[openstack-dev] [OpenStack-dev][Blueprints][version-rpc-messages][amqp-rpc-fast-reply-queue]Proposal to recover from version mismatch

Ray Pekowski pekowski at gmail.com
Fri Jan 25 04:00:37 UTC 2013

Regarding blueprint
I have some thoughts on enhancing it for a backward compatibility problem
people are having with blueprint

Here is what I propose and I mention in the code review notes:

"Perhaps another Grizzly blueprint could be written to augment Russel
Bryant's version-rpc-messages envelope idea to enabled it by default. Today
it is disabled with a TODO to enable it after Grizzly. Along with this make
the necessary changes to detect an RPC failure caused by New->Old versions
and reissue the RPC without the envelope. Then make my blueprint dependent
upon that one.

And (optionally) perhaps even make a change in the checking of the envelope
to look for unexpected content in that envelope. For example, if we decide
in the future to add an implementation version or whatever, that a version
that supported the envelope, but not the new content would fail the RPC."

What do you think?  Does it have problems?

I see an advantage.  Not only would it work for G  to (<G) versions.  It
would also work for (>G) to (<G) versions.  blueprint version-rpc-messages
interoperability with (<G) after Grizzly.  Maybe that isn't a valid
concern, but one worth mentioning.

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