alternative service probability parameter

Hello httpbis,

This is a heads up about a parameter that we have been using in
Alternate-Protocol headers, and are planning to use in Alt-Svc headers
and ALTSVC frames.  It is "p=" (probability), that Google servers emit
and Chrome observes.  This takes a numerical value between 0.0 and 1.0
inclusive, and tells the client to only observe the alternative
service with that given probability (and ignore it otherwise).  This
parameter can be used for finer grade load balancing, for gradual
rollout of a new protocol, and for performance testing.

My understanding is that the current HTTP Alternative Services draft
permits parameters other than "ma=", therefore using a customary
parameter is conformant to the specification.

If there is interest in more technical documentation of this
parameter, I would be happy to coordinate efforts of writing that
documentation on our part.  Given that according to my best
understanding, the Alternative Services specification is not in Last
Call yet, there is the possibility of including the probability
parameter in that document in case there is a benefit to the
community.  In case of lack of interest, this was just an FYI.

Thank you,


Received on Friday, 8 May 2015 13:38:08 UTC