Merge "Add Kata Containers spec"
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License. http://creativecommons.org/licenses/by/3.0/legalcode
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==========================================
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Reintegrate Kata Containers into StarlingX
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==========================================
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Storyboard: https://storyboard.openstack.org/#!/story/2010765
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https://storyboard.openstack.org/#!/story/2010781
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This spec reintegrates Kata Containers into StarlingX. When the migration
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to Debian was made, the Kata containers support wasn't ported. Then, this spec
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aims to port it.
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Problem description
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===================
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Kata Containers is an open source community working to build a secure
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container runtime with lightweight virtual machines that feel and perform
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like containers, but provide stronger workload isolation using hardware
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virtualization technology as a second layer of defense.[0]
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Since there is a performance gap between Kata Containers and conventional
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containers [1], Kata Containers is not used in default unless explicitly
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requirement is found in the Kubernetes's pod configuration file. Or in other
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words, regardless Kata Containers is enabled or not, containers
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currently we have in StarlingX will not use kata container runtime in default,
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unless extra change is made.
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Use Cases
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---------
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With Kata Containers supported in StarlingX, System developers, testers,
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operators, administrators could choose what container runtime to use when run
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a container image, based on their needs. For example, if there is security
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concern for the pod/container, it could be selected to run with kata container.
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For the default case, runc will be selected as default low-level container
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runtime, which is the default low-level runtime for Kubernetes.
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Proposed changes
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================
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The StarlingX has only one container orchestration tool: the Kubernetes. Which
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is currently already configured to use containerd as container runtime.
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As said in the previous sessions, runc will be maintained as the default
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low-level container runtime. Then, to run a pod with Kata, we need to
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explicitly declare our intention. There are two methods to do so:
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1. Use annotation. Add “io.kubernetes.cri.untrusted-workload” annotation in pod
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file.[2]
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2. Use Runtime Class.[3] 1st method is simpler, but it is deprecated.
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2nd method is recommended. Runtime Class is supported in Kubernetes since
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v1.14, and current Kubernetes version in StarlingX master is v1.26.
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So use Runtime Class to select kata container runtime is recommended.
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The Kata Containers version that will be integrated in StarlingX 9.0 is the
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3.1.3. As were not found precompiled debian packages, then, in build-time,
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it will be packaged using statically-linked prebuilt binaries from
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https://github.com/kata-containers/kata-containers/releases.
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And, for compatibility reasons, it will be necessary upgrade the virtualizer
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QEMU from 5.2 to 7.2 version.
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Data model impact
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-----------------
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None. This spec does not change any existing data models.
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REST API impact
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---------------
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None. This spec does not change any existing REST APIs.
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Security impact
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---------------
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There is no sensitive data touch for this feature, except containerd need
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touch certificate/key for local secure registry "registry.local".
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Kata Containers could help enhance system's security by runs in a dedicated
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kernel, providing isolation of network, I/O and memory and can utilize
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hardware-enforced isolation with virtualization VT extensions." [0]
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Other end user impact
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---------------------
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None. This spec does not impact the end user at all.
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Performance Impact
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------------------
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For containers that doesn't use kata-runtime, the performance should be the
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same as previous.
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For containers that use kata-runtime, some performance drop is expected.
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Per Kata Containers website:"Delivers consistent performance as standard Linux
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containers; increased isolation with the performance tax of standard virtual
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machines."[0]
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Also there are two studies regarding the comparative performance between runc
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and Kata Containers that analyzes and quantifies the aforementioned gap. [1][4]
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Other deployer impact
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---------------------
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None. This spec does not impact deployement at all.
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Developer impact
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----------------
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None. This spec does not impact the development at all.
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Upgrade impact
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--------------
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None. This spec does not impact the upgrade process at all.
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Implementation
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==============
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Assignee(s)
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-----------
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Primary assignee:
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Guilherme Batista Leite
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Other contributors:
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David Liu
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Davi Frossard
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Fabio Studyny Higa
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Marcos Paulo Oliveira Silva
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Elson Claudio de Oliveira
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Repos Impacted
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--------------
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* stx-integ
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* stx-virt
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* stx-root
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* stx-metal
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* stx-tools
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Work Items
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----------
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Add kata container
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* Add kata container support
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Add the support in StarlingX for Kata Containers. The prebuilt runtime
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binaries are downloaded and modified to provide customization support.
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Upgrade QEMU from version 5.2 to version 7.2
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* Upgrade QEMU and port patches
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To avoid any kind of incompatibility with Kata Containers 3.1.x version,
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the QEMU upgrade to version 7.2 is necessary.
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Currently, the QEMU version on the host has WRO-specific patches which
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will need to be ported to the new version.
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Investigation and Documentation of Kata Containers Limitations
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* Actualize the existent documentation
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Currently, there is a document [5] that describes the known limitations when
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using Kata Containers, Although, it is out of date. The new version (3.1.3)
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has already had some of these limitations corrected.
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Besides upper work items, there are other work items maybe need added during
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implementation of this spec. Please check the storyboard link in the beginning of
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this spec to get the full work item list.
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Dependencies
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============
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This specification depends upon the open source upstream:
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https://github.com/kata-containers/kata-containers
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https://github.com/qemu/qemu
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Testing
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=======
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System Configurations
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---------------------
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The system configurations assumed for testing are:
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* AIO-SX
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* Standard
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Preconditions
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-------------
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A Runtimeclass should be created for Kata-containers.
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Test Scenarios
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--------------
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* Basic Test: Kata Container pod checking its kernel version.
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* Kata Container support for static CPU policy.
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* Kata Container support for non-static CPU policy.
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* Kata Container support for SR-IOV.
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* Kata Container support for hugepage.
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* Kata Container support for IPV6.
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Documentation Impact
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====================
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The existent end-user Kata Containers documentation will need to be changed.
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Some outdated info and references will need to be updated.
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References
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==========
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[0]: https://katacontainers.io/
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[1]: https://www.stackhpc.com/kata-io-1.html
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[2]: https://github.com/kata-containers/documentation/blob/master/how-to/how-to-use-k8s-with-cri-containerd-and-kata.md#create-an-untrusted-pod-using-kata-containers
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[3]: https://kubernetes.io/docs/concepts/containers/runtime-class/
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[4]: https://gkoslovski.github.io/files/latincom-2021.pdf
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[5]: https://docs.starlingx.io/usertasks/kubernetes/known-limitations.html
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History
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=======
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.. list-table:: Revisions
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:header-rows: 1
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* - Release Name
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- Description
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* - stx-9.0
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- Introduced
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