From ae2991bcff81f00a56a3afed7a2419592ef187fb Mon Sep 17 00:00:00 2001
From: Brandon Salmon <bsalmon@google.com>
Date: Mon, 6 Oct 2025 19:19:53 +0000
Subject: [PATCH 1/2] First draft of KEP-5620: Node resizing using balloons.

---
 keps/sig-node/5620-resizing-balloon/README.md | 812 ++++++++++++++++++
 keps/sig-node/5620-resizing-balloon/kep.yaml  |  45 +
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 create mode 100644 keps/sig-node/5620-resizing-balloon/README.md
 create mode 100644 keps/sig-node/5620-resizing-balloon/kep.yaml

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+<!--
+**Note:** When your KEP is complete, all of these comment blocks should be removed.
+
+Follow the guidelines of the [documentation style guide].
+In particular, wrap lines to a reasonable length, to make it
+easier for reviewers to cite specific portions, and to minimize diff churn on
+updates.
+
+[documentation style guide]: https://github.com/kubernetes/community/blob/master/contributors/guide/style-guide.md
+
+To get started with this template:
+
+- [ ] **Pick a hosting SIG.**
+  Make sure that the problem space is something the SIG is interested in taking
+  up. KEPs should not be checked in without a sponsoring SIG.
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+  When filing an enhancement tracking issue, please make sure to complete all
+  fields in that template. One of the fields asks for a link to the KEP. You
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+
+Just because a KEP is merged does not mean it is complete or approved. Any KEP
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+
+```
+<<[UNRESOLVED optional short context or usernames ]>>
+Stuff that is being argued.
+<<[/UNRESOLVED]>>
+```
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+When editing KEPS, aim for tightly-scoped, single-topic PRs to keep discussions
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+with suggested changes.
+
+One KEP corresponds to one "feature" or "enhancement" for its whole lifecycle.
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+of this file) is [here](/keps/NNNN-kep-template/README.md).
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+it is marked `implementable`, must be approved by each of the KEP approvers.
+If none of those approvers are still appropriate, then changes to that list
+should be approved by the remaining approvers and/or the owning SIG (or
+SIG Architecture for cross-cutting KEPs).
+-->
+# KEP-5620: Node resizing using balloons
+
+<!--
+This is the title of your KEP. Keep it short, simple, and descriptive. A good
+title can help communicate what the KEP is and should be considered as part of
+any review.
+-->
+
+<!--
+A table of contents is helpful for quickly jumping to sections of a KEP and for
+highlighting any additional information provided beyond the standard KEP
+template.
+
+Ensure the TOC is wrapped with
+  <code>&lt;!-- toc --&rt;&lt;!-- /toc --&rt;</code>
+tags, and then generate with `hack/update-toc.sh`.
+-->
+
+<!-- toc -->
+- [Release Signoff Checklist](#release-signoff-checklist)
+- [Summary](#summary)
+- [Motivation](#motivation)
+  - [Goals](#goals)
+  - [Non-Goals](#non-goals)
+- [Proposal](#proposal)
+  - [User Stories (Optional)](#user-stories-optional)
+    - [Story 1](#story-1)
+    - [Story 2](#story-2)
+  - [Notes/Constraints/Caveats (Optional)](#notesconstraintscaveats-optional)
+  - [Risks and Mitigations](#risks-and-mitigations)
+- [Design Details](#design-details)
+  - [Test Plan](#test-plan)
+      - [Prerequisite testing updates](#prerequisite-testing-updates)
+      - [Unit tests](#unit-tests)
+      - [Integration tests](#integration-tests)
+      - [e2e tests](#e2e-tests)
+  - [Graduation Criteria](#graduation-criteria)
+  - [Upgrade / Downgrade Strategy](#upgrade--downgrade-strategy)
+  - [Version Skew Strategy](#version-skew-strategy)
+- [Production Readiness Review Questionnaire](#production-readiness-review-questionnaire)
+  - [Feature Enablement and Rollback](#feature-enablement-and-rollback)
+  - [Rollout, Upgrade and Rollback Planning](#rollout-upgrade-and-rollback-planning)
+  - [Monitoring Requirements](#monitoring-requirements)
+  - [Dependencies](#dependencies)
+  - [Scalability](#scalability)
+  - [Troubleshooting](#troubleshooting)
+- [Implementation History](#implementation-history)
+- [Drawbacks](#drawbacks)
+- [Alternatives](#alternatives)
+- [Infrastructure Needed (Optional)](#infrastructure-needed-optional)
+<!-- /toc -->
+
+## Release Signoff Checklist
+
+<!--
+**ACTION REQUIRED:** In order to merge code into a release, there must be an
+issue in [kubernetes/enhancements] referencing this KEP and targeting a release
+milestone **before the [Enhancement Freeze](https://git.k8s.io/sig-release/releases)
+of the targeted release**.
