diff --git a/content/en/blog/_posts/2020-12-02-dockershim-faq.md b/content/en/blog/_posts/2020-12-02-dockershim-faq.md new file mode 100644 index 0000000000..cbdd5cd680 --- /dev/null +++ b/content/en/blog/_posts/2020-12-02-dockershim-faq.md @@ -0,0 +1,180 @@ +--- +layout: blog +title: "Dockershim Deprecation FAQ" +date: 2020-12-02 +slug: dockershim-faq +aliases: [ '/dockershim' ] +--- + +This document goes over some frequently asked questions regarding the Dockershim +depreaction announced as a part of the Kubernetes v1.20 release. For more detail +on the deprecation of Docker as a container runtime for Kubernetes kubelets, and +what that means, check out the blog post +[Don't Panic: Kubernetes and Docker](/blog/2020/12/02/dont-panic-kubernetes-and-docker/). + +### Why is dockershim being deprecated? + +Maintaining dockershim has become a heavy burden on the Kubernetes maintainers. +The CRI standard was created to reduce this burden and allow smooth interoperability +of different container runtimes. Docker itself doesn't currently implement CRI, +thus the problem. + +Dockershim was always intended to be a temporary solution (hence the name: shim). +You can read more about the community discussion and planning in the +[Dockershim Removal Kubernetes Enhancement Proposal][drkep]. + +Additionally, features that were largely incompatible with the dockershim, such +as cgroups v2 and user namespaces are being implemented in these newer CRI +runtimes. Removing support for the dockershim will allow further development in +those areas. + +[drkep]: https://github.com/kubernetes/enhancements/tree/master/keps/sig-node/1985-remove-dockershim + +### Can I still use Docker in Kubernetes 1.20? + +Yes, the only thing changing in 1.20 is a single warning log printed at [kubelet] +startup if using Docker as the runtime. + +[kubelet]: /docs/reference/command-line-tools-reference/kubelet/ + + +### When will dockershim be removed? + +Given the impact of this change, we are using an extended deprecation timeline. +It will not be removed before Kubernetes 1.22, meaning the earliest release without +dockershim would be 1.23 in late 2021. We will be working closely with vendors +and other ecosystem groups to ensure a smooth transition and will evaluate things +as the situation evolves. + + +### Will my existing Docker images still work? + +Yes, the images produced from `docker build` will work with all CRI implementations. +All your existing images will still work exactly the same. + + +### What about private images? + +Also yes. All CRI runtimes support the same pull secrets configuration used in +Kubernetes, either via the PodSpec or ServiceAccount. + + +### Are Docker and containers the same thing? + +Docker popularized the Linux containers pattern and has been instrumental in +developing the underlying technology, however containers in Linux have existed +for a long time. The container ecosystem has grown to be much broader than just +Docker. Standards like OCI and CRI have helped many tools grow and thrive in our +ecosystem, some replacing aspects of Docker while others enhance existing +functionality. + + +### Are there examples of folks using other runtimes in production today? + +All Kubernetes project produced artifacts (Kubernetes binaries) are validated +with each release. + +Additionally, the [kind] project has been using containerd for some time and has +seen an improvement in stability for its use case. Kind and containerd are leveraged +multiple times every day to validate any changes to the Kubernetes codebase. Other +related projects follow a similar pattern as well, demonstrating the stability and +usability of other container runtimes. As an example, OpenShift 4.x has been +using the [CRI-O] runtime in production since June 2019. + +For other examples and references you can look at the adopters of containerd and +cri-o, two container runtimes under the Cloud Native Computing Foundation ([CNCF]). +- [containerd](https://github.com/containerd/containerd/blob/master/ADOPTERS.md) +- [CRI-O](https://github.com/cri-o/cri-o/blob/master/ADOPTERS.md) + +[CRI-O]: https://cri-o.io/ +[kind]: https://kind.sigs.k8s.io/ +[CNCF]: https://cncf.io + + +### People keep referencing OCI, what is that? + +OCI stands for the [Open Container Initiative], which standardized many of the +interfaces between container tools and technologies. They maintain a standard +specification for packaging container images (OCI image-spec) and running containers +(OCI runtime-spec). They also maintain an actual implementation of the runtime-spec +in the form of [runc], which is the underlying default runtime for both +[containerd] and [CRI-O]. The CRI builds on these low-level specifications to +provide an end-to-end standard for managing containers. + +[Open Container Initative]: https://opencontainers.org/about/overview/ +[runc]: https://github.com/opencontainers/runc +[containerd]: https://containerd.io/ + + +### Which CRI implementation should I use? + +That’s a complex question and it depends on a lot of factors. If Docker is +working for you, moving to containerd should be a relatively easy swap and +has have strictly better performance and less overhead. However we encourage you +to explore all the options from the [CNCF landscape] in case another would be an +even better fit for your environment. + +[CNCF landscape]: https://landscape.cncf.io/category=container-runtime&format=card-mode&grouping=category + + +### What should I look out for when changing CRI implementations? + +While the underlying containerization code is the same between Docker and most +CRIs (including containerd), there are a few differences around the edges. Some +common things to consider when migrating are: + +- Logging configuration +- Runtime resource limitations +- Node provisioning scripts that call docker or use docker via it's control socket +- Kubectl plugins that require docker CLI or the control socket +- Kubernetes tools that require direct access to Docker (e.g. kube-imagepuller) +- Configuration of functionality like `registry-mirrors` and insecure registries +- Other support scripts or daemons that expect docker to be available and are run + outside of Kubernetes (e.g. monitoring or security agents) +- GPUs or special hardware and how they integrate with your runtime and Kubernetes + +If you use Kubernetes resource requests/limits or file-based log collection +DaemonSets then they will continue to work the same, but if you’ve customized +your dockerd configuration, you’ll need to adapt that for your new container +runtime where possible. + +Another thing to look out for is anything expecting to run for system maintenance +or nested inside a container when building images will no longer work. For the +former, you can use the [`crictl`][cr] tool as a drop-in replacement and for the +latter you can use newer container build options like [img], [buildah], or +[kaniko] that don’t require Docker. + +[cr]: https://github.com/kubernetes-sigs/cri-tools +[img]: https://github.com/genuinetools/img +[buildah]: https://github.com/containers/buildah +[kaniko]: https://github.com/GoogleContainerTools/kaniko + +For containerd, you can start with their [documentation] to see what configuration +options are available as you migrate things over. + +[documentation]: https://github.com/containerd/cri/blob/master/docs/registry.md + +For instructions on how to use containerd and CRI-O with Kubernetes, see the +Kubernetes documentation on [Container Runtimes] + +[Container Runtimes]: /docs/setup/production-environment/container-runtimes + + +### What if I have more questions? + +If you use a vendor-supported Kubernetes distribution, you can ask them about +upgrade plans for their products. For end-user questions, please post them +to our end user community forum: https://discuss.kubernetes.io/. + +You can also check out the excellent blog post +[Wait, Docker is deprecated in Kubernetes now?][dep] a more in-depth technical +discussion of the changes. + +[dep]: https://dev.to/inductor/wait-docker-is-deprecated-in-kubernetes-now-what-do-i-do-e4m + + +### Can I have a hug? + +Always and whenever you want! 🤗🤗 + +