Fly Apps support custom domains via fly certs add. The proxy terminates TLS, Let’s Encrypt
certificates are provisioned automatically, and DNS setup is straightforward (CNAME or
A/AAAA records). It works well.
Sprites don’t have this. The current workarounds all involve third-party proxies
(Cloudflare, Vercel, Caddy on a VPS, etc.) to terminate TLS for the custom domain and
forward to the *.sprites.app URL. These add latency, complexity, and an external dependency
for what is fundamentally a solved problem — Fly.io already has the infrastructure for
this on the same platform.
The request: Port the existing Fly Apps custom domain system to Sprites. Something like:
sprite url update --domain mcp.example.com
which would:
- Register the hostname with Fly Proxy (via Corrosion, as it already does for
*.sprites.app) - Provision a Let’s Encrypt certificate (same flow as
fly certs add) - Instruct the user to set a CNAME or A/AAAA record
From the user’s perspective, the only difference between a Fly App and a Sprite is that a
Sprite has a persistent filesystem while a Fly App rebuilds from an image. The networking
and proxy layer shouldn’t need to differ.