Scalability of App Platform when mapping thousands of custom domains (SaaS scenario)

Hi everyone — I’m building a SaaS on the DigitalOcean App Platform where each customer has a sub‑domain like user.myplatform.com. I also want to allow customers to bring their own custom domains (e.g. theirbrand.com) and map them to their sub‑domain on our platform (user.myplatform.com).

My questions:

1. If I have thousands of custom domains mapped to a single app instance on App Platform, how scalable is this setup? Are there known limits or performance/handoff issues when you have large numbers of custom domains on one app?

   • For example: Does App Platform impose a limit on “number of custom domains” per app (beyond the documented container/instance limits) when increasing the app spec?

   • Are there operational challenges (certificate issuance delays, DNS propagation, SSL renewal, routing, caching) when adding large numbers of domains programmatically?

   • If many domains point to the same app, does that create any bottlenecks or constraints (e.g., on the CDN, edge routing, certificate management)?

2. Is there a better alternative or pattern for a SaaS like this (many domains per customer) on DigitalOcean? For example:

   • Is there a separate “domain mapping” layer (e.g., using a load balancer, wildcard domain, reverse proxy) that works more smoothly for thousands of domains?

   • Any recommended best practices by DO for custom domain mapping at SaaS scale?

3. Regarding DNS/CNAME from the customer side:

   • Will customers be able to set up a CNAME pointing their custom domain (e.g. theirbrand.com or www.theirbrand.com) to user.myplatform.com (or the .ondigitalocean.app domain) and then we (on our end) add the custom domain via App Platform’s domain settings?