How it works
Run fly launch in a project and Fly.io builds a container image, then starts it as Fly Machines (fast-booting micro virtual machines built on Firecracker) in the regions you choose. Apps get a global anycast address, private networking between machines, persistent volumes and managed Postgres. Machines can stop when idle and start again on the next request.
It suits apps that need a real long-running server, such as WebSocket services, background workers or SQLite on a volume, spread across regions. You handle more yourself than on Render or Heroku: sizing machines, placing volumes and planning failover. New accounts get a short trial rather than a free allowance, and pricing is purely usage-based.
Fly.io pros and cons
Pros
- Runs any Docker image, in many regions at once
- Per-second billing, and machines can stop when idle
- Real servers, so WebSockets, workers and volumes all work
- Private networking between apps and regions built in
Cons
- No free tier for new accounts, only a short trial
- More operations work than simpler platforms
- Each volume lives on one machine, so redundancy is up to you
When to use Fly.io
Pick it when
- Apps with users in several regions that need low latency
- Long-running servers, WebSockets and background workers
- Teams comfortable with Docker and a command-line workflow
Skip it when
- You want a free tier, or no operations work at all
Fly.io pricing
Pay as you go
Billed by the second. The smallest machine (shared CPU, 256 MB) is about $2 a month if always on; volumes are $0.15 per GB-month and egress starts at $0.02 per GB. New accounts get a short trial.
Fly.io pricing page (opens in a new tab)Approximate, checked September 2026.What the other tools cost
Fly.io vs the alternatives
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