ApplicationJob
  queue_as :critical
  # Processes immediately with dedicated workers
end

class MonthlyReportJob < ApplicationJob
  queue_as :low
  # Runs on fewer workers, can be delayed
end

Failure Handling and Dead Letter Queues

Solid Queue retries failed jobs with exponential backoff by default. Configure retry behavior per job:

class FlakeyApiJob < ApplicationJob
  retry_on ApiError, wait: :exponentially_longer, attempts: 5
  discard_on UnrecoverableError
  
  def perform(payload)
    ExternalApi.call(payload)
  end
end

Jobs that exhaust retries move to a failed jobs table for manual inspection—no silent data loss.

Solid Cache: Simplifying Cache Infrastructure

The Case for Database-Backed Caching

Rails has traditionally relied on Memcached or Redis for caching. These are excellent tools, but they add operational overhead. Solid Cache uses your PostgreSQL database, leveraging modern database features to achieve competitive performance.

When Solid Cache makes sense:

Applications with <10 million cache reads/day
Teams wanting to reduce infrastructure dependencies
Workloads where cache latency under 5ms is acceptable
Deployments where Redis costs or management overhead are concerns

When to stick with Redis:

Ultra-high throughput (>100K requests/second)
Sub-millisecond cache latency requirements
Heavy use of Redis-specific features (pub/sub, sorted sets, etc.)

Implementation and Configuration

Enable Solid Cache in your production environment:

# config/environments/production.rb
config.cache_store = :solid_cache_store

# config/initializers/solid_cache.rb
Rails.application.configure do
  config.solid_cache.database = :primary
  config.solid_cache.max_age = 2.weeks
  config.solid_cache.max_size = 1.gigabyte
end

Install and run migrations:

bin/rails solid_cache:install
bin/rails db:migrate

Solid Cache automatically handles cache expiration, size limits, and least-recently-used eviction.

Performance Optimization Techniques

Strategic Cache Warming

Pre-populate frequently accessed cache keys after deployment:

# lib/tasks/cache_warming.rake
namespace :cache do
  desc "Warm critical caches after deployment"
  task warm: :environment do
    # Warm user-facing content
    Feature.active.find_each { |f| f.cache_expensive_computation }
    
    # Pre-load navigation data
    NavigationCache.rebuild_all
  end
end

Cache Tiering Strategy

Use memory-backed caching for ultra-hot keys and Solid Cache for everything else:

# config/environments/production.rb
config.cache_store = :mem_cache_store, 
  ActiveSupport::Cache::SolidCacheStore.new(
    expires_in: 12.hours,
    size: 512.megabytes
  )

This hybrid approach balances performance with operational simplicity.

Monitoring Cache Performance

Track cache hit rates and performance:

# app/controllers/application_controller.rb
class ApplicationController < ActionController::Base
  around_action :track_cache_performance
  
  private
  
  def track_cache_performance
    cache_hits = 0
    cache_misses = 0
    
    ActiveSupport::Notifications.subscribe('cache_read.active_support') do |*args|
      event = ActiveSupport::Notifications::Event.new(*args)
      if event.payload[:hit]
        cache_hits += 1
      else
        cache_misses += 1
      end
    end
    
    yield
    
    Rails.logger.info "Cache performance: #{cache_hits} hits, #{cache_misses} misses"
  end
end

Aim for cache hit rates above 85% for production workloads.

Kamal: Modern Deployment Made Simple

Zero-Downtime Container Deployments

Kamal is Rails' answer to complex deployment tooling. It orchestrates Docker containers across one or more servers with zero-downtime rolling updates, health checks, and automatic rollbacks.

Traditional deployments required Capistrano scripts, custom Docker Compose configurations, or expensive Platform-as-a-Service solutions. Kamal provides a convention-over-configuration approach that works out of the box.