+
+For enhancements that make changes to code or processes/procedures in core
+Kubernetes—i.e., [kubernetes/kubernetes], we require the following Release
+Signoff checklist to be completed.
+
+Check these off as they are completed for the Release Team to track. These
+checklist items _must_ be updated for the enhancement to be released.
+-->
+
+Items marked with (R) are required *prior to targeting to a milestone / release*.
+
+- [ ] (R) Enhancement issue in release milestone, which links to KEP dir in [kubernetes/enhancements] (not the initial KEP PR)
+- [ ] (R) KEP approvers have approved the KEP status as `implementable`
+- [ ] (R) Design details are appropriately documented
+- [ ] (R) Test plan is in place, giving consideration to SIG Architecture and SIG Testing input (including test refactors)
+  - [ ] e2e Tests for all Beta API Operations (endpoints)
+  - [ ] (R) Ensure GA e2e tests meet requirements for [Conformance Tests](https://github.com/kubernetes/community/blob/master/contributors/devel/sig-architecture/conformance-tests.md)
+  - [ ] (R) Minimum Two Week Window for GA e2e tests to prove flake free
+- [ ] (R) Graduation criteria is in place
+  - [ ] (R) [all GA Endpoints](https://github.com/kubernetes/community/pull/1806) must be hit by [Conformance Tests](https://github.com/kubernetes/community/blob/master/contributors/devel/sig-architecture/conformance-tests.md) within one minor version of promotion to GA
+- [ ] (R) Production readiness review completed
+- [ ] (R) Production readiness review approved
+- [ ] "Implementation History" section is up-to-date for milestone
+- [ ] User-facing documentation has been created in [kubernetes/website], for publication to [kubernetes.io]
+- [ ] Supporting documentation—e.g., additional design documents, links to mailing list discussions/SIG meetings, relevant PRs/issues, release notes
+
+<!--
+**Note:** This checklist is iterative and should be reviewed and updated every time this enhancement is being considered for a milestone.
+-->
+
+[kubernetes.io]: https://kubernetes.io/
+[kubernetes/enhancements]: https://git.k8s.io/enhancements
+[kubernetes/kubernetes]: https://git.k8s.io/kubernetes
+[kubernetes/website]: https://git.k8s.io/website
+
+## Summary
+
+We provide a resizable node through the use of balloon pods, which acquire, but do not use, resources to ensure that pods on 
+the node cannot consume more than the current size of the node. This allows us to effectively use IPPR to resize
+the node, in addition to using it to resize pods. To decrease the size of a given node, an agent in the system can
+upsize the balloon pod on the given node. To increase the size of a given node, an agent in the sytem can downsize 
+the balloon pod on the given node, allowing other pods to consume more resources on the node itself.
+
+## Motivation
+
+There are several use cases for "resizable nodes". These include dynamic resizing used on top of cloud VMs and testing use cases
+where users would like to easily place multiple kubelets on the same physical host without overloading the host. By using a balloon pod
+we make it easy to quickly increase and decrease the resources allocate to a node in realtime. We also leverage our existing working on 
+pod resource resizing to handle node resizing; pod resizing already needs to handle the various races involved in resizing, we can
+simply leverage that work here rather than needing to re-invent mechanism to handle it.
+
+Note that while this feature is superficially simlar to hotplug, it is orthogonal and complementary to hotplug functionality. Hotplug provides the ability to physically add new hardware to an existing node, which this approach does not provide, but hotplug does not provide an easy way to downsize, since hotunplug of memory in particular, is not easily supportable. Balloons and hotplug can easily coexist; hotplug updates the actual resources available on the underlying machine, and should transparently update the size of a node that is using balloons. Similarly, upsizing and downsizing a node with fixed hardware using a balloon should work transparently in parallel with hotplug operations.
+
+### Goals
+
+ - Provide autoscalers the ability to upsize and downsize Kubernetes nodes in concert with the mechanisms provided by the underlying cloud provider.
+ - Provide an easy way for users to run multiple Kubelets on the same physical host without overloading the underlying host hardware.
+
+### Non-Goals
+
+ - We do not attempt to provide a way to add underlying hardware in this KEP; this can be done either through hotplug or through mechanisms provided by the cloud provider themselves.
