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Application platform

Fly.io

Fly.io, Inc. · Application platform. How DNSTrace.dev identifies it from public evidence.

Updated Sep 2026

What Fly.io is

Fly.io runs containerised applications as virtual machines placed in specific regions, with an anycast proxy in front that routes each request to the nearest running instance. Because the proxy and the application host are the same platform, a Fly.io response identifies both the delivery edge and where the application itself is running.

How DNSTrace.dev detects it

Detection correlates independent public signals. A single match is reported as strong evidence; agreement between a response header and the announcing network is reported as confirmed.

  • fly-request-id — Per-request identifier appended by the Fly proxy.
  • fly-region — The three-letter code of the region that handled the request.
  • CNAME targets under fly.dev — The default application hostname before a custom domain is attached.
  • Shared anycast A and AAAA records — Fly issues anycast addresses that several applications can share, so an address alone does not isolate one app.

What a detection proves

The request was routed by the Fly.io proxy, and the named region served it.

What it does not prove

Which application or organisation owns the instance, or whether the application also runs in other regions that did not answer this request.

Common questions

What does fly-region tell me?

It names the Fly.io region that served this specific request. A different region may answer the same hostname from another part of the world.

Can two sites share a Fly.io address?

Yes. Fly anycast addresses are shared, so reverse lookups and address matching cannot attribute an address to a single application.

Compare with

Frontend application platformVercel

Vercel, Inc.

Frontend application platformNetlify

Netlify, Inc.

Application platformHeroku

Salesforce, Inc.

CDN, reverse proxy and WAFCloudflare

Cloudflare, Inc.

Check a domain

Run a full lookup to see the delivery layer, the detected application stack, live TLS and the announcing network side by side.

Check response headers Read the DNS records

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