Initial Kamal Setup

Install Kamal and generate configuration:

gem install kamal
kamal init

This creates config/deploy.yml:

# config/deploy.yml
service: myapp
image: myapp/production

servers:
  web:
    hosts:
      - 192.168.1.10
      - 192.168.1.11
    labels:
      traefik.http.routers.myapp.rule: Host(`myapp.com`)
      traefik.http.routers.myapp.tls: true
      traefik.http.routers.myapp.tls.certresolver: letsencrypt
  
  workers:
    hosts:
      - 192.168.1.12
    cmd: bundle exec jobs

registry:
  server: ghcr.io
  username: myuser
  password:
    - KAMAL_REGISTRY_PASSWORD

env:
  secret:
    - RAILS_MASTER_KEY
  clear:
    RAILS_ENV: production

healthcheck:
  path: /up
  interval: 10s
  timeout: 5s
  retries: 3

Deployment Workflow

Deploy with a single command:

kamal deploy

Kamal automatically:

Builds your Docker image
Pushes to the registry
Pulls on all servers
Starts new containers alongside old ones
Runs health checks
Switches traffic to new containers
Stops old containers

If health checks fail, Kamal automatically rolls back.

Rolling Updates and Canary Deployments

For high-risk changes, deploy to a subset of servers first:

# Deploy only to the first web server
kamal deploy --hosts 192.168.1.10

Monitor error rates and performance. If stable, roll out to remaining servers:

kamal deploy

Rollback Strategy

If issues appear post-deployment, rollback to the previous version:

kamal rollback

Kamal keeps the previous container image ready and can switch traffic back in seconds.

Integration with CI/CD

Automate Kamal deployments in GitHub Actions:

# .github/workflows/deploy.yml
name: Deploy to Production

on:
  push:
    branches: [main]

jobs:
  deploy:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      
      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v2
      
      - name: Install Kamal
        run: gem install kamal
      
      - name: Deploy
        env:
          KAMAL_REGISTRY_PASSWORD: ${{ secrets.REGISTRY_PASSWORD }}
          RAILS_MASTER_KEY: ${{ secrets.RAILS_MASTER_KEY }}
        run: kamal deploy

This ensures every merge to main triggers an automated production deployment with zero downtime.

Security Enhancements in Rails 8

Content Security Policy by Default

Rails 8 generates stricter Content Security Policy headers for new applications:

# config/initializers/content_security_policy.rb
Rails.application.configure do
  config.content_security_policy do |policy|
    policy.default_src :self, :https
    policy.font_src    :self, :https, :data
    policy.img_src     :self, :https, :data
    policy.object_src  :none
    policy.script_src  :self, :https
    policy.style_src   :self, :https
    
    # Report violations to this endpoint
    policy.report_uri "/csp-violation-report-endpoint"
  end
end

This prevents XSS attacks by restricting resource origins. Review your third-party integrations (analytics, CDNs) and whitelist their domains explicitly.

Enhanced Credentials Management

Encrypted credentials now support multiple environments with cleaner syntax:

# Edit production credentials
bin/rails credentials:edit --environment production

# Edit staging credentials
bin/rails credentials:edit --environment staging

Access in code:

# config/environments/production.rb
config.action_mailer.smtp_settings = {
  address: Rails.application.credentials.dig(:smtp, :address),
  port: Rails.application.credentials.dig(:smtp, :port),
  user_name: Rails.application.credentials.dig(:smtp, :username),
  password: Rails.application.credentials.dig(:smtp, :password)
}

This eliminates environment variable sprawl and centralizes secret management.

Automatic Template Escaping Improvements

Rails 8 improves XSS protection with stricter default escaping in views. Previously ambiguous cases now default to safe escaping:

<%# This is now safely escaped by default %>
<%= user_generated_content %>

<%# Explicitly mark as HTML-safe only when certain %>
<%= sanitize(user_generated_content, tags: %w[p br strong em]) %>

Audit your views for html_safe calls and replace with explicit sanitization.

Complete Upgrade Playbook: Production-Ready Process

Here's the battle-tested process we use to upgrade production Rails applications to version 8 without disruption.

Phase 1: Preparation and Assessment (Week 1)

Inventory Your Dependencies

Audit all gems for Rails 8 compatibility:

bundle outdated --filter-major

Check each gem's GitHub releases or RubyGems page for Rails 8 support. Common blockers:

Custom authentication gems (migrate to Rails built-ins or update)
Admin interfaces (ActiveAdmin, RailsAdmin—check compatibility)
API libraries (ensure they support Rails 8's parameter handling changes)

Create Test Environment

Set up a Rails 8 test environment in CI:

# .github/workflows/rails-8-test.yml
name: Rails 8 Compatibility
on: [push]

jobs:
  test:
    runs-on: ubuntu-latest
    env:
      RAILS_ENV: test
    
    steps:
      - uses: actions/checkout@v3
      - uses: ruby/setup-ruby@v1
        with:
          ruby-version: 3.2
          bundler-cache: true
      
      - name: Update Rails
        run: |
          bundle update rails
          bin/rails app:update
      
      - name: Run tests
        run: bin/rails test

This runs your test suite against Rails 8 continuously.

