Add Forensic Container Checkpointing KEP

Signed-off-by: Adrian Reber <areber@redhat.com>

keps/prod-readiness/sig-node/2008.yaml

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+kep-number: 2008
+alpha:
+  approver: "@ehashman"

keps/sig-node/2008-forensic-container-checkpointing/README.md

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+# KEP-2008: Forensic Container Checkpointing
+
+<!-- toc -->
+- [Release Signoff Checklist](#release-signoff-checklist)
+- [Summary](#summary)
+- [Motivation](#motivation)
+  - [Goals](#goals)
+  - [Non-Goals](#non-goals)
+- [Proposal](#proposal)
+  - [Implementation](#implementation)
+  - [User Stories](#user-stories)
+  - [Risks and Mitigations](#risks-and-mitigations)
+- [Design Details](#design-details)
+  - [Future Enhancements](#future-enhancements)
+  - [Test Plan](#test-plan)
+  - [Graduation Criteria](#graduation-criteria)
+    - [Alpha](#alpha)
+    - [Alpha to Beta Graduation](#alpha-to-beta-graduation)
+    - [Beta to GA Graduation](#beta-to-ga-graduation)
+  - [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)
+- [Implementation History](#implementation-history)
+- [Drawbacks](#drawbacks)
+- [Alternatives](#alternatives)
+<!-- /toc -->
+
+## Release Signoff Checklist
+
+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
+- [ ] (R) Graduation criteria is in place
+- [ ] (R) Production readiness review completed
+- [ ] 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
+
+[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
+
+Provide an interface to trigger a container checkpoint for forensic analysis.
+
+## Motivation
+
+Container checkpointing provides the functionality to take a snapshot of a
+running container. The checkpointed container can be transferred to another
+node and the original container will never know that it was checkpointed.
+
+Restoring the container in a sandboxed environment provides a mean to
+forensically analyse a copy of the container to understand if it might
+have been a possible threat. As the analysis is happening on a copy of
+the original container a possible attacker of the original container
+will not be aware of any sandboxed analysis.
+
+### Goals
+
+The goal of this KEP is to introduce *checkpoint* and *restore* to the CRI API.
+This includes extending the *kubelet* API to support checkpointing single
+containers with the forensic use case in mind.
+
+### Non-Goals
+
+Although *checkpoint* and *restore* can be used to implement container
+migration this KEP is only about enabling the forensic use case. Checkpointing
+a pod is not part of this proposal and left for future enhancements.
+
+## Proposal
+
+### Implementation
+
+For the forensic use case we want to offer the functionality to checkpoint a
+container out of a running Pod without stopping the checkpointed container or
+letting the container know that it was checkpointed.
+
+The corresponding code changes for the forensic use case can be found in the
+following pull request:
+
+* https://github.com/kubernetes/kubernetes/pull/104907
+
+The goal is to introduce *checkpoint* and *restore* in a bottom-up approach.
+In a first step we only want to extend the CRI API to trigger a checkpoint
+by the container engine and to have the low level primitives in the *kubelet*
+to trigger a checkpoint. It is necessary to enable the feature gate
+`ContainerCheckpointRestore` to be able to checkpoint containers.
+
+In the corresponding pull request a checkpoint is triggered using the *kubelet*
+API:
+
+```
+curl -skv -X POST "https://localhost:10250/checkpoint/default/counters/wildfly"
+```
+
+For the first implementation we do not want to support restore in the
+*kubelet*. With the focus on the forensic use case the restore should happen
+outside of Kubernetes. The restore is a container engine only operation
+in this first step.
+
+The forensic use case is targeted to be part of the next (1.24) release.
+
+Although this KEP only adds checkpointing support to the kubelet the CRI API in
+the corresponding code pull request is extended to support *checkpoint* and
+*restore* in the CRI API. The reason to add *restore* to the CRI API without
+implementing it in the kubelet is to make development and especially testing
+easier on the container engine level.
+
+### User Stories
+
+To analyze unusual activities in a container, the container should
+be checkpointed without stopping the container or without the container
+knowing it was checkpointed. Using checkpointing it is possible to take
+a copy of a running container for forensic analysis. The container will
+continue to run without knowing a copy was created. This copy can then
+be restored in another (sandboxed) environment in the context of another
+container engine for detailed analysis of a possible attack.
+
+### Risks and Mitigations
+
+In its first implementation the risks are low as it tries to be a CRI API
+change with minimal changes to the kubelet and it is gated by the feature
+gate `ContainerCheckpointRestore`.
+
+## Design Details
+
+The feature gate `ContainerCheckpointRestore` will ensure that the API
+graduation can be done in the standard Kubernetes way.
+
+A kubelet API to trigger the checkpointing of a container will be
+introduced as described in [Implementation](#implementation).
+
+Also see https://github.com/kubernetes/kubernetes/pull/104907 for details.
+
