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  1. OpenShift Storage
  2. STOR-1281

Make Cinder CSI Driver Topology feature configurable


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      Currently, the Topology Feature is enabled by default by the openstack-cinder-csi-driver-operator. As seen in OCPBUGS-4697, this is problematic in environments where there is a mismatch between Nova and Cinder AZs, such as in DCN environments where there may be multiple nova AZs but only a single cinder AZ. On initial read, the [BlockStorage] ignore-volume-az would appear to offer a way out, but as I noted in OCPBUGS-4697 and upstream, this doesn't actually do what you'd think it does.

      We should allow the user to configure this functionality via an operator-level configurable. We may wish to go one step further and also attempt to auto-detect the correct value by inspecting the available Nova and Cinder AZs. The latter step would require OpenStack API access from the operator, but both services do provide non-admin APIs to retrieve this information.

      We also explored other options:

      • Make the AZ reported by the CSI node configurable by the user/operator, like the Manila CSI driver appears to do via a --nodeaz flag. This would require upstream changes and wouldn't actually address the scenario where Nova and Cinder AZs are distinct sets: an AZ that was valid for Cinder would allow us to create the volume in Cinder, but it would still be applied to the resulting PV as a nodeAffinity field unless you also set ignore-volume-az. This would conflict with the Nova-based AZs assigned to Nodes and prevent scheduling of the PV to any Node.
      • Change the meaning of [BlockStorage] ignore-volume-az to also avoid sending AZ information to Cinder, causing Cinder to fallback to [DEFAULT] default_availability_zone. This would also require upstream changes and would effectively give users two ways to disable the Topology feature. This would increase confusion and result in a worse UX.

            sfinucan@redhat.com Stephen Finucane
            sfinucan@redhat.com Stephen Finucane
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