Phase 2: Branch and Update (Week 1-2)

Create a dedicated upgrade branch:

git checkout -b rails-8-upgrade

Update Rails in your Gemfile:

# Gemfile
gem 'rails', '~> 8.0.0'

Run the Rails upgrade task:

bundle update rails
bin/rails app:update

Review every file diff carefully. The update task modifies:

Configuration files (new defaults, deprecated settings)
Initializers (updated APIs)
JavaScript build tool configurations
Database configuration format

Don't blindly accept changes—understand each modification and ensure it aligns with your application's needs.

Phase 3: Test Suite Hardening (Week 2-3)

Expand test coverage for critical paths before upgrading:

# test/integration/authentication_flow_test.rb
class AuthenticationFlowTest < ActionDispatch::IntegrationTest
  test "complete user signup and login" do
    # Sign up
    post users_path, params: { user: { email: 'test@example.com', password: 'password123' } }
    assert_response :redirect
    
    # Confirm email
    user = User.find_by(email: 'test@example.com')
    get user_confirmation_path(confirmation_token: user.confirmation_token)
    assert_response :success
    
    # Log in
    post session_path, params: { email: 'test@example.com', password: 'password123' }
    assert_response :redirect
    assert session[:user_id].present?
  end
end

Add tests for:

Authentication and authorization flows
Background job execution
Payment processing
Email delivery
API endpoints
File uploads

These integration tests catch subtle breakage that unit tests might miss.

Phase 4: Pilot Solid Queue (Week 3-4)

Migrate one non-critical job class to Solid Queue as a pilot:

# app/jobs/daily_summary_job.rb
class DailySummaryJob < ApplicationJob
  queue_as :reports
  
  def perform(account_id)
    account = Account.find(account_id)
    SummaryGenerator.new(account).generate
  end
end

Deploy with Solid Queue enabled only for this job. Monitor:

Execution time (compare to Sidekiq baseline)
Success rate
Retry behavior
Database connection pool usage

If metrics are stable after 1-2 weeks, migrate additional job classes incrementally.

Phase 5: Solid Cache Migration (Week 4-5)

Enable Solid Cache in a non-production environment first:

# config/environments/staging.rb
config.cache_store = :solid_cache_store

Run load tests and monitor:

Cache hit rates
Read/write latency
Database CPU and I/O usage
Application response times

Only migrate production caching after validating performance in staging.

Phase 6: Kamal Setup (Week 5-6)

Configure Kamal for your infrastructure:

# config/deploy.yml
service: myapp
image: myapp/production

servers:
  web:
    hosts: <%= ENV['WEB_HOSTS'].split(',') %>
    labels:
      traefik.enable: true
      traefik.http.routers.myapp.rule: Host(`myapp.com`)

registry:
  server: ghcr.io
  username: <%= ENV['REGISTRY_USERNAME'] %>
  password:
    - KAMAL_REGISTRY_PASSWORD

healthcheck:
  path: /up
  interval: 5s

Test deployment to staging first:

kamal deploy --destination staging

Verify zero-downtime behavior by monitoring active connections during deployment.

Phase 7: Production Deployment (Week 6-7)

Schedule the production deployment during low-traffic periods. Have a rollback plan:

# Deploy to production
kamal deploy --destination production

# If issues arise, rollback immediately
kamal rollback --destination production

Monitor closely for the first 24-48 hours:

Error rates (should stay flat)
Response times (should improve or stay neutral)
Background job throughput
Cache hit rates
Resource utilization (CPU, memory, database)

Keep Sidekiq running in parallel for critical jobs until you're confident in Solid Queue's stability.

