Why do browsers not use SRV records?

Question

Why do browsers not use SRV records?

It seems like a minimal amount of work and it will make the server-side implementation of reliable websites much simpler.

For example, you can specify tiers, such that www.example.com resolves to 1.2.3.4 and 2.3.4.5, and only if neither of those are available, try 4.5.6.7.

SRV records have been around for years...

Is there something I'm missing here?

Answer 1

The RFC for SRV records specifies that it may not be used by pre-existing protocols which did not already specify the use of SRV records in their specifications. I.e. no SRV in the HTTP spec - browsers are, by the SRV standard, prohibited from using it.

This does not prohibit a new HTTP 1.2 standard from specifying the use of SRV records, though. However, Mark Andrews proposed this in April 2007 to the IETF HTTP working group, but got no response.

Answer 2

There have been two efforts to introduce this that I know of:

1. draft-andrews-http-srv (2002)

2. draft-jennings-http-srv (2009)

The "Open Issues" paragraph of the latter draft is illuminating:

The big open issue seems to be if one should just update the HTTP scheme to do this SRV lookup and not create a new scheme.  The 00 version of this draft did that.  A new scheme makes this somewhat unusable for general web surfing while using the old scheme results in a very long transition times where different clients resolve URLs in different ways. 

and that is the crux of the matter. If your site relies on SRV records to be found, it won't work for some users until every browser supports it.

Would you take that risk, without some sort of transition mechanism?