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100 — Introduction & Core Concepts

What is Fly.io?

Fly.io is a developer-first deployment platform that removes infrastructure complexity while giving you full control over compute. At its heart, it runs your code on Fly Machines — hardware-isolated VMs built on KVM — deployed close to your users across a global network.

Core Concepts

1. Fly Machines

A Fly Machine is the fundamental unit of compute on Fly.io.

  • Built on KVM hardware virtualization (not just containers)
  • Starts in ~300ms — fast enough to boot on demand per HTTP request
  • Runs any OCI-compatible container image
  • Billed per second for CPU + memory consumed
  • Can be paused when idle and resumed instantly
Your App Container
       ↓
  Fly Machine (KVM VM)
       ↓
  Fly.io Metal (bare-metal servers)
       ↓
  Region (e.g., ams, lhr, syd, iad)

2. Fly Apps

A Fly App is a named, logical grouping of Machines and their associated config, networking, and secrets. One app can run many machines.

3. Fly Organizations

An Organization is the billing and access control boundary. Teams share an org; personal projects live in your personal org.

4. Regions

Fly.io operates in 18+ regions worldwide (e.g., ams = Amsterdam, lhr = London, syd = Sydney, iad = Washington DC). You choose which regions your Machines run in.

5. fly.toml

The configuration file for a Fly App. Lives at the root of your project. Defines build settings, services, ports, health checks, scaling, and more.

6. flyctl (the CLI)

The primary way to interact with Fly.io. Install it, log in, and use commands like fly launch, fly deploy, fly status, fly logs.

Architecture Overview

Developer
   │
   ▼
flyctl / CI pipeline
   │
   ▼ fly deploy
Fly Build System (Dockerfile → OCI image)
   │
   ▼
Fly Registry (private image registry)
   │
   ▼
Fly Machines (KVM VMs, per region)
   │
   ▼
Fly Anycast Network → Users worldwide

Key Differentiators vs. Other Platforms

Feature Fly.io Heroku AWS ECS
VM startup time ~300ms Seconds Minutes
Hardware isolation KVM Container Container
Global deployment Built-in Add-on Manual
Pricing model Per-second Per-dyno Per-hour
Postgres Managed Managed DIY
Private networking Built-in WireGuard No VPC
Dockerfile support Native Buildpacks Native

Mental Model

Think of Fly.io as "your own mini cloud, managed for you":

  • You bring a Dockerfile (or use their buildpacks)
  • They handle the global network, certificates, routing, and hardware
  • You control the regions, scaling, and configuration
  • Machines are ephemeral by default but can use Volumes for persistence

Next Steps

→ Continue to 200 — Installation & CLI (flyctl)