+### Future Enhancements
+
+The initial implementation is only about checkpointing specific containers
+out of a pod. In future versions we probably want to support checkpointing
+complete pods. To checkpoint a complete pod the expectation on the container
+engine would be to do a pod level cgroup freeze before checkpointing the
+containers in the pod to ensure that all containers are checkpointed at the
+same point in time and that the containers do not keep running while other
+containers in the pod are checkpointed.
+
+One possible result of being able to checkpoint and restore containers and pods
+might be the possibility to migrate containers and pods in the future as
+discussed in [#3949](https://github.com/kubernetes/kubernetes/issues/3949).
+
+### Test Plan
+
+For alpha:
+- Unit tests available
+
+For beta:
+- CRI API changes need to be implemented by at least one
+  container engine
+- Enable e2e testing
+
+### Graduation Criteria
+
+#### Alpha
+
+- [ ] Implement the new feature gate and kubelet implementation
+- [ ] Ensure proper tests are in place
+- [ ] Update documentation to make the feature visible
+
+#### Alpha to Beta Graduation
+
+At least one container engine has to have implemented the
+corresponding CRI APIs to introduce e2e test for checkpointing.
+
+- [ ] Enable the feature per default
+- [ ] No major bugs reported in the previous cycle
+
+#### Beta to GA Graduation
+
+TBD
+
+### Upgrade / Downgrade Strategy
+
+No changes are required on upgrade if the container engine supports
+the corresponding CRI API changes.
+
+CRIU needs to be installed, but on most distributions it is already
+a dependency of runc/crun.
+
+### Version Skew Strategy
+
+There is no explicit version skew strategy required because the feature acts as
+a toggle switch.
+
+## Production Readiness Review Questionnaire
+
+### Feature Enablement and Rollback
+
+###### How can this feature be enabled / disabled in a live cluster?
+
+Using the feature gate `ContainerCheckpointRestore` the feature can be enabled.
+
+###### Does enabling the feature change any default behavior?
+
+No.
+
+###### Can the feature be disabled once it has been enabled (i.e. can we roll back the enablement)?
+
+Yes. By disabling the feature gate `ContainerCheckpointRestore` again.
+
+###### What happens if we reenable the feature if it was previously rolled back?
+
+Checkpointing containers will be possible again.
+
+###### Are there any tests for feature enablement/disablement?
+
+Unit tests will temporarily enable the `ContainerCheckpointRestore` feature gate
+to ensure that the unit tests are always running.
+
+## Implementation History
+
+* 2020-09-16: Initial version of this KEP
+* 2020-12-10: Opened pull request showing an end-to-end implementation of a possible use case
+* 2021-02-12: Changed KEP to mention the *experimental* API as suggested in the SIG Node meeting 2021-02-09
+* 2021-04-08: Added section about Pod Lifecycle, Checkpoint Storage, Alternatives and Hooks
+* 2021-07-08: Reworked structure and added missing details
+* 2021-08-03: Added the forensic user story and highlight the goal to implement it in small steps
+* 2021-08-10: Added future work with information about pod level cgroup freezing
+* 2021-09-15: Removed references to first proof of concept implementation
+* 2021-09-21: Mention feature gate `ContainerCheckpointRestore`
+* 2021-09-22: Removed everything which is not directly related to the forensic use case
+* 2022-01-06: Reworked based on review
+
+## Drawbacks
+
+Not aware of any.
+
+## Alternatives
+
+Another possibility to use checkpoint restore would be, for example, to trigger
+the checkpoint by a privileged sidecar container (`CAP_SYS_ADMIN`) and do the
+restore through an Init container.
+
+The reason to integrate checkpoint restore directly into Kubernetes and not
+with helpers like sidecar and init containers is that checkpointing is already,
+for many years, deeply integrated into multiple container runtimes and engines
+and this integration has been reliable and well tested. Going another way in
+Kubernetes would make the whole process much more complicated and fragile. Not
+using checkpoint and restore in Kubernetes through the existing paths of
+runtimes and engines is not well known and maybe not even possible as
+checkpointing and restoring is tightly integrated as it requires much
+information only available by working closely with runtimes and engines.

keps/sig-node/2008-forensic-container-checkpointing/kep.yaml

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+title: Forensic Container Checkpointing
+kep-number: 2008
+authors:
+  - "@adrianreber"
+owning-sig: sig-node
+participating-sigs:
+  - TBD
+status: implementable
+creation-date: 2020-09-16
+last-updated: 2022-01-17
+reviewers:
+  - "@mrunalp"
+  - "@elfinhe"
+approvers:
+  - "@dchen1107"
+prr-approvers:
+  - "@ehashman"
+
+# The target maturity stage in the current dev cycle for this KEP.
+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: "v1.24"
+
+# The milestone at which this feature was, or is targeted to be, at each stage.
+milestone:
+  alpha: "v1.24"
+  beta: "v1.25"
+  stable: "v1.27"
+
+# 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: ContainerCheckpointRestore
+    components:
+      - kubelet
+disable-supported: true
+
+# The following PRR answers are required at beta release
+metrics:
+  - "N/A"