On 05/02, Paul Browne wrote:
Hi list,
I had a quick question about Active-Active in cinder-volume and cinder-backup stable/stein and RBD driver, if anyone can help.
Using only the Ceph RBD driver for volume backends, is it required to run A-A cinder services with clustering configuration so that they form a cluster?
And, if so, is an external coordinator (redis/etcd/Consul) necessary, again only using RBD driver?
Hi, For the time being the cluster concept only applies to the cinder-volume service. The cinder-backup service has 2 modes of operation: only backup from current node (so we can have different backup drivers on each node) deployed as A/P, and backup from any node (then all drivers must be the same) deployed as A/A. When deploying cinder-volume as active-active a coordinator is required to perform the functions of a DLM to respect mutual exclusion sections across the whole cluster. Drivers that can be used for the coordination are those available in Tooz [1] that support locks (afaik they all support them). If you don't form a cluster and deploy all cinder-volume services in A/A sharing the same host you'll end up in a world of pain, among other things, as soon as you add a new node or a cinder-volume service is restarted, as it will disturb all ongoing operations from the other cinder-volume services. I hope this helps. Cheers, Gorka. [1]: https://docs.openstack.org/tooz/latest/user/drivers.html
Best docs I could find on this so far were;
https://docs.openstack.org/cinder/latest/contributor/high_availability.html ,
I support more aimed at devs/contributoers than operators, but it's not 100% clear to me on these questions
Thanks, Paul
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