Configure Docker to Manage Resources in Containerd’s k8s.io Namespace

containerddockerkubernetes

I had a Kubernetes cluster with Docker and recently migrate it to containerd, but I still want to use Docker to manage images and containers for Kubernetes because of some compatibility problems.

When using Docker as a runtime, Docker was able to load images so that Kubernetes can use it, and was able to list containers running as Kubernetes pods with docker ps command.

Even after switching to containerd, I can still run and use Docker with it. However as Docker is isolated from Kubernetes world, it's impossible to manage resources in Kubernetes using docker commands.

It seems that Kubernetes is running with containerd's namespace "k8s.io" so I hope I can configure Docker to manage resources in that namespace, is it possible?

Best Answer

I don't think you'll be able to get the Docker CLI to do that as it's not aware of containerd namespaces.

However there's a tool which provides docker CLI like features for containerd, which is nerdctl, and that could be a good option to explore for this.

Related Solutions

Docker – How to debug a docker container initialization

Docker events command may help and Docker logs command can fetch logs even after the image failed to start.

First start docker events in the background to see whats going on.

docker events&

Then run your failing docker run ... command. Then you should see something like the following on screen:

2015-12-22T15:13:05.503402713+02:00 xxxxxxxacd8ca86df9eac5fd5466884c0b42a06293ccff0b5101b5987f5da07d: (from xxx/xxx:latest) die

Then you can get the startup hex id from previous message or the output of the run command. Then you can use it with the logs command:

docker logs <copy the instance id from docker events messages on screen>

You should now see some output from the failed image startup.

As @alexkb suggested in a comment: docker events& can be troublesome if your container is being constantly restarted from something like AWS ECS service. In this scenario it may be easier to get the container hex id out of the logs in /var/log/ecs/ecs-agent.log.<DATE>. Then use docker logs <hex id>.

Docker – From docker containers to Google Kubernetes

Should the time come that I have 15 containers to manage, instead of 5, is there any merit in using Google Kubernetes?

If you run containers on a single server using the Docker daemon and its Remote API sounds appropriate.

If you need to run containers on more than one server, that's where orchestration solutions like Kubernetes, Docker swarm, Fleet, Mesos, Geard becomes useful.

My primary issue here is that 'dockerfiles' are completely different from pod configs.

Because they have different purposes:

Dockerfile specifies how to build a container image from a tree of sources
pod.yaml defines how to schedule (image, command line, volumes, port) a set of co-located containers (sharing network namespace, and volumes) on one of the node of your cluster.

You can see pods as a way to declarative specify a set of docker run --net=container:... -v ... -p ... commands.

Also, is there an 'official', or at least 'definitive', workflow to migrate from Docker containers to 'pods', the native unit of Kubernetes.

There is a small tool in kubernetes/contrib called podex that allow you to generate a pod manifest from image metadata stored in the public registry.

$ go get github.com/GoogleCloudPlatform/kubernetes/contrib/podex
$ podex google/nodejs-hello
id: nodejs-hello
kind: Pod
apiVersion: v1beta1
desiredState:
  manifest:
    version: v1beta2
    containers:
    - name: nodejs-hello
      image: google/nodejs-hello
      ports:
      - name: nodejs-hello-tcp-8080
        containerPort: 8080

Best Answer

Related Solutions

Docker – How to debug a docker container initialization

Docker – From docker containers to Google Kubernetes

Related Topic