SadiJr commented on pull request #5901:
URL: https://github.com/apache/cloudstack/pull/5901#issuecomment-1032953373
@DaanHoogland a more complex explanation:
1. To work with volumes, ACS has a listener, called `VolumeStateListener`.
This listener has a method called `postStateTransitionEvent`, which can
generate a Usage Event in some transactional events. The transactional events
that can generate Usage Events can be found in `com.cloud.storage.Volume` class.
2. When creating a new volume (not attached to any VM), the API createVolume
is used. This API call method `allocVolume` of class `VolumeApiServiceImpl`
(which only alloc the volume in DB, without sending the createvolume cmd to
hypervisor, this command is only sended when the volume is attached to a VM),
and, this method calls the method `commitVolume`, which generates a
VOLUME.CREATE Usage Event.
3. So, when destroying a volume in `allocated` state, via API destroyVolume,
the method `destroyVolumeIfPossible` of class `VolumeApiServiceImpl` will be
called and, if the volume state isn't in the Set of volume states cannot be
destroyed (which isn't the case of `allocated` state), the method
`destroyVolume` of class `VolumeServiceImpl` is called.
4. In this method, the volume state has changed to `DestroyRequested` (and
then to `Destroy`) and then to `OperationSucceeded`.
4. When volume changes is state to `Destroy` with `OperationSucceeded`
event, the listener, in the `postStateTransitionEvent` method, generates a
VOLUME.DELETE Usage event.
5. But, in the normal execution, volumes in allocated state has only it
state changed to `DestroyRequested`, but no state change event of type
`OperationSucceeded` is used, which causes ACS, more specific the listener, to
not generate a DELETE Usage Event.
6. To fix this, there a lot of possibilities:
- Don't generate a CREATE Usage Event if volume is not allocated to any
VM;
- Remove the `allocated` state from `STATES_VOLUME_CANNOT_BE_DESTROYED`
Set;
- In the `destroyVolume` method, when volume is in `allocated` state,
make a transaction to `DestroyRequested` and, with success, make another
transaction to `OperationSucceeded`, to make listener generates a DELETE Usage
Event.
7. In this PR, I first used the second option, but, after a new review, I
chose to use the third
PS: I'm not sure I was clear in my answer. If you have any questions or
suggestions, just let me know :)
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