Overview
Fly.io is a cloud platform for deploying and running application servers and short-lived compute close to end users, with fast-starting VMs (“Machines”) that scale out globally. It’s designed for builders who want distributed, low-latency apps and secure sandboxed execution without managing complex infrastructure.
Quick Info
- Category
- Developer Tools
- Pricing
- custom
- Website
- fly.io
Who It's For
Target Audience
Developers and small-to-mid sized engineering teams building globally distributed apps, APIs, and agent/sandbox workloads
Common Use Cases
- Deploying web apps and APIs in multiple regions for sub-100ms user latency
- Running isolated sandboxes to execute untrusted or AI-generated code safely
- Scaling agent-style workloads (background workers, automation, AI agents) up and down on demand
- Hosting stateful services and clustered databases (e.g., Postgres/Cockroach) closer to users
- Spinning up ephemeral per-user/per-task environments (preview apps, per-tenant compute, batch jobs)
Key Features
Fly Machines (fast-starting micro-VMs)
Hardware-virtualized containers that boot quickly and can handle requests on demand. This matters for workloads that need VM isolation but still want near-serverless responsiveness and easy horizontal scaling.
Secure sandboxes (“Sprites”) for untrusted code
Self-contained environments that start in under a second and are designed to run untrusted/AI-generated code with strong isolation. Useful for code execution products, agent runtimes, and multi-tenant compute where safety is critical.
Scale-to-zero and per-second usage billing
Machines can run only when needed, and billing is based on actual CPU/memory consumption down to the second. This reduces cost for spiky, event-driven, or intermittently used services.
Global deployment across regions
Deploy to many regions (e.g., Sydney to São Paulo) to reduce latency for a worldwide user base. Helps deliver a “native-app feel” without building your own multi-region infrastructure.
Storage options: local NVMe + durable object storage
Fast local NVMe supports low-latency workloads, while global durable storage supports data that must persist. This provides flexibility for caching, scratch space, and durable data needs.
Snapshotting and checkpoint/restore for environments
Ability to snapshot or checkpoint an environment and restore it if something breaks. Valuable for reproducible sandboxes, rapid experimentation, and resilient task execution.
Built-in private networking and encryption
Private networks per sandbox with granular routing and end-to-end encryption handled automatically. Reduces operational burden and improves security for distributed systems and internal service communication.
Why Choose Fly
Key Benefits
- Lower end-user latency by deploying compute close to users across multiple regions
- Stronger isolation via per-instance VMs with dedicated CPU, memory, networking, and filesystem
- Faster iteration by launching environments quickly and restoring from snapshots/checkpoints
- Cost efficiency through on-demand execution and per-second resource billing
- Simplified distributed architecture with built-in private networking and automatic encryption
Problems It Solves
- High latency for global users when apps are deployed in a single region
- Operational complexity of running multi-region infrastructure, networking, and scaling
- Need to execute untrusted or AI-generated code without risking the host or other tenants
- Inefficient costs from always-on servers for workloads that are bursty or intermittent
Pricing
Fly.io typically follows usage-based cloud pricing (pay for consumed CPU/memory time, storage, and bandwidth), often with a free or low-cost entry tier for experimentation. Exact rates vary by region and resource type, so expect to estimate costs based on workload patterns.
Free/Developer
Intended for learning and small experiments; limited included resources and/or credits (availability and limits may vary).
Pay-as-you-go
PopularPer-second billing for compute plus charges for storage and network usage; suitable for production apps with variable demand.
Enterprise
For larger organizations needing higher limits, procurement support, and potentially enhanced support/SLA options.
Pros & Cons
Advantages
- Strong isolation model (micro-VMs) that’s well-suited to multi-tenant and untrusted-code workloads
- Global, multi-region deployment designed to reduce latency without heavy infrastructure work
- Fast startup and on-demand execution can cut costs for spiky workloads
- Built-in private networking and encryption reduces networking/security setup complexity
- Good fit for distributed systems patterns and modern agent/worker architectures
Limitations
- Not as “fully managed” as some PaaS offerings; teams may still need to understand deployment, networking, and state management concepts
- Multi-region stateful systems (databases, storage consistency) can be complex and may require careful architecture choices
- Costs can become harder to predict for high-traffic or always-on workloads without careful monitoring and sizing
Alternatives
AWS offers the broadest ecosystem and deep enterprise capabilities, but typically requires more configuration and operational expertise. Choose AWS if you need extensive managed services and compliance options; choose Fly.io if you want simpler global app placement and fast-starting VM isolation for app/sandbox workloads.
Cloud Run is excellent for containerized HTTP services with strong autoscaling and a serverless experience, but it’s more opinionated and less focused on per-instance VM isolation for untrusted code. Choose Cloud Run for straightforward stateless services; choose Fly.io for VM-level isolation and distributed systems patterns.
Render provides a more traditional PaaS experience with simpler workflows for many web apps, but may offer less flexibility for advanced multi-region and sandbox-style compute. Choose Render for ease-of-use and standard web services; choose Fly.io for low-level control, isolation, and distributed compute close to users.
Getting Started
Identify your workload type (web app/API, background workers, sandboxed execution) and decide whether it needs multiple regions and/or persistent storage.
Create an account on Fly.io and install the Fly CLI; authenticate and initialize a new app from your project repository.
Deploy your first Machine, then configure regions, autoscaling behavior (including scale-to-zero if appropriate), and private networking between services.
Add storage as needed (local volumes/NVMe use cases vs durable storage), set up monitoring/cost alerts, and run a load test to validate latency and scaling.
The Bottom Line
Fly.io is a strong choice for developers who want globally distributed compute with fast-starting micro-VM isolation, especially for agent runtimes, sandboxed code execution, and low-latency apps. Teams that prefer a highly opinionated, fully managed PaaS or that need extensive managed service integrations may find alternatives like Cloud Run, Render, or a full AWS stack a better fit.