[openstack-dev] [oslo.messaging][zeromq] Next step
Alec Hothan (ahothan)
ahothan at cisco.com
Tue Jun 16 19:51:30 UTC 2015
These are all great points for RPC messages (also called "CALL" in oslo
messaging). There are similar ambiguous contracts for the other types of
messages (CAST and FANOUT).
I am worried about the general lack of interest from the community to fix
this as it looks like most people assume that oslo messaging is good
enough (with rabbitMQ) and hence there is no need to invest any time on an
alternative transport (not mentioning that people generally prefer to work
on newer trending areas in OpenStack than contribute on a lower-level
I saw Sean Dague mention in another email that RabbitMQ is used by 95% of
OpenStack users - and therefore does it make sense to invest in ZMQ (legit
question). RabbitMQ had had a lot of issues but there has been several
commits fixing some of the issues, so it would make sense IMHO to make
another status update to reevaluate the situation.
For OpenStack to be really production grade at scale, there is a need for
a very strong messaging layer and this cannot be achieved with such a
loose API definitions (regardless of what transport is used). This will be
what distinguishes a great cloud OS platform from a so-so one.
There is also a need for defining more clearly the roadmap for oslo
messaging because it is far from over. I see a need for clarifying the
- validation at scale and HA
- security and encryption on the control plane
On 6/16/15, 11:25 AM, "Gordon Sim" <gsim at redhat.com> wrote:
>On 06/12/2015 09:41 PM, Alec Hothan (ahothan) wrote:
>> One long standing issue I can see is the fact that the oslo messaging
>> documentation is sorely lacking details on critical areas such as API
>> behavior during fault conditions, load conditions and scale conditions.
>I very much agree, particularly on the contract/expectations in the face
>of different failure conditions. Even for those who are critical of the
>pluggability of oslo.messaging, greater clarity here would be of benefit.
>As I understand it, the intention is that RPC calls are invoked on a
>server at-most-once, meaning that in the event of any failure, the call
>will only be retried by the olso.messaging layer if it believes it can
>ensure the invocation is not made twice.
>If that is correct, stating so explicitly and prominently would be
>worthwhile. The expectation for services using the API would then be to
>decide on any retry themselves. An idempotent call could retry for a
>configured number of attempts perhaps. A non-idempotent call might be
>able to check the result via some other call and decide based on that
>whether to retry. Giving up would then be a last resort. This would help
>increase robustness of the system overall.
>Again if the assumption of at-most-once is correct, and explicitly
>stated, the design of the code can be reviewed to ensure it logically
>meets that guarantee and of course it can also be explicitly tested for
>in stress tests at the oslo.messaging level, ensuring there are no
>unintended duplicate invocations. An explicit contract also allows
>different approaches to be assessed and compared.
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