Automatic merge from submit-queue
Don't try to attach volumes which are already attached to other nodes
This PR is a replacement for https://github.com/kubernetes/kubernetes/pull/40148. I was not able to push fixes and rebases to the original branch as I don't have access to the Github organization anymore.
CC @saad-ali You probably have to update the PR link in [Q2 2017 (v1.7)](https://docs.google.com/spreadsheets/d/1t4z5DYKjX2ZDlkTpCnp18icRAQqOE85C1T1r2gqJVck/edit#gid=14624465)
I assume the PR will need a new "ok to test"
**ORIGINAL PR DESCRIPTION**
This PR fixes an issue with the attach/detach volume controller. There are cases where the `desiredStateOfWorld` contains the same volume for multiple nodes, resulting in the attach/detach controller attaching this volume to multiple nodes. This of course fails for volumes like AWS EBS, Azure Disks, ...
I observed this situation on Azure when using Azure Disks and replication controllers which start to reschedule PODs. When you delete a POD that belongs to a RC, the RC will immediately schedule a new POD on another node. This results in a short time (max a few seconds) where you have 2 PODs which try to attach/mount the same volume on different nodes. As the old POD is still alive, the attach/detach controller does not try to detach the volume and starts to attach the volume to the new POD immediately.
This behavior was probably not noticed before on other clouds as the bogus attempt to attach probably fails pretty fast and thus is unnoticed. As the situation with the 2 PODs disappears after a few seconds, a detach for the old POD is initiated and thus the new POD can attach successfully.
On Azure however, attaching and detaching takes quite long, resulting in the first bogus attach attempt to already eat up much time.
When attaching fails on Azure and reports that it is already attached somewhere else, the cloud provider immediately does a detach call for the same volume+node it tried to attach to. This is done to make sure the failed attach request is aborted immediately. You can find this here: https://github.com/kubernetes/kubernetes/blob/master/pkg/cloudprovider/providers/azure/azure_storage.go#L74
The complete flow of attach->fail->abort eats up valuable time and the attach/detach controller can not proceed with other work while this is happening. This means, if the old POD disappears in the meantime, the controller can't even start the detach for the volume which delays the whole process of rescheduling and reattaching.
Also, I and other people have observed very strange behavior where disks ended up being "attached" to multiple VMs at the same time as reported by Azure Portal. This results in the controller to fail reattaching forever. It's hard to figure out why and when this happens and there is no reproducer known yet. I can imagine however that the described behavior correlates with what I described above.
I was not sure if there are actually cases where it is perfectly fine to have a volume mounted to multiple PODs/nodes. At least technically, this should be possible with network based volumes, e.g. nfs. Can someone with more knowledge about volumes help me here? I may need to add a check before skipping attaching in `reconcile`.
CC @colemickens @rootfs
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```release-note
Don't try to attach volume to new node if it is already attached to another node and the volume does not support multi-attach.
```
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