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kubectl for Docker Users

In this doc, we introduce the Kubernetes command line for interacting with the api to docker-cli users. The tool, kubectl, is designed to be familiar to docker-cli users but there are a few necessary differences. Each section of this doc highlights a docker subcommand explains the kubectl equivalent.

docker run

How do I run an nginx Deployment and expose it to the world? Checkout kubectl run.

With docker:

$ docker run -d --restart=always -e DOMAIN=cluster --name nginx-app -p 80:80 nginx
a9ec34d9878748d2f33dc20cb25c714ff21da8d40558b45bfaec9955859075d0
$ docker ps
CONTAINER ID        IMAGE               COMMAND                CREATED             STATUS              PORTS                         NAMES
a9ec34d98787        nginx               "nginx -g 'daemon of   2 seconds ago       Up 2 seconds        0.0.0.0:80->80/tcp, 443/tcp   nginx-app

With kubectl:

# start the pod running nginx
$ kubectl run --image=nginx nginx-app --port=80 --env="DOMAIN=cluster"
deployment "nginx-app" created

kubectl run creates a Deployment named “nginx” on Kubernetes cluster >= v1.2. If you are running older versions, it creates replication controllers instead. If you want to obtain the old behavior, use --generator=run/v1 to create replication controllers. See kubectl run for more details. Note that kubectl commands will print the type and name of the resource created or mutated, which can then be used in subsequent commands. Now, we can expose a new Service with the deployment created above:

# expose a port through with a service
$ kubectl expose deployment nginx-app --port=80 --name=nginx-http
service "nginx-http" exposed

With kubectl, we create a Deployment which will make sure that N pods are running nginx (where N is the number of replicas stated in the spec, which defaults to 1). We also create a service with a selector that matches the Deployment’s selector. See the Quick start for more information.

By default images are run in the background, similar to docker run -d ..., if you want to run things in the foreground, use:

kubectl run [-i] [--tty] --attach <name> --image=<image>

Unlike docker run ..., if --attach is specified, we attach to stdin, stdout and stderr, there is no ability to control which streams are attached (docker -a ...).

Because we start a Deployment for your container, it will be restarted if you terminate the attached process (e.g. ctrl-c), this is different than docker run -it. To destroy the Deployment (and its pods) you need to run kubectl delete deployment <name>

docker ps

How do I list what is currently running? Checkout kubectl get.

With docker:

$ docker ps
CONTAINER ID        IMAGE               COMMAND                CREATED             STATUS              PORTS                         NAMES
a9ec34d98787        nginx               "nginx -g 'daemon of   About an hour ago   Up About an hour    0.0.0.0:80->80/tcp, 443/tcp   nginx-app

With kubectl:

$ kubectl get po
NAME              READY     STATUS    RESTARTS   AGE
nginx-app-5jyvm   1/1       Running   0          1h

docker attach

How do I attach to a process that is already running in a container? Checkout kubectl attach

With docker:

$ docker ps
CONTAINER ID        IMAGE               COMMAND                CREATED             STATUS              PORTS                         NAMES
a9ec34d98787        nginx               "nginx -g 'daemon of   8 minutes ago       Up 8 minutes        0.0.0.0:80->80/tcp, 443/tcp   nginx-app
$ docker attach -it a9ec34d98787
...

With kubectl:

$ kubectl get pods
NAME              READY     STATUS    RESTARTS   AGE
nginx-app-5jyvm   1/1       Running   0          10m
$ kubectl attach -it nginx-app-5jyvm
...

docker exec

How do I execute a command in a container? Checkout kubectl exec.

With docker:

$ docker ps
CONTAINER ID        IMAGE               COMMAND                CREATED             STATUS              PORTS                         NAMES
a9ec34d98787        nginx               "nginx -g 'daemon of   8 minutes ago       Up 8 minutes        0.0.0.0:80->80/tcp, 443/tcp   nginx-app
$ docker exec a9ec34d98787 cat /etc/hostname
a9ec34d98787

With kubectl:

$ kubectