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Reduce volume controller sync period
fixes#24236 and most probably also fixes#25294.
Needs #25881! With the cache, binder is not affected by sync period. Without the cache, binding of 1000 PVCs takes more than 5 minutes (instead of ~70 seconds).
15 seconds were chosen by fair 2d10 roll :-)
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volume controller: Add cache with the latest version of PVs and PVCs
When the controller binds a PV to PVC, it saves both objects to etcd. However, there is still an old version of these objects in the controller Informer cache. So, when a new PVC comes, the PV is still seen as available and may get bound to the new PVC. This will be blocked by etcd, still, it creates unnecessary traffic that slows everything down.
To make everything worse, when periodic sync with the old PVC is performed, this PVC is seen by the controller as Pending (while it's already Bound on etcd) and will be bound to a different PV. Writing to this PV won't be blocked by etcd, only subsequent write of the PVC fails. So, the controller will need to roll back the PV in another transaction(s). The controller can keep itself pretty busy this way.
Also, we save bound PVs (and PVCs) as two transactions - we save say PV.Spec first and then .Status. The controller gets "PV.Spec updated" event from etcd and tries to fix the Status, as it seems to the controller it's outdated. This write again fails - there already is a correct version in etcd.
As we can't influence the Informer cache, it is read-only to the controller, this patch introduces second cache in the controller, which holds latest and greatest version on PVs and PVCs to prevent these useless writes to etcd . It gets updated with events from etcd *and* after etcd confirms successful save of PV/PVC modified by the controller.
The cache stores only *pointers* to PVs/PVCs, so in ideal case it shares the actual object data with the informer cache. They will diverge only for a short time when the controller modifies something and the informer cache did not get update events yet.
@kubernetes/sig-storage
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volume controller: use better operation names
Using volume/claim.UID in the operation name is not really useful, as UIDs are not logged by rest of the controller. On the other hand, volume.Name and claim.Namespace/Name is logged pretty often and it would help to log these also in operation name. Still, I'd prefer to have the operation name really unique to be protected from users deleting a volume and quickly creating another one with the same name, so UID is still part of the operation name.
This has been already proven to be very useful in controller debugging.
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volume recycler: Don't start a new recycler pod if one already exists.
Recycling is a long duration process and when the recycler controller is restarted in the meantime, it should not start a new recycler pod if there is one already running.
This means that the recycler pod must have deterministic name based on name of the recycled PV, we then get name conflicts when creating the pod.
Two things need to be changed:
- recycler controller and recycler plugins must pass the PV.Name to place, where the pod is created. This is most of the patch and it should be pretty straightforward.
- create recycler pod with deterministic name and check "already exists" error.
When at it, remove useless 'resourceVersion' argument and make log messages starting with lowercase.
There is an unit test to check the behavior + there is an e2e test that checks that regular recycling is not broken (it does not try to run two recycler pods in parallel as the recycler is single-threaded now).
The binder sorts all available volumes first, then it filters out volumes
that cannot be bound by processing each volume in a loop and then finds
the smallest matching volume by binary search.
So, if we process every available volume in a loop, we can also remember the
smallest matching one and save us potentially long sorting (and quick binary
search).
When the controller binds a PV to PVC, it saves both objects to etcd.
However, there is still an old version of these objects in the controller
Informer cache. So, when a new PVC comes, the PV is still seen as available
and may get bound to the new PVC. This will be blocked by etcd, still, it
creates unnecessary traffic that slows everything down.
Also, we save bound PV/PVC as two transactions - we save PV/PVC.Spec first
and then .Status. The controller gets "PV/PVC.Spec updated" event from etcd
and tries to fix the Status, as it seems to the controller it's outdated.
This write again fails - there already is a correct version in etcd.
We can't influence the Informer cache, it is read-only to the controller.
To prevent these useless writes to etcd, this patch introduces second cache
in the controller, which holds latest and greatest version on PVs and PVCs.
It gets updated with events from etcd *and* after etcd confirms successful
save of PV/PVC modified by the controller.
The cache stores only *pointers* to PVs/PVCs, so in ideal case it shares the
actual object data with the informer cache. They will diverge only when
the controller modifies something and the informer cache did not get update
events yet.
Using volume/claim.UID in the operation name is not really useful, as UIDs
are not logged by rest of the controller. On the other hand, volume.Name and
claim.Namespace/Name is logged pretty often and it would help to log these
also in operation name.
This has been already proven to be very useful in controller debugging.
Recycling is a long duration process and when the recycler controller is
restarted in the meantime, it should not start a new recycler pod if there is
one already running.
This means that the recycler pod must have deterministic name based on name
of the recycled PV, we then get name conflicts when creating the pod.
Two things need to be changed:
- recycler controller and recycler plugins must pass the PV.Name to place,
where the pod is created.
- create recycler pod with deterministic name and check "already exists" error.
When at it, remove useless 'resourceVersion' argument and make log messages
starting with lowercase.
- remove persistentvolume_ prefix from all files
- split controller.go into controller.go and controller_base.go (to have them
under 1500 lines for github)
This fixes e2e test for provisioning - it expects that provisioned volumes
are bound quickly.
Majority of this patch is update of test framework needs to initialize the
controller appropriately.
- Add reclaim policy to newVolume() call.
- Implement reactor Volumes().Get().
- Implement mock volume plugin.
- Add recycler tests.
- Add a synchronization condition to controller.scheduleOperation
- we need to pause the controller here, let the test to do some bad things
to the controller and test error cases in recycleVolumeOperation.
Test framework gets more and more complicated... But this is the last piece,
I promise.
We need to keep list of running recyclers, deleters and provisioners in
memory in order not to start a new recycling/deleting/provisioning twice
for the same volume/claim.
This will be eventually replaced by GoRoutineMap from PR #24838.
