Subdomain vs custom domain
In a SaaS product, a subdomain is an address the vendor issues under its own domain, such as acme.yourproduct.com; a custom domain is an address on the customer's own domain, such as app.acme.com, which the customer points at the product through their DNS.
Also called: Custom domain, Branded domain, Tenant subdomain
Two ways to give a tenant an address
Most multi-tenant products start with tenant subdomains: acme.yourproduct.com, globex.yourproduct.com. You own the domain, so one wildcard DNS record and one wildcard certificate cover every tenant. The customer does nothing.
A custom domain is the customer's own name, app.acme.com or status.acme.com, pointed at your product. The customer has to change their DNS, you have to obtain a certificate for a name you do not own, and your application has to map an arbitrary hostname to a tenant. In return the customer's page carries their brand end to end.
What changes for each
- DNS. Subdomain: yours, one wildcard record. Custom domain: the customer's DNS host, one CNAME for a subdomain or A records for an apex.
- TLS. Subdomain: one wildcard certificate. Custom domain: a certificate per hostname, issued once the DNS points at you, usually through ACME or a platform such as Cloudflare for SaaS.
- Tenant lookup. Subdomain: parse the first label. Custom domain: look the full Host header up in a table of verified hostnames.
- Cookies. Tenant subdomains share your registrable domain, so a cookie scoped to it reaches every tenant. Custom domains are separate sites, isolated by default.
- Search. Pages on a tenant subdomain build your domain's reputation; pages on a custom domain build the customer's. Customers who care about SEO ask for the latter.
- Ownership. A custom domain needs verification before you serve it, and monitoring afterwards, because the customer can change their DNS at any time.
A subdomain of the customer's domain is still a custom domain
The words overlap. app.acme.com is a subdomain of acme.com, and it is a custom domain from your product's point of view. In custom-domain work the useful split is not subdomain versus domain but subdomain versus apex of the customer's zone: a subdomain can be a CNAME to you, an apex cannot.
Which should a SaaS product offer?
Both, usually: a tenant subdomain on day one so nobody waits on DNS, and a custom domain for customers who want their brand on it. Many products gate custom domains to paid plans. Webflow's free Starter plan, for example, publishes only on a webflow.io subdomain, and Notion charges a monthly add-on per custom domain for Notion Sites. The guide to custom domains and conversion looks at what evidence exists that the feature moves conversion, and how to measure it in your own product.
The hard part of a custom domain is not the code that reads the Host header; it is getting a non-technical customer's DNS changed, verified, and kept that way. The Next.js guide walks through the whole path on one stack.
Related
- Do custom domains raise conversion?
What the evidence says, and how to test it in your own product.
- Custom domains in multi-tenant Next.js (docs)
Tenant lookup, DNS, TLS and the apex on one stack.
- DoDomain with Cloudflare for SaaS
One way to hold certificates for customer hostnames, and where DNS setup fits.
- Apex domain
Why customers who want their bare domain need different records.
Frequently asked questions
What is the difference between a subdomain and a custom domain in SaaS?
A subdomain is an address the vendor issues on its own domain, like acme.yourproduct.com. A custom domain is on the customer's own domain, like app.acme.com, and needs the customer to change their DNS.
Is app.customer.com a subdomain or a custom domain?
Both. It is a subdomain of customer.com and a custom domain from the SaaS product's point of view. Because it is not the apex, the customer can connect it with a single CNAME record.
Does a custom domain help SEO?
It changes whose domain the pages build reputation for. Content on a tenant subdomain accrues to the vendor's domain; content on a custom domain accrues to the customer's.
Do I need a wildcard certificate for custom domains?
No. A wildcard certificate covers tenant subdomains on your own domain. Custom domains need a certificate for each customer hostname, issued once their DNS points at you.