At yesterday's Trove team meeting [1] there was significant discussion around the Capabilities [2] feature. While the community previously approved a BP and some of the initial implementation, it is apparent now that there is no agreement in the community around the requirements, use cases or proposed implementation.
I mentioned in the meeting that I thought it would make sense to adjust the current BP and spec to reflect the concerns and hopefully come up with something that we can get consensus on. Ahead of this, I thought it would to try to write up some of the key points and get some feedback here before updating the spec. First, here are what I think the goals of the Capabilities feature are: 1. Provide other components with a mechanism for understanding which aspects of Trove are currently available and/or in use 2. Allow operators the ability to control some aspects of Trove at deployment time Use Cases 1. Unimplemented feature - this is the case where one/some datastore managers provide support for some specific capability but others don't. A good example would be replication support as we are only planning to support the MySQL manager in the first version. As other datastore managers gain support for the capability, these would be enabled. 2. Unsupported feature - similar to #1 except this would be the case where the datastore manager inherently doesn't support the capability. For example, Redis doesn't have support for volumes. 3. Operator controllable feature - this would be a capability that can be controlled at deployment time at the option of the operator. For example, whether to provide access to the root user on instance creation. 4. Downstream capabilities addition - basically the ability to use capabilities as an extension point. Allow downstream implementations to add capabilities that aren't present in upstream Trove. Requirements 1. There are a well known set of capabilities that are provided with upstream Trove. Each capability is either read-only (basically use cases 1 & 2) or read-write (use case 3). Use case #4 capabilities are not part of the "well known" set. 2. Each capability can be over-ridden at the datastore manager level, the datastore level or the datastore version level. The datastore manager level would be used for the read only capabilities and specified by a given version of Trove. Datastore/Datastore version overrides would be for Operator controllable capabilities that are read-write. 3. The datastore/datastore version overrides are only present if created by the Operator at deployment time. 4. A clean Trove install should create the domain of known capabilities and the datastore manager overrides relevant to the installed version of Trove. 5. Upgrades - need to provide a mechanism to migrate from a version of Trove where: a. A capability is being moved from historical config file into the capability mechanism b. A previously non-existent capability is being introduced. c. Capability adjustments have occurred in the newer version that affect the datastore manager level capabilities. This likely has some impact on old-version guest agents running against capability upgrades. Any feedback is welcome. Hopefully, based on the feedback we can update the spec and move forward on adjusting the implementation. Regards, Doug [1] http://eavesdrop.openstack.org/irclogs/%23openstack-meeting-alt/%23openstack-meeting-alt.2014-07-02.log starting at 18:05 [2] https://wiki.openstack.org/wiki/Trove/trove-capabilities
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