+
+## Proposal
+
+We propose that Kubernetes provide an official "balloon pod" concept. Balloon pods are deployed to each node in the sytem using a daemon set controller which can be enabled or disabled by administrators on a given cluster. Balloon pods claim resources using requests, but then do not consume them. This allows the underlying infrastructure to provide only the resources that are unused by the balloons, in whatever way the infrastructure feels appropriate.
+
+To resize a given node, a scaling component can simply invoke in-place-pod-updates on the resources for the balloon pod. To "upsize" the node the component would "downsize" the balloon pod to release more resources to the pods on the node. To "downsize" the node the component would "upsize" the ballon pod to remove resources from the pool available to the pods on the node.
+
+The only distinction between a balloon pod and a standard pod will be annnotations and priority. Balloon pods should get annotations that can be read by system components and used to distinguish between resources "in-use" by normal pods and resources that "don't exist" (used by balloon pods). In addition, balloon pods will have a special priority which makes them as unpreemptable as system-node-critical pods, but unable to preempt other pods when upsized, to ensure that it does not disrupt running customer pods.
+
+### User Stories (Optional)
+
+#### Autoscaling driven VM resizing
+
+A cloud provider would like to provide dynamically resizable Kubernetes nodes. The cloud provider creates a way to manage the resources provided to a particular Kubelet. By enabling the balloon pods and linking the management of the balloon pod sizes with the underlying resources available to the Kubelet host, the cloud provider can upsize and downsize the Kubernetes nodes to the Kubernetes system without having to involve Kubernetes in the specifics of the cloud resizing mechanism.
+
+#### Multiple Kubelets per node for testing
+
+A user who is testing some Kubernetes feature would like to run many Kubelets on the same host to decrease the amount of resources needed to test scenarios with large numbers of Kubelets. By enabling balloons and then resizing the balloons to ensure each Kubelet only consumes one Nth of the host, the customer can place N Kubelets on the same host without overloading the host itself.
+
+### Risks and Mitigations
+
+<!--
+What are the risks of this proposal, and how do we mitigate? Think broadly.
+For example, consider both security and how this will impact the larger
+Kubernetes ecosystem.
+
+How will security be reviewed, and by whom?
+
+How will UX be reviewed, and by whom?
+
+Consider including folks who also work outside the SIG or subproject.
+-->
+
+## Design Details
+
+In general balloon pods will look just like any other pod. They will be scheduled by a daemon set controller and have reservations and limits like any other pod. They will run in the kube-system namespace as system components. The two distinctions are as follows:
+
+ - Balloon pods will be labelled so that monitoring tools can know that the space consumed by the balloon pod "doesn't exist" instead of being "space consumed by a workload". This will be a well known label and potentially require updates to the statistics collection in the Kubernetes master nodes.
+ - Balloon pods will run at a special priority level (system-balloon) which mostly acts like system-node-critical, but instead of preempting other pods on upsize, balloon pods will fail to upsize. This distinction is critical because while the balloon pod should never be preempted (since the underlying capacity "doesn't exist"), we upsize them when we are reclaiming unused space, so if another pod ends up using this space before we reclaim it, we don't want to pre-empt the pod, which would impact a runnin workload, we'd rather fail the reclaim, since we were clearly wrong about it not being needed.
+
+## Metrics details
+
+We will reach out the appropriate sigs for metrics to determine the pod labels should be consumed. We will start with sig-instruments
+
+## Priorities
+
+We will add a new priority (system-node-balloon?) for balloon pods and ensure the priority matches the use cases we care about for balloon pods. In general we would like:
+
+ - For the balloon pods to be considered the same priority as system-node-critical in terms of preemption from other pods.
+ - For the balloon pods to not preempt other pods when we attempt to upsize them.
+
+### Test Plan
+
+<!--
+**Note:** *Not required until targeted at a release.*
+The goal is to ensure that we don't accept enhancements with inadequate testing.
+
+All code is expected to have adequate tests (eventually with coverage
+expectations). Please adhere to the [Kubernetes testing guidelines][testing-guidelines]
+when drafting this test plan.
+
+[testing-guidelines]: https://git.k8s.io/community/contributors/devel/sig-testing/testing.md
+-->
+
+[ ] I/we understand the owners of the involved components may require updates to
+existing tests to make this code solid enough prior to committing the changes necessary
+to implement this enhancement.
+
+##### Prerequisite testing updates
+
+<!--
+Based on reviewers feedback describe what additional tests need to be added prior
+implementing this enhancement to ensure the enhancements have also solid foundations.
