What Is Fly.io? Run Containers Close to Users
Fly.io runs your application in lightweight Firecracker microVMs deployed to regions around the world, so it executes close to your users rather than in one data center.
Fly.io takes your container and runs it as a microVM (called a Machine) in any of its global regions. The pitch is a simple deploy experience with geographic distribution: your app, full-stack and with state, running near users. It blends PaaS convenience with control over where code runs.
Machines and microVMs
Fly runs your container image inside a Firecracker microVM, giving VM-level isolation with fast startup. These Machines can scale up, down, or to zero, and you place them in the regions you choose for low latency.
Global by default
You can deploy the same app to multiple regions and Fly routes users to the nearest healthy instance via Anycast. This makes a globally low-latency app straightforward without assembling a multi-region setup yourself.
What it supports
- Any app you can put in a container.
- Persistent volumes and managed Postgres for state.
- Private networking between your apps.
When to choose Fly
Fly suits teams that want simple deploys but also geographic distribution and full-stack control, including stateful services. It sits between a managed PaaS and raw cloud, with a strong story for running close to users.
Role in CI/CD
A pipeline builds the image (or lets Fly build it) and deploys with flyctl deploy. GitHub Actions runs the deploy using a Fly API token stored as a secret, typically after tests pass. Fly performs a rolling release across Machines, and you can stage in a separate app first.
Key takeaways
- Fly.io runs containers as Firecracker microVMs in regions near your users.
- Anycast routing makes globally low-latency apps simple to deploy.
- Pipelines deploy with flyctl from GitHub Actions after tests pass.