Fly.io

Fly.io is a modern application deployment platform that enables developers to run their applications globally, close to users, using hardware-virtualized containers distributed across a worldwide network of data centers. Unlike traditional PaaS platforms that deploy applications to a fixed region, Fly.io makes it practical to run applications in dozens of locations simultaneously, dramatically reducing latency for globally distributed users.

The core technology behind Fly.io is Firecracker, the lightweight virtual machine technology originally developed by AWS and used in AWS Lambda. Each application container on Fly.io runs inside its own Firecracker microVM, providing the security isolation of a full virtual machine with the startup speed and resource efficiency of a container. This technology choice enables Fly.io to start new instances in milliseconds and support tens of thousands of VMs on a single physical host.

Fly Machines is the underlying compute primitive on Fly.io. A Fly Machine is a Firecracker microVM that can be started, stopped, and scaled independently. Machines can be started in response to incoming requests and stopped when idle, providing a serverless-like scaling behavior where compute costs directly reflect actual usage. Machines are deployed from any Docker image, making the platform compatible with virtually any application stack.

Fly Apps is the higher-level application management abstraction built on Fly Machines. With a fly.toml configuration file and the flyctl CLI, developers can define their application's configuration, environment variables, scaling policies, health checks, and regional deployment preferences. A single fly deploy command builds the application image and deploys it to all configured regions simultaneously.

Fly Postgres is a managed PostgreSQL service built on Fly Machines that provides global read replicas, write forwarding, and automatic primary failover. By deploying read replicas in the same regions as the application, Fly Postgres enables low-latency database reads for users anywhere in the world. LiteFS provides distributed SQLite using Fly Volumes and FUSE-based replication, enabling a lightweight global database architecture.

Private networking on Fly.io uses WireGuard tunnels to create encrypted private networks between all Fly Machines in an organization, regardless of which region they run in. This makes service-to-service communication secure and low-latency across regions without exposing services to the public internet.

Fly.io's geographic footprint spans over 35 regions across North America, South America, Europe, Asia, and Australia. The platform is particularly well-suited for applications where latency to end users is a critical performance requirement, such as real-time applications, gaming backends, API gateways, and AI inference services.