+-->
+
+##### Unit tests
+
+<!--
+In principle every added code should have complete unit test coverage, so providing
+the exact set of tests will not bring additional value.
+However, if complete unit test coverage is not possible, explain the reason of it
+together with explanation why this is acceptable.
+-->
+
+<!--
+Additionally, for Alpha try to enumerate the core package you will be touching
+to implement this enhancement and provide the current unit coverage for those
+in the form of:
+- <package>: <date> - <current test coverage>
+The data can be easily read from:
+https://testgrid.k8s.io/sig-testing-canaries#ci-kubernetes-coverage-unit
+
+This can inform certain test coverage improvements that we want to do before
+extending the production code to implement this enhancement.
+-->
+
+- `<package>`: `<date>` - `<test coverage>`
+
+##### Integration tests
+
+<!--
+Integration tests are contained in https://git.k8s.io/kubernetes/test/integration.
+Integration tests allow control of the configuration parameters used to start the binaries under test.
+This is different from e2e tests which do not allow configuration of parameters.
+Doing this allows testing non-default options and multiple different and potentially conflicting command line options.
+For more details, see https://github.com/kubernetes/community/blob/master/contributors/devel/sig-testing/testing-strategy.md
+
+If integration tests are not necessary or useful, explain why.
+-->
+
+<!--
+This question should be filled when targeting a release.
+For Alpha, describe what tests will be added to ensure proper quality of the enhancement.
+
+For Beta and GA, document that tests have been written,
+have been executed regularly, and have been stable.
+This can be done with:
+- permalinks to the GitHub source code
+- links to the periodic job (typically https://testgrid.k8s.io/sig-release-master-blocking#integration-master), filtered by the test name
+- a search in the Kubernetes bug triage tool (https://storage.googleapis.com/k8s-triage/index.html)
+-->
+
+- [test name](https://github.com/kubernetes/kubernetes/blob/2334b8469e1983c525c0c6382125710093a25883/test/integration/...): [integration master](https://testgrid.k8s.io/sig-release-master-blocking#integration-master?include-filter-by-regex=MyCoolFeature), [triage search](https://storage.googleapis.com/k8s-triage/index.html?test=MyCoolFeature)
+
+##### e2e tests
+
+<!--
+This question should be filled when targeting a release.
+For Alpha, describe what tests will be added to ensure proper quality of the enhancement.
+
+For Beta and GA, document that tests have been written,
+have been executed regularly, and have been stable.
+This can be done with:
+- permalinks to the GitHub source code
+- links to the periodic job (typically a job owned by the SIG responsible for the feature), filtered by the test name
+- a search in the Kubernetes bug triage tool (https://storage.googleapis.com/k8s-triage/index.html)
+
+We expect no non-infra related flakes in the last month as a GA graduation criteria.
+If e2e tests are not necessary or useful, explain why.
+-->
+
+- [test name](https://github.com/kubernetes/kubernetes/blob/2334b8469e1983c525c0c6382125710093a25883/test/e2e/...): [SIG ...](https://testgrid.k8s.io/sig-...?include-filter-by-regex=MyCoolFeature), [triage search](https://storage.googleapis.com/k8s-triage/index.html?test=MyCoolFeature)
+
+### Graduation Criteria
+
+<!--
+**Note:** *Not required until targeted at a release.*
+
+Define graduation milestones.
+
+These may be defined in terms of API maturity, [feature gate] graduations, or as
+something else. The KEP should keep this high-level with a focus on what
+signals will be looked at to determine graduation.
+
+Consider the following in developing the graduation criteria for this enhancement:
+- [Maturity levels (`alpha`, `beta`, `stable`)][maturity-levels]
+- [Feature gate][feature gate] lifecycle
+- [Deprecation policy][deprecation-policy]
+
+Clearly define what graduation means by either linking to the [API doc
+definition](https://kubernetes.io/docs/concepts/overview/kubernetes-api/#api-versioning)
+or by redefining what graduation means.
+
+In general we try to use the same stages (alpha, beta, GA), regardless of how the
+functionality is accessed.
+
+[feature gate]: https://git.k8s.io/community/contributors/devel/sig-architecture/feature-gates.md
+[maturity-levels]: https://git.k8s.io/community/contributors/devel/sig-architecture/api_changes.md#alpha-beta-and-stable-versions
+[deprecation-policy]: https://kubernetes.io/docs/reference/using-api/deprecation-policy/
+
+Below are some examples to consider, in addition to the aforementioned [maturity levels][maturity-levels].
