I've recently learned about DNS supporting SRV records, which identify what port, and what protocol should be used for a given service. For example _http._tcp.example.com SRV should return a port, and an A/AAAA record where the client should be opening a connection which intends to access HTTP service on example.com using TCP.
How widely is this supported? What handles checking that the service is expected to be present on a given domain: The OS (network stack) or the Application? As far as I remember, whenever opening a socket, I would never specify anything more than whether it's a TCP socket or UDP socket. Would any given client respect if I were to set an SRV record _https._tcp.example.com to 0 1 444 example.com which would mean that it should be using port 444 for https connections over tcp?
Best Answer
SRV records have been supported by DNS server and client implementations for over 23 years.
What does not commonly support SRV records are applications. The most common application that uses SRV records is Microsoft Active Directory LDAP/Authentication. Aside from SIP records, SRV support by other applications is comparatively low.
Note that any application can consume and use SRV records. The cost for implementation is negligible. The fact that SRV record usage by applications is low indicates low demand. Usually due to the overhead/latency in the lookup.