TPU Provisioner: Node pool hash comparison #967
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SidneyShen
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Updated to include an interface for interacting with GKE NodePool API in order to add some tests. |
echiugoog
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@nstogner - Is this PR still a WIP or should the title be updated? |
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Updated title |
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https://github.com/GoogleCloudPlatform/ai-on-gke/pull/967/files#r1973622851 |
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Issue:
Today the provisioner just checks if a node pool with the expected name exists for a given workload. If the workload is quickly recreated with a different node selector it is possible that the provisioner will not delete the old node pool in time and it will not think it needs to create a new one since the old one exists.
Fix:
This PR introduces new logic into the provisioner to check that the existing node pool matches the desired node pool via a hash comparison. Hash is calculated at node pool creation time and stored as a node pool label for later comparison.
Secondary issue & fix:
The reconciler responsible for node pool deletion used to watch for changes to Pods (such as being terminated off of a Node) in addition to changes to Nodes (ex: an update to the Node's status by kubelet) in order to know when to check whether a NodePool was free to delete. A historical PR removed the Pod watch causing a regression. As a result, changes to Node objects are now relied on - this can be slow as Node updates are infrequent (a Pod terminating does not result in an update to the Node object).
This secondary issue was fixed by re-adding the Pod watch into the deletion reconciler.