+
+#### Alpha
+
+- Feature implemented behind a feature flag
+- Initial e2e tests completed and enabled
+
+#### Beta
+
+- Gather feedback from developers and surveys
+- Complete features A, B, C
+- Additional tests are in Testgrid and linked in KEP
+- More rigorous forms of testing—e.g., downgrade tests and scalability tests
+- All functionality completed
+- All security enforcement completed
+- All monitoring requirements completed
+- All testing requirements completed
+- All known pre-release issues and gaps resolved
+
+**Note:** Beta criteria must include all functional, security, monitoring, and testing requirements along with resolving all issues and gaps identified
+
+#### GA
+
+- N examples of real-world usage
+- N installs
+- Allowing time for feedback
+- All issues and gaps identified as feedback during beta are resolved
+
+**Note:** GA criteria must not include any functional, security, monitoring, or testing requirements.  Those must be beta requirements.
+
+**Note:** Generally we also wait at least two releases between beta and
+GA/stable, because there's no opportunity for user feedback, or even bug reports,
+in back-to-back releases.
+
+**For non-optional features moving to GA, the graduation criteria must include
+[conformance tests].**
+
+[conformance tests]: https://git.k8s.io/community/contributors/devel/sig-architecture/conformance-tests.md
+
+#### Deprecation
+
+<!--
+- Announce deprecation and support policy of the existing flag
+- Two versions passed since introducing the functionality that deprecates the flag (to address version skew)
+- Address feedback on usage/changed behavior, provided on GitHub issues
+- Deprecate the flag
+-->
+
+### Upgrade / Downgrade Strategy
+
+<!--
+If applicable, how will the component be upgraded and downgraded? Make sure
+this is in the test plan.
+
+Consider the following in developing an upgrade/downgrade strategy for this
+enhancement:
+- What changes (in invocations, configurations, API use, etc.) is an existing
+  cluster required to make on upgrade, in order to maintain previous behavior?
+- What changes (in invocations, configurations, API use, etc.) is an existing
+  cluster required to make on upgrade, in order to make use of the enhancement?
+-->
+
+### Version Skew Strategy
+
+<!--
+If applicable, how will the component handle version skew with other
+components? What are the guarantees? Make sure this is in the test plan.
+
+Consider the following in developing a version skew strategy for this
+enhancement:
+- Does this enhancement involve coordinating behavior in the control plane and nodes?
+- How does an n-3 kubelet or kube-proxy without this feature available behave when this feature is used?
+- How does an n-1 kube-controller-manager or kube-scheduler without this feature available behave when this feature is used?
+- Will any other components on the node change? For example, changes to CSI,
+  CRI or CNI may require updating that component before the kubelet.
+-->
+
+## Production Readiness Review Questionnaire
+
+<!--
+
+Production readiness reviews are intended to ensure that features merging into
+Kubernetes are observable, scalable and supportable; can be safely operated in
+production environments, and can be disabled or rolled back in the event they
+cause increased failures in production. See more in the PRR KEP at
+https://git.k8s.io/enhancements/keps/sig-architecture/1194-prod-readiness.
+
+The production readiness review questionnaire must be completed and approved
+for the KEP to move to `implementable` status and be included in the release.
+
+In some cases, the questions below should also have answers in `kep.yaml`. This
+is to enable automation to verify the presence of the review, and to reduce review
+burden and latency.
+
+The KEP must have a approver from the
+[`prod-readiness-approvers`](http://git.k8s.io/enhancements/OWNERS_ALIASES)
+team. Please reach out on the
+[#prod-readiness](https://kubernetes.slack.com/archives/CPNHUMN74) channel if
+you need any help or guidance.
+-->
+
+### Feature Enablement and Rollback
+
+<!--
+This section must be completed when targeting alpha to a release.
+-->
+
+###### How can this feature be enabled / disabled in a live cluster?
+
+<!--
+Pick one of these and delete the rest.
+
+Documentation is available on [feature gate lifecycle] and expectations, as
+well as the [existing list] of feature gates.
+
+[feature gate lifecycle]: https://git.k8s.io/community/contributors/devel/sig-architecture/feature-gates.md
+[existing list]: https://kubernetes.io/docs/reference/command-line-tools-reference/feature-gates/
+-->
+
+- [ ] Feature gate (also fill in values in `kep.yaml`)
+  - Feature gate name:
+  - Components depending on the feature gate:
+- [ ] Other
+  - Describe the mechanism:
+  - Will enabling / disabling the feature require downtime of the control
+    plane?
+  - Will enabling / disabling the feature require downtime or reprovisioning
+    of a node?
