Deployment Strategies

+15 Mana ✨
Flipper Feature Flags(GITHUB)

Introduction

Different deployment strategies balance speed, safety, and complexity. From simple rolling deploys to canary releases, choosing the right strategy depends on your risk tolerance and infrastructure.

Key Concepts

  • Rolling Deploy: Update servers one at a time — Kamal's default strategy. Some servers run old code while others run new code during the transition.
  • Blue-Green Deploy: Two identical environments — deploy to the inactive one, then swap traffic. Instant rollback by swapping back.
  • Canary Deploy: Route a small percentage of traffic to the new version first, monitor for errors, then roll out fully.

Real World Context

A SaaS company with 10,000 active users uses canary deployments to route 5% of traffic to new code first. If error rates spike, they roll back instantly without affecting 95% of users.

Deep Dive

Rolling Deploy (Kamal Default)

Kamal deploys to one server at a time:

yaml
# config/deploy.yml
servers:
  web:
    hosts:
      - web1.example.com
      - web2.example.com
      - web3.example.com
bash
kamal deploy  # Deploys to each host sequentially

Blue-Green with Kamal Destinations

yaml
# config/deploy.production.yml
servers:
  web:
    hosts:
      - blue.example.com
      - green.example.com
bash
# Deploy and verify
kamal deploy --destination production
curl https://myapp.com/health

Feature Flags

ruby
# Gemfile
gem 'flipper'
gem 'flipper-active_record'

# Usage
if Flipper.enabled?(:new_checkout, current_user)
  render 'checkout/new'
else
  render 'checkout/legacy'
end

# Enable for percentage of users
Flipper.enable_percentage_of_actors(:new_checkout, 10)

Rollback

bash
# Kamal auto-rolls back on health check failure
# Manual rollback:
kamal rollback

Common Pitfalls

  1. Deploying without feature flags for risky changes — A feature flag lets you disable a broken feature without rolling back the entire deploy.
  2. Not monitoring after deploy — Watch error rates and response times for 15-30 minutes after every deploy.

Best Practices

  1. Use rolling deploys for most changes — Kamal's default is safe and simple for the majority of deploys.
  2. Use feature flags for high-risk features — Wrap new features in flags so you can disable them instantly without redeploying.

Summary

  • Rolling deploys (Kamal's default) update servers sequentially.
  • Blue-green deployments allow instant rollback by swapping environments.
  • Feature flags decouple deployment from feature activation.
  • Always monitor error rates and response times after deploying.

Code Examples

ruby
# Feature flags decouple deploy from activation
if Flipper.enabled?(:new_pricing, current_user)
  # New pricing logic
else
  # Existing pricing logic
end

# Gradually roll out
Flipper.enable_percentage_of_actors(:new_pricing, 5)   # 5%
Flipper.enable_percentage_of_actors(:new_pricing, 25)  # 25%
Flipper.enable_percentage_of_actors(:new_pricing, 100) # Everyone
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