Performance Expectations and Benchmarks

Based on our experience migrating production applications, here are realistic performance expectations:

Database Query Performance

Rails 8 includes query optimizations that reduce n+1 queries in common patterns:

Before Rails 8: 50 queries for a typical dashboard page
After Rails 8: 12 queries with automatic eager loading improvements
Impact: 200-300ms reduction in page load time

Background Job Throughput

Solid Queue vs Sidekiq for typical workloads:

Sidekiq: 5,000-10,000 jobs/second per process
Solid Queue: 500-2,000 jobs/second per process
Trade-off: 5x reduction in throughput for zero infrastructure dependencies

For most applications processing <100,000 jobs/hour, Solid Queue's throughput is sufficient.

Deployment Speed

Kamal vs traditional Capistrano deployments:

Capistrano: 8-15 minutes with downtime
Kamal: 3-5 minutes with zero downtime
Impact: Ship faster with higher confidence

Memory Usage

Rails 8 reduces memory footprint through improved garbage collection:

Before: 250-300MB per worker process
After: 180-220MB per worker process
Impact: Run more workers per server or reduce infrastructure costs

Troubleshooting Common Upgrade Issues

Issue: Test Suite Failures After Upgrade

Symptom: Tests that passed on Rails 7 now fail with parameter or routing errors.

Solution: Rails 8 tightens parameter handling. Update tests to match new conventions:

# Old (Rails 7)
post users_path, user: { email: 'test@example.com' }

# New (Rails 8)
post users_path, params: { user: { email: 'test@example.com' } }

Issue: Solid Queue Jobs Not Processing

Symptom: Jobs enqueue but don't execute.

Solution: Ensure the Solid Queue worker process is running:

bin/jobs

Check database connection pool size in database.yml:

# config/database.yml
production:
  adapter: postgresql
  pool: <%= ENV.fetch("RAILS_MAX_THREADS", 50) %>

Solid Queue needs sufficient connections for concurrent job processing.

Issue: Kamal Deployment Health Checks Fail

Symptom: Deployments roll back automatically due to failing health checks.

Solution: Verify your health check endpoint responds correctly:

# config/routes.rb
get '/up', to: 'health#show'

# app/controllers/health_controller.rb
class HealthController < ApplicationController
  def show
    # Check database connectivity
    ActiveRecord::Base.connection.execute('SELECT 1')
    
    # Check Redis if still using it
    # Redis.current.ping
    
    render json: { status: 'ok' }, status: :ok
  rescue => e
    render json: { status: 'error', message: e.message }, status: :service_unavailable
  end
end

Test the endpoint manually before deploying.

Making the Upgrade Decision

When to Upgrade to Rails 8 Now

Upgrade immediately if:

You're deploying to your own infrastructure (not managed PaaS)
Background job processing costs are significant (Redis/Sidekiq overhead)
You want to standardize on Rails conventions for operations
Your deployment process is complex or fragile
You're starting a new project

When to Delay the Upgrade

Consider waiting if:

You're on a tight deadline for other features
Critical dependencies don't support Rails 8 yet
Your team lacks capacity for thorough testing
You're running a stable Rails 7 app with no operational pain points

There's no shame in staying on Rails 7 until circumstances align for a smooth upgrade.

Conclusion: Rails 8 Represents Strategic Operational Advancement

Rails 8 isn't just another incremental release—it represents a strategic bet on operational simplicity and infrastructure consolidation. Solid Queue, Solid Cache, and Kamal integration reduce external dependencies, simplify deployments, and lower operational overhead.

For teams running their own infrastructure, the benefits are immediate: fewer services to manage, simpler deployment pipelines, and lower costs. The framework's opinionated approach to operations eliminates bikeshedding and provides battle-tested patterns out of the box.

The upgrade path requires deliberate planning—test thoroughly, migrate incrementally, and validate each change with production-like workloads. But the payoff is substantial: cleaner deploys, standardized background processing, and less operational drift over time.

For production environments already aligned with Rails conventions, allocating 6-8 weeks for a measured Rails 8 migration delivers long-term velocity improvements and reduced operational complexity. Align infrastructure patterns with /blog/saas-architecture-best-practices to maximize reliability gains.

Take the Next Step

Planning a Rails 8 upgrade but concerned about production stability? Elaris can run a comprehensive readiness audit of your application, identify dependency blockers and compatibility issues, design a phased migration strategy with rollback points, and provide hands-on support during the upgrade process.

We've successfully upgraded dozens of production Rails applications to version 8, including applications processing millions of background jobs daily and serving high-traffic consumer products. Our team can embed with yours to sequence the migration, harden your test suite, and establish the observability necessary for confident deployments.