Fly.io alternative for SaaS custom domains
An evidence-based comparison of Fly.io and subdomain.to for connecting customer-owned domains, managing certificates and routing HTTPS traffic.
Reviewed · Sources checked against first-party documentation
Is subdomain.to a good Fly.io alternative?
Yes, when the job is specifically to connect customer-owned domains to an existing SaaS application. Fly.io is the better fit when the application is deployed on Fly Machines and the team wants Fly Proxy, IP allocation and certificates in one environment. subdomain.to is the alternative when the origin lives elsewhere and product teams want managed DNS checks, routing states, webhooks and onboarding without operating certificate resources through the hosting platform. Fly.io attaches domains and ACME certificates to Fly Apps. It supports A/AAAA, CNAME, DNS-01 and ownership TXT verification patterns, exposes certificate resources through an API and forwards hostname context that applications can use for tenant resolution.
The products are not identical. This page compares only the overlapping custom-domain job; it does not score unrelated hosting, CDN, registrar or infrastructure features as if they were interchangeable.
Fly.io vs subdomain.to
“Different” is not automatically worse. The right choice depends on whether you need a broader platform, direct infrastructure control or a focused custom-domain layer.
Product and pricing information reviewed July 30, 2026. Confirm current contractual terms with each vendor before purchasing.
Fly.io in three verifiable facts
The comparison uses public, first-party material rather than review-site scores or inferred capabilities.
Managed CA
Let’s Encrypt
Domain resource
Certificate attached to a Fly App
Validation choices
TLS-ALPN, HTTP-01, DNS-01 or ownership TXT
Compare the cost boundary, not one headline number.
Fly.io pricing is driven by Machines, networking, storage and selected IP resources rather than a standalone custom-domain subscription.
For a fair total-cost comparison, include implementation time, bandwidth or compute, certificate recovery, monitoring, support tooling and the cost of changing providers later. See the build-versus-buy model.
Where Fly.io is strong
Fly.io attaches domains and ACME certificates to Fly Apps. It supports A/AAAA, CNAME, DNS-01 and ownership TXT verification patterns, exposes certificate resources through an API and forwards hostname context that applications can use for tenant resolution.
- Global application deployment and proxy routing in one platform.
- Multiple certificate validation and DNS configuration options.
- Certificate API supports managed and imported certificates.
- IPv4, IPv6, wildcard and custom-certificate flexibility.
What your team still owns
These are scope differences to evaluate, not claims that the competitor is unsuitable.
- 01The direct custom-domain workflow is centered on a Fly App.
- 02Your team handles Fly resources, IP choices and certificate troubleshooting.
- 03Let’s Encrypt rate limits and DNS-provider interactions remain visible operational concerns.
Choose from your operating constraints
A useful comparison names the conditions under which either product wins.
Choose Fly.io when…
- Your application already runs globally on Fly Machines.
- IPv6, imported certificates or wildcard certificates are required.
- Your infrastructure team wants direct proxy and certificate control.
Choose subdomain.to when…
- The application runs outside Fly.io.
- Support needs clear DNS, certificate and routing status fields.
- You want certificate and routing operations hidden behind a product API.
Moving from Fly.io without a DNS cliff
Run both paths during the transition. A domain move combines DNS propagation, certificate readiness and application routing; deleting the old route first removes your safest rollback.
- 01
Inventory
Export the Fly App, hostname, certificate status, IP and DNS-requirement mapping.
- 02
Prepare
Confirm that the target application accepts traffic from subdomain.to and resolves tenants using forwarded hostname context.
- 03
Cut over
Activate domains before removing Fly certificates or IPs; keep a rollback DNS value through the propagation window.
How this comparison was produced
subdomain.to publishes this page and is therefore not a neutral review marketplace. We compare the shared customer-domain workflow, acknowledge where Fly.io is stronger, cite first-party product documentation and avoid ratings we did not collect. subdomain.to claims are checked against the implemented application and public pricing page.
We review pricing, scope and source links quarterly or after a material product announcement. If a public fact cannot be verified, it is described as plan-dependent or omitted. Send corrections to hello@subdomain.to.
Fly.io alternative FAQ
Short answers for engineering, product and procurement teams.
Can Fly.io manage certificates through an API?
Yes. Fly documents API resources for requesting ACME certificates, checking status, deleting them and importing custom certificates.
Does subdomain.to support custom certificate uploads?
The public product offer describes a managed certificate workflow, not customer certificate import. Choose Fly.io when certificate import is required.
Can either service identify the tenant for my app?
They can preserve hostname context, but your application must map that hostname to the correct tenant and perform authorization.
How current is this comparison?
It was last reviewed on July 30, 2026 against the official product and documentation links above. Vendor plans and features can change, so verify contractual details before purchase.