RPCVersionCapError: Requested message version, 3.0 is incompatible. It needs to be equal in major version and less than or equal in minor version as the specified version cap 2.0.

[jun923.gu]

We encounter the above problem when upgrading from mitaka to pike. Because the error cause openstack-cinder-scheduler service can't run. I had analyzed the problem deeply and found that the cinder.services.rpc_current_version is incompatible on the mysql for cinder-volume. That is to say, the cinder.services.rpc_current_version is 2.7 for mitaka. and the value is 3.15 for pike. So this cause the exception raise.
So I wish someone can confirm whether this problem is a bug or not. Thanks!

[Sean McGinnis (sean-mcginnis)]

Looks like the upgrades to Newton and Ocata might not have completed. Make sure to complete each step before moving on to the next.

Make sure to follow all steps in the upgrade process described here:

https://docs.openstack.org/cinder/latest/upgrade.html

[jun923.gu (gujun1989)]

I upgrade OpenStack from Mitaka to Pike directly. After upgrading to Pike, The cinder-volume service will report new service information to cinder.services table. The new service information for Pike is different from the old service information for Mitaka(the cinder.serivices.host is different).
For example:
Mitaka:
The cinder.services.host was host123
Pike:
The cinder.services.host would be host123@<cinder_driver_name>
So the old services information for Mitaka still existed on the cinder.serices and the cinder.services.rpc_current_version is 2.7. When startup cinder-scheduler service, it will call cast function to cinder-volume. The oslo.messaging will check the rpc_current_version and find the rpc_current_version of old services is different from new rpc_current_version. The exception will be raised.

[Xav Paice (xavpaice)]

This is likely to be that there's some services in the cinder db services table that need to be removed, which is blocking the start of the service. The upgrade doc mentioned in #1 has instructions to remove them - you can see them with 'cinder service-list'.