+
+###### Does enabling the feature change any default behavior?
+
+<!--
+Any change of default behavior may be surprising to users or break existing
+automations, so be extremely careful here.
+-->
+
+###### Can the feature be disabled once it has been enabled (i.e. can we roll back the enablement)?
+
+<!--
+Describe the consequences on existing workloads (e.g., if this is a runtime
+feature, can it break the existing applications?).
+
+Feature gates are typically disabled by setting the flag to `false` and
+restarting the component. No other changes should be necessary to disable the
+feature.
+
+NOTE: Also set `disable-supported` to `true` or `false` in `kep.yaml`.
+-->
+
+###### What happens if we reenable the feature if it was previously rolled back?
+
+###### Are there any tests for feature enablement/disablement?
+
+<!--
+The e2e framework does not currently support enabling or disabling feature
+gates. However, unit tests in each component dealing with managing data, created
+with and without the feature, are necessary. At the very least, think about
+conversion tests if API types are being modified.
+
+Additionally, for features that are introducing a new API field, unit tests that
+are exercising the `switch` of feature gate itself (what happens if I disable a
+feature gate after having objects written with the new field) are also critical.
+You can take a look at one potential example of such test in:
+https://github.com/kubernetes/kubernetes/pull/97058/files#diff-7826f7adbc1996a05ab52e3f5f02429e94b68ce6bce0dc534d1be636154fded3R246-R282
+-->
+
+### Rollout, Upgrade and Rollback Planning
+
+<!--
+This section must be completed when targeting beta to a release.
+-->
+
+###### How can a rollout or rollback fail? Can it impact already running workloads?
+
+<!--
+Try to be as paranoid as possible - e.g., what if some components will restart
+mid-rollout?
+
+Be sure to consider highly-available clusters, where, for example,
+feature flags will be enabled on some API servers and not others during the
+rollout. Similarly, consider large clusters and how enablement/disablement
+will rollout across nodes.
+-->
+
+###### What specific metrics should inform a rollback?
+
+<!--
+What signals should users be paying attention to when the feature is young
+that might indicate a serious problem?
+-->
+
+###### Were upgrade and rollback tested? Was the upgrade->downgrade->upgrade path tested?
+
+<!--
+Describe manual testing that was done and the outcomes.
+Longer term, we may want to require automated upgrade/rollback tests, but we
+are missing a bunch of machinery and tooling and can't do that now.
+-->
+
+###### Is the rollout accompanied by any deprecations and/or removals of features, APIs, fields of API types, flags, etc.?
+
+<!--
+Even if applying deprecation policies, they may still surprise some users.
+-->
+
+### Monitoring Requirements
+
+<!--
+This section must be completed when targeting beta to a release.
+
+For GA, this section is required: approvers should be able to confirm the
+previous answers based on experience in the field.
+-->
+
+###### How can an operator determine if the feature is in use by workloads?
+
+<!--
+Ideally, this should be a metric. Operations against the Kubernetes API (e.g.,
+checking if there are objects with field X set) may be a last resort. Avoid
+logs or events for this purpose.
+-->
+
+###### How can someone using this feature know that it is working for their instance?
+
+<!--
+For instance, if this is a pod-related feature, it should be possible to determine if the feature is functioning properly
+for each individual pod.
+Pick one more of these and delete the rest.
+Please describe all items visible to end users below with sufficient detail so that they can verify correct enablement
+and operation of this feature.
+Recall that end users cannot usually observe component logs or access metrics.
+-->
+
+- [ ] Events
+  - Event Reason: 
+- [ ] API .status
+  - Condition name: 
+  - Other field: 
+- [ ] Other (treat as last resort)
+  - Details:
+
+###### What are the reasonable SLOs (Service Level Objectives) for the enhancement?
+
+<!--
+This is your opportunity to define what "normal" quality of service looks like
+for a feature.
+
+It's impossible to provide comprehensive guidance, but at the very
+high level (needs more precise definitions) those may be things like:
+  - per-day percentage of API calls finishing with 5XX errors <= 1%
+  - 99% percentile over day of absolute value from (job creation time minus expected
+    job creation time) for cron job <= 10%
+  - 99.9% of /health requests per day finish with 200 code
+
+These goals will help you determine what you need to measure (SLIs) in the next
+question.
+-->
+
+###### What are the SLIs (Service Level Indicators) an operator can use to determine the health of the service?
+
+<!--
+Pick one more of these and delete the rest.
