Supporting driver versioning is problematic; our current approach does not adequately solve the problem and creates a maintenance burden with minimal justification for this technical debt.
Fake out implementation is problematic. When we create a wrapper to support a legacy driver, we attempt to “fake out” any new methods, so that they don’t fail or cause an error. This can be easy enough for simple drivers, but considerably more difficult for complicated implementations, to the point where we have to change the implementation in order to support the legacy driver. Or, when that is not possible, resort to raise exception.NotImplemented(). This is problematic and can lead to unforeseen bugs caused from the “faked out” code and custom implementation.
Maintainability. By supporting legacy drivers, we are forced to maintain the legacy driver code, wrappers, as well creating our own custom drivers in order to thoroughly test that the older version can successfully pass all tests. So we have V8 underscore and all of these other dependent objects littered throughout the code base that has to be maintained and cleaned up for every release. And this is no small feat. For example, the patch for creating a V9 driver for only identity, has over 600 lines: https://review.openstack.org/#/c/305315/
Minimal justification. We only support driver versions for one version back, which means deployers will have to upgrade their current custom drivers soon anyway. And realistically, how many operators are upgrading to the latest version without upgrading and testing their custom drivers?
In addition, I sent an email to the operators mailing list regarding this. I did not receive any feedback from operators that they were utilizing driver versioning; nor that dropping support would negatively impact them.
When a driver contract changes, we clearly document it in the release notes and documentation. Thus, in order for clients to upgrade, they will need to: 1. Upgrade their custom drivers to meet the new driver contracts. 2. Thoroughly test their custom drivers against the new code base.
For Newton, we would document this change and remove support for legacy drivers in Ocata.
Continue with current approach or find a new approach to better support legacy drivers.
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Custom drivers would need to meet driver contracts when upgrading.
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Minimal documentation changes will be needed; mostly just removing text.