Fly.io is a public cloud platform that runs applications as lightweight virtual machines (Fly Machines) in data centers around the world, so apps can sit close to their users.
You package an app as a Docker image, deploy it with the flyctl command-line tool and choose which regions it runs in. Fly Machines boot fast, can stop when idle and are controllable through an API, which makes Fly.io popular for globally distributed apps, sandboxes and AI agent workloads.
Key features
- Deploy any Docker image with the flyctl CLI
- Fly Machines: fast-booting micro-VMs controllable through the Machines API
- Many regions worldwide with Anycast networking and a shared IPv4 plus IPv6 per app
- Managed Postgres with automated backups and connection pooling
- Persistent volumes and snapshots
- Sprites for agent sandboxes, and a Fly MCP server for AI agents
- Private networking between apps
Who it's for
Fly.io suits developers and teams that want low-latency, multi-region apps, fine control over VMs and usage-based billing, without managing raw cloud infrastructure.
Common use cases
- Running a web app in several regions close to users
- Hosting Phoenix, Rails, Django or Node apps
- Spinning up on-demand sandboxes for AI agents
- Running managed Postgres next to your app
Pricing
Fly.io bills by usage, per second for compute and by provisioned capacity for storage. Its pricing page lists:
- Machines: from about $2.19 per month for shared-cpu-1x with 256 MB, up to performance presets of several hundred dollars per month.
- Volumes: $0.15 per GB per month. Snapshots: $0.08 per GB per month after the first 10 GB.
- Managed Postgres: plans from $38 per month (Basic).
- Egress: from $0.02 per GB in North America and Europe.
Community support is free, and paid support plans are available.
Alternatives
- Render: managed PaaS for web services and databases
- Railway: usage-based app hosting with simple deploys
- Modal: serverless cloud for AI and GPU workloads
FAQ
Is Fly.io free?
Fly.io has no permanent free plan; it uses pay-as-you-go billing, and small apps can cost only a few dollars per month.
What is Fly.io used for?
Fly.io is used to run Docker-based apps and databases on fast-booting VMs in regions around the world.
Fly.io vs Render: which should I choose?
Fly.io offers multi-region micro-VMs and fine-grained control, while Render provides a simpler managed PaaS experience.
Does Fly.io support PostgreSQL?
Yes. Fly.io offers Managed Postgres, with plans starting at $38 per month.
How does Fly.io billing work?
Compute is billed per second while machines run, storage is billed on provisioned capacity, and egress is billed per GB by region.
Can AI agents use Fly.io?
Yes. Fly.io offers Sprites for agent sandboxes and a Fly MCP server that lets agents manage Fly resources.