+-->
+
+- [ ] Metrics
+  - Metric name:
+  - [Optional] Aggregation method:
+  - Components exposing the metric:
+- [ ] Other (treat as last resort)
+  - Details:
+
+###### Are there any missing metrics that would be useful to have to improve observability of this feature?
+
+<!--
+Describe the metrics themselves and the reasons why they weren't added (e.g., cost,
+implementation difficulties, etc.).
+-->
+
+### Dependencies
+
+<!--
+This section must be completed when targeting beta to a release.
+-->
+
+###### Does this feature depend on any specific services running in the cluster?
+
+<!--
+Think about both cluster-level services (e.g. metrics-server) as well
+as node-level agents (e.g. specific version of CRI). Focus on external or
+optional services that are needed. For example, if this feature depends on
+a cloud provider API, or upon an external software-defined storage or network
+control plane.
+
+For each of these, fill in the following—thinking about running existing user workloads
+and creating new ones, as well as about cluster-level services (e.g. DNS):
+  - [Dependency name]
+    - Usage description:
+      - Impact of its outage on the feature:
+      - Impact of its degraded performance or high-error rates on the feature:
+-->
+
+### Scalability
+
+<!--
+For alpha, this section is encouraged: reviewers should consider these questions
+and attempt to answer them.
+
+For beta, this section is required: reviewers must answer these questions.
+
+For GA, this section is required: approvers should be able to confirm the
+previous answers based on experience in the field.
+-->
+
+###### Will enabling / using this feature result in any new API calls?
+
+<!--
+Describe them, providing:
+  - API call type (e.g. PATCH pods)
+  - estimated throughput
+  - originating component(s) (e.g. Kubelet, Feature-X-controller)
+Focusing mostly on:
+  - components listing and/or watching resources they didn't before
+  - API calls that may be triggered by changes of some Kubernetes resources
+    (e.g. update of object X triggers new updates of object Y)
+  - periodic API calls to reconcile state (e.g. periodic fetching state,
+    heartbeats, leader election, etc.)
+-->
+
+###### Will enabling / using this feature result in introducing new API types?
+
+<!--
+Describe them, providing:
+  - API type
+  - Supported number of objects per cluster
+  - Supported number of objects per namespace (for namespace-scoped objects)
+-->
+
+###### Will enabling / using this feature result in any new calls to the cloud provider?
+
+<!--
+Describe them, providing:
+  - Which API(s):
+  - Estimated increase:
+-->
+
+###### Will enabling / using this feature result in increasing size or count of the existing API objects?
+
+<!--
+Describe them, providing:
+  - API type(s):
+  - Estimated increase in size: (e.g., new annotation of size 32B)
+  - Estimated amount of new objects: (e.g., new Object X for every existing Pod)
+-->
+
+###### Will enabling / using this feature result in increasing time taken by any operations covered by existing SLIs/SLOs?
+
+<!--
+Look at the [existing SLIs/SLOs].
+
+Think about adding additional work or introducing new steps in between
+(e.g. need to do X to start a container), etc. Please describe the details.
+
+[existing SLIs/SLOs]: https://git.k8s.io/community/sig-scalability/slos/slos.md#kubernetes-slisslos
+-->
+
+###### Will enabling / using this feature result in non-negligible increase of resource usage (CPU, RAM, disk, IO, ...) in any components?
+
+<!--
+Things to keep in mind include: additional in-memory state, additional
+non-trivial computations, excessive access to disks (including increased log
+volume), significant amount of data sent and/or received over network, etc.
+This through this both in small and large cases, again with respect to the
+[supported limits].
+
+[supported limits]: https://git.k8s.io/community//sig-scalability/configs-and-limits/thresholds.md
+-->
+
+###### Can enabling / using this feature result in resource exhaustion of some node resources (PIDs, sockets, inodes, etc.)?
+
+<!--
+Focus not just on happy cases, but primarily on more pathological cases
+(e.g. probes taking a minute instead of milliseconds, failed pods consuming resources, etc.).
+If any of the resources can be exhausted, how this is mitigated with the existing limits
+(e.g. pods per node) or new limits added by this KEP?
+
+Are there any tests that were run/should be run to understand performance characteristics better
+and validate the declared limits?
+-->
+
+### Troubleshooting
+
+<!--
+This section must be completed when targeting beta to a release.
+
+For GA, this section is required: approvers should be able to confirm the
+previous answers based on experience in the field.
+
+The Troubleshooting section currently serves the `Playbook` role. We may consider
+splitting it into a dedicated `Playbook` document (potentially with some monitoring
+details). For now, we leave it here.
+-->
+
+###### How does this feature react if the API server and/or etcd is unavailable?
+
+###### What are other known failure modes?
+
+<!--
+For each of them, fill in the following information by copying the below template:
+  - [Failure mode brief description]
+    - Detection: How can it be detected via metrics? Stated another way:
+      how can an operator troubleshoot without logging into a master or worker node?
+    - Mitigations: What can be done to stop the bleeding, especially for already
+      running user workloads?
+    - Diagnostics: What are the useful log messages and their required logging
+      levels that could help debug the issue?
+      Not required until feature graduated to beta.
+    - Testing: Are there any tests for failure mode? If not, describe why.
+-->
+
+###### What steps should be taken if SLOs are not being met to determine the problem?
+
+## Implementation History
+
+<!--
+Major milestones in the lifecycle of a KEP should be tracked in this section.
+Major milestones might include:
+- the `Summary` and `Motivation` sections being merged, signaling SIG acceptance
+- the `Proposal` section being merged, signaling agreement on a proposed design
+- the date implementation started
+- the first Kubernetes release where an initial version of the KEP was available
+- the version of Kubernetes where the KEP graduated to general availability
+- when the KEP was retired or superseded
+-->
+
+## Drawbacks
+
+<!--
+Why should this KEP _not_ be implemented?
+-->
+
+## Alternatives
+
+<!--
+What other approaches did you consider, and why did you rule them out? These do
+not need to be as detailed as the proposal, but should include enough
+information to express the idea and why it was not acceptable.
+-->
+
+## Infrastructure Needed (Optional)
+
+<!--
+Use this section if you need things from the project/SIG. Examples include a
+new subproject, repos requested, or GitHub details. Listing these here allows a
+SIG to get the process for these resources started right away.
+-->
diff --git a/keps/sig-node/5620-resizing-balloon/kep.yaml b/keps/sig-node/5620-resizing-balloon/kep.yaml
new file mode 100644
index 00000000000..79e42f484ad
--- /dev/null
+++ b/keps/sig-node/5620-resizing-balloon/kep.yaml
@@ -0,0 +1,45 @@
+title: Node resizing via balloons
+kep-number: 5620
+authors:
+  - "@bwsalmon"
+owning-sig: sig-node
+participating-sigs:
+status: provisional
+creation-date: 2025-10-06
+reviewers:
+  - "@liggitt"
+approvers:
+  - "@dawnchen"
+
+see-also:
+  - keps/sig-node/1287-in-place-update-pod-resources
+  - keps/sig-node/3953-node-resource-hot-plug
+
+# The target maturity stage in the current dev cycle for this KEP.
+# If the purpose of this KEP is to deprecate a user-visible feature
+# and a Deprecated feature gates are added, they should be deprecated|disabled|removed.
+stage: alpha
+
+# The most recent milestone for which work toward delivery of this KEP has been
+# done. This can be the current (upcoming) milestone, if it is being actively
+# worked on.
+latest-milestone: "v1.35"
+
+# The milestone at which this feature was, or is targeted to be, at each stage.
+milestone:
+  alpha: "v1.36"
+  beta: "v1.37"
+  stable: "v1.38"
+
+# The following PRR answers are required at alpha release
+# List the feature gate name and the components for which it must be enabled
+feature-gates:
+  - name: MyFeature
+    components:
+      - kube-apiserver
+      - kube-controller-manager
+disable-supported: true
+
+# The following PRR answers are required at beta release
+metrics:
+  - my_feature_metric

From 9f84d09d4fe840abae63aff4dff357a6cbc2dd2e Mon Sep 17 00:00:00 2001
From: Brandon Salmon <bsalmon@google.com>
Date: Mon, 6 Oct 2025 19:30:04 +0000
Subject: [PATCH 2/2] Fix typeo.

---
 keps/sig-node/5620-resizing-balloon/README.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/keps/sig-node/5620-resizing-balloon/README.md b/keps/sig-node/5620-resizing-balloon/README.md
index 70810256ad4..ecd9179a244 100644
--- a/keps/sig-node/5620-resizing-balloon/README.md
+++ b/keps/sig-node/5620-resizing-balloon/README.md
@@ -227,7 +227,7 @@ In general balloon pods will look just like any other pod. They will be schedule
 
 ## Metrics details
 
-We will reach out the appropriate sigs for metrics to determine the pod labels should be consumed. We will start with sig-instruments
+We will reach out the appropriate sigs for metrics to determine the pod labels should be consumed. We will start with sig-instrumentation.
 
 ## Priorities