Initial commit to explain the dockershim deprecation (#25359)
* Initial commit to explain the dockershim deprecation Signed-off-by: Jorge O. Castro <jorgec@vmware.com> * Fix overly long links so they render correctly Signed-off-by: Jorge O. Castro <jorgec@vmware.com> * Add author byline Signed-off-by: Jorge O. Castro <jorgec@vmware.com>pull/25355/head
Jorge O. Castro
GitHub
parent
29801cc8e4
commit
9e71e76034
content/en/blog/_posts
|
|
@ -0,0 +1,102 @@
|
|||
---
|
||||
layout: blog
|
||||
title: "Don't Panic: Kubernetes and Docker"
|
||||
date: 2020-12-02
|
||||
slug: dont-panic-kubernetes-and-docker
|
||||
---
|
||||
|
||||
**Authors:** Jorge Castro, Duffie Cooley, Kat Cosgrove, Justin Garrison, Noah Kantrowitz, Bob Killen, Rey Lejano, Dan “POP” Papandrea, Jeffrey Sica, Davanum “Dims” Srinivas
|
||||
|
||||
Kubernetes is [deprecating
|
||||
Docker](https://github.com/kubernetes/kubernetes/blob/master/CHANGELOG/CHANGELOG-1.20.md#deprecation)
|
||||
as a container runtime after v1.20.
|
||||
|
||||
**You do not need to panic. It’s not as dramatic as it sounds.**
|
||||
|
||||
tl;dr Docker as an underlying runtime is being deprecated in favor of runtimes
|
||||
that use the [Container Runtime Interface(CRI)](https://kubernetes.io/blog/2016/12/container-runtime-interface-cri-in-kubernetes/)
|
||||
created for Kubernetes. Docker-produced images will continue to work in your
|
||||
cluster with all runtimes, as they always have.
|
||||
|
||||
If you’re an end-user of Kubernetes, not a whole lot will be changing for you.
|
||||
This doesn’t mean the death of Docker, and it doesn’t mean you can’t, or
|
||||
shouldn’t, use Docker as a development tool anymore. Docker is still a useful
|
||||
tool for building containers, and the images that result from running `docker
|
||||
build` can still run in your Kubernetes cluster.
|
||||
|
||||
If you’re using a managed Kubernetes service like GKE or EKS, you will need to
|
||||
make sure your worker nodes are using a supported container runtime before
|
||||
Docker support is removed in a future version of Kubernetes. If you have node
|
||||
customizations you may need to update them based on your environment and runtime
|
||||
requirements. Please work with your service provider to ensure proper upgrade
|
||||
testing and planning.
|
||||
|
||||
If you’re rolling your own clusters, you will also need to make changes to avoid
|
||||
your clusters breaking. At v1.20, you will get a deprecation warning for Docker.
|
||||
When Docker runtime support is removed in a future release (currently planned
|
||||
for the 1.23 release in late 2021) of Kubernetes it will no longer be supported
|
||||
and you will need to switch to one of the other compliant container runtimes,
|
||||
like containerd or CRI-O. Just make sure that the runtime you choose supports
|
||||
the docker daemon configurations you currently use (e.g. logging).
|
||||
|
||||
## So why the confusion and what is everyone freaking out about?
|
||||
|
||||
We’re talking about two different environments here, and that’s creating
|
||||
confusion. Inside of your Kubernetes cluster, there’s a thing called a container
|
||||
runtime that’s responsible for pulling and running your container images. Docker
|
||||
is a popular choice for that runtime (other common options include containerd
|
||||
and CRI-O), but Docker was not designed to be embedded inside Kubernetes, and
|
||||
that causes a problem.
|
||||
|
||||
You see, the thing we call “Docker” isn’t actually one thing -- it’s an entire
|
||||
tech stack, and one part of it is a thing called “containerd,” which is a
|
||||
high-level container runtime by itself. Docker is cool and useful because it has
|
||||
a lot of UX enhancements that make it really easy for humans to interact with
|
||||
while we’re doing development work, but those UX enhancements aren’t necessary
|
||||
for Kubernetes, because it isn’t a human.
|
||||
|
||||
As a result of this human-friendly abstraction layer, your Kubernetes cluster
|
||||
has to use another tool called Dockershim to get at what it really needs, which
|
||||
is containerd. That’s not great, because it gives us another thing that has to
|
||||
be maintained and can possibly break. What’s actually happening here is that
|
||||
Dockershim is being removed from Kubelet as early as v1.23 release, which
|
||||
removes support for Docker as a container runtime as a result. You might be
|
||||
thinking to yourself, but if containerd is included in the Docker stack, why
|
||||
does Kubernetes need the Dockershim?
|
||||
|
||||
Docker isn’t compliant with CRI, the [Container Runtime Interface](https://kubernetes.io/blog/2016/12/container-runtime-interface-cri-in-kubernetes/).
|
||||
If it were, we wouldn’t need the shim, and this wouldn’t be a thing. But it’s
|
||||
not the end of the world, and you don’t need to panic -- you just need to change
|
||||
your container runtime from Docker to another supported container runtime.
|
||||
|
||||
One thing to note: If you are relying on the underlying docker socket
|
||||
(/var/run/docker.sock) as part of a workflow within your cluster today, moving
|
||||
to a different runtime will break your ability to use it. This pattern is often
|
||||
called Docker in Docker. There are lots of options out there for this specific
|
||||
use case including things like
|
||||
[kaniko](https://github.com/GoogleContainerTools/kaniko),
|
||||
[img](https://github.com/genuinetools/img), and
|
||||
[buildah](https://github.com/containers/buildah).
|
||||
|
||||
## What does this change mean for developers, though? Do we still write Dockerfiles? Do we still build things with Docker?
|
||||
|
||||
This change addresses a different environment than most folks use to interact
|
||||
with Docker. The Docker installation you’re using in development is unrelated to
|
||||
the Docker runtime inside your Kubernetes cluster. It’s confusing, I know. As a
|
||||
developer, Docker is still useful to you in all the ways it was before this
|
||||
change was announced. The image that Docker produces isn’t really a
|
||||
Docker-specific image -- it’s an OCI ([Open Container Initiative](https://opencontainers.org/)) image.
|
||||
Any OCI-compliant image, regardless of the tool you use to build it, will look
|
||||
the same to Kubernetes. Both [containerd](https://containerd.io/) and
|
||||
[CRI-O](https://cri-o.io/) know how to pull those images and run them. This is
|
||||
why we have a standard for what containers should look like.
|
||||
|
||||
So, this change is coming. It’s going to cause issues for some, but it isn’t
|
||||
catastrophic, and generally it’s a good thing. Depending on how you interact
|
||||
with Kubernetes, this could mean nothing to you, or it could mean a bit of work.
|
||||
In the long run, it’s going to make things easier. If this is still confusing
|
||||
for you, that’s okay -- there’s a lot going on here, Kubernetes has a lot of
|
||||
moving parts, and nobody is an expert in 100% of it. We encourage any and all
|
||||
questions regardless of experience level or complexity! Our goal is to make sure
|
||||
everyone is educated as much as possible on the upcoming changes. `<3` We hope
|
||||
this has answered most of your questions and soothed some anxieties!
|
||||
Loading…
Reference in New Issue