Craig Condit created YUNIKORN-3058:
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Summary: [UMBRELLA] Support InPlacePodVerticalScaling (phase 3)
Key: YUNIKORN-3058
URL: https://issues.apache.org/jira/browse/YUNIKORN-3058
Project: Apache YuniKorn
Issue Type: Improvement
Components: core - scheduler, shim - kubernetes
Reporter: Craig Condit
Assignee: Craig Condit
Kubernetes 1.27 added a new [InPlacePodVerticalScaling|http://example.com/]
feature. While this is currently still in an alpha state as of 1.32 (and
therefore requires a feature flag to enable), it will be moved to beta in 1.33,
meaning it will be enabled by default, and considered stable in an upcoming
release. The implementation of this feature has implications for YuniKorn, as
with the feature enabled, the requests and limits of a Pod are no longer
immutable.
Fortunately, the updated API objects that enable the feature contain the new
fields so we can add initial support for the feature now. To enable the feature
for testing in a Kind cluster, the kind cluster configuration needs to contain
the following:
{noformat}
kind: Cluster
apiVersion: kind.x-k8s.io/v1alpha4
featureGates:
"InPlacePodVerticalScaling": true{noformat}
During scheduling of new pods, the requested resources are still used as before.
However, once a pod has been started, the actual resource utilization needs to
be tracked via a new {{Pod.Status.ContainerStatuses[].AllocatedResources}}
collection. In addition, if the value of {{Pod.Status.Resize}} is set to
{{{}Proposed{}}}, the usage of each container needs to be computed as the
maximum of its requested and allocated resources. The requested resources field
becomes mutable once this feature is turned on, and it represents the latest
*requested* (not actual) usage of the container.
Supporting this feature is not optional within YuniKorn, as failure to process
the updated resources will mean that we do not account for resource usage
correctly if a pod is updated.
Several steps will need to be taken to support this properly:
* Ensure that GetPodResources() accurately computes the effective usage of the
Pod in all cases. Since the AllocatedResources field will not be populated when
this feature is not active, and is only set once the pod is in a running
statue, this is fairly straightforward and can be implemented even in clusters
which do not have this feature enabled.
* The result of GetPodResources() will need to be cached in the shim so that
we can detect resource changes on Pod updates. Comparing the result of
GetPodResources() on the new Pod vs. the existing version will allow us to
easily detect changes.
* If changes are detected to a running YuniKorn-managed pod, an update message
will need to be sent from the core to change the resources of the allocated
task.
* If changes are detected to a running non-Yunikorn-managed pod, and update of
the node utilized resources will need to be sent from the shim to the core.
* The core *must not* reject these updates, even if they would cause a queue
to go over capacity. Instead, they must be applied to the appropriate ask or
allocation unconditionally.
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