Overview

Fly.io takes a fundamentally different approach to deployment: instead of serverless functions or traditional servers in a single region, Fly runs your applications as micro-VMs distributed globally. Your code runs in 30+ regions simultaneously, responding to users from the nearest location with true server capabilities, not just edge functions.

This architecture enables use cases that serverless platforms struggle with: globally distributed databases, websocket connections, stateful applications, and latency-sensitive workloads. If you need your application to truly run everywhere, not just cache everywhere, Fly delivers.

The trade-off is complexity. Fly's model requires more understanding of distributed systems than pushing to Vercel. The CLI is powerful but assumes technical proficiency. For teams with the expertise, Fly offers capabilities that other platforms can't match.

Features Deep-Dive

Global Anycast Deployment

Fly's anycast networking routes requests to the nearest running instance automatically. Deploy to multiple regions with a single command, and users connect to whichever instance is closest. Failover is automatic, if one region goes down, traffic shifts seamlessly.

This isn't CDN caching; it's your actual application running in multiple locations simultaneously.

Persistent Volumes

Unlike serverless platforms limited to ephemeral storage, Fly supports persistent volumes attached to VMs. Run databases, store uploads, or maintain state across restarts. Volumes replicate across availability zones for durability.

This enables architectures that serverless functions simply can't support.

Fly Postgres

Fly offers managed Postgres with automatic replication across regions. Read replicas distribute globally, serving queries from the nearest location. Primary databases handle writes, with replication keeping replicas current.

For applications needing low-latency database access worldwide, Fly Postgres provides capabilities that centralized databases can't match.

Pricing Analysis

Fly's free tier includes 3 shared-CPU VMs, 3GB persistent storage, and 160GB outbound transfer monthly. This is enough to run small applications across multiple regions at no cost.

Beyond free allowances, pricing is usage-based: $0.0000022 per second for shared CPUs, with dedicated CPUs and additional memory priced accordingly. Bandwidth is $0.02/GB after free allowances.

The pricing model favors always-on applications distributed globally. For sporadic workloads, serverless platforms may be more economical. For consistently running global applications, Fly offers competitive value.

Who Is This For?

Fly.io works best for:

• Globally distributed applications needing true multi-region presence
• Latency-sensitive workloads where milliseconds matter
• Stateful applications requiring persistent storage
• Teams with DevOps capability comfortable with complexity
• Real-time applications using websockets or long-polling

Who Should NOT Use This

Fly.io might not be the right choice if:

• Simplicity is priority: Vercel and Netlify are easier
• Serverless fits perfectly: Edge functions may be simpler
• Frontend-only projects: Overkill for static sites
• Limited DevOps expertise: Learning curve is steeper
• Sporadic traffic: Usage-based pricing may not favor you

Bottom Line

Fly.io offers unique capabilities for globally distributed applications. If your use case requires running servers, not just functions, in multiple regions with low latency, Fly provides what alternatives can't. The architecture enables distributed databases, websocket servers, and stateful applications at global scale.

The complexity is real. Teams need distributed systems understanding to use Fly effectively. For those with the expertise, the platform unlocks architectures that other platforms fundamentally can't support.

FAQ

How does Fly.io differ from Vercel Edge Functions?

Vercel Edge Functions run stateless code at the CDN edge with limited runtime. Fly runs full VMs with persistent storage, databases, and long-running processes. Use Vercel for request-time logic, Fly for distributed applications.

Is Fly.io difficult to learn?

Fly requires more technical knowledge than Vercel or Netlify. The CLI assumes familiarity with Docker, networking, and distributed systems. Documentation is excellent but expects proficiency.

Can I run databases on Fly?

Yes. Fly Postgres provides managed, globally distributed databases. You can also run other databases in Fly VMs with persistent volumes. This is a key differentiator from serverless platforms.

How does Fly pricing compare to alternatives?

Fly's usage-based model is competitive for always-on global applications. For sporadic traffic or single-region deployments, simpler platforms may cost less. Model your specific workload to compare.

Is Fly suitable for production?

Yes. Many production applications run on Fly, including latency-sensitive and globally distributed workloads. The platform provides monitoring, logging, and reliability features for production use.