Zero Downtime Deploys on Fly.io

Deploying code shouldn't feel like defusing a bomb. Ship features during business hours without sweating through your shirt or sending "sorry for the downtime" emails. Your users won't even notice you deployed.

Dive into the docs!
Health Checks

Health Checks: Don't Route Traffic to Broken Things

Here's the secret to zero downtime: we don't send users to your new code until it passes a health check. Configure an endpoint that says "yep, I'm good to go," and we'll ping it before routing traffic. If it fails, the old version keeps running. Some call it revolutionary.

  • HTTP checks for web services (just return a 200)
  • TCP checks for non-HTTP services
  • Configurable intervals and timeouts
  • Grace periods for slow startup
  • Custom headers for auth or routing
  • Smoke checks monitor for ~10s after boot

Pick Your Deployment Strategy (Or Don't, We Have Defaults)

Different apps need different deploy strategies. Rolling updates work great for most things. Canary is perfect when you're nervous. Bluegreen is fast but needs more resources. Immediate is for "I know what I'm doing" emergencies. Choose based on your risk tolerance and coffee intake.

Rolling (default): Replace Machines one at a time. Safe, steady, works everywhere.
Canary: Boot one new Machine first. If it's healthy, proceed with rolling. Your guardrail.
Bluegreen: Boot all new Machines alongside old ones. Switch traffic when ready. Fast but uses 2x resources briefly.
Immediate: Replace everything now, no health checks. For emergencies or when you're feeling brave.
Deployment Strategies

Release Commands: Run Migrations Before You Deploy

Database migrations, cache warming, asset precompilation, whatever needs to happen before your new code goes live. Define a release_command and we'll run it once before deploying. If it fails, the deploy stops. No "oops forgot to migrate" moments.

Runs once before deployment starts
Perfect for database migrations
Fails the deploy if the command fails
Configure in fly.toml with one line

Read the Docs

Seamless Deployments Guide

The complete guide to zero downtime deploys on Fly.io

Deploy Configuration

Configure deployment strategies in fly.toml

Health Checks

Set up HTTP and TCP health checks for your services

Release Commands

Run migrations and setup tasks before deployment

Deploy Whenever You Want

Deploy Anytime

Remember when "deploy Friday" was a career-limiting move? With zero downtime deploys, you can ship code when it's ready. Health checks, rolling updates, and automatic rollbacks mean you can push at 3pm on a Friday and still sleep well. Live dangerously (but safely).

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