Glossary

The DNS terms behind custom domains

Connecting a customer's domain to a SaaS product touches a handful of DNS ideas that are easy to half-know. Each entry below explains one of them: what it is, what the rules actually say, and what it means for a product that serves customer domains.

• Apex domain

  An apex domain is the name at the top of a DNS zone, such as example.com with no label in front of it. It is also called the zone apex, root domain, naked domain or bare domain.

• CNAME record

  A CNAME (canonical name) record makes one DNS name an alias of another: a resolver that asks for the alias is told the canonical name and continues its lookup there.

• A record

  An A record maps a DNS name to an IPv4 address. Its IPv6 counterpart is the AAAA record. Together they are the records that finally turn a name into somewhere a connection can go.

• ALIAS record and CNAME flattening

  ALIAS, ANAME and CNAME flattening are DNS-provider features that let a zone apex point at a hostname: the provider's nameservers resolve the target themselves and answer the apex query with ordinary A and AAAA records.

• TXT record verification

  TXT record verification proves control of a domain by asking its owner to publish a specific random value in a DNS TXT record, which the verifying service then reads back from the domain's authoritative nameservers.

• DNS propagation

  DNS propagation is the everyday name for the delay between changing a DNS record and every resolver returning the new value. Nothing is pushed anywhere: the delay is caches expiring at the end of the record's TTL.

• Registrar vs authoritative DNS host

  The registrar is the company a domain is registered and renewed through; the authoritative DNS host is whoever runs the nameservers the domain is delegated to, which is where its records actually live. They are often, but not always, the same company.

• 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.

• Domain Connect

  Domain Connect is an open protocol that lets a DNS provider apply a pre-registered template of DNS records to a user's domain after the user approves a single consent screen at the provider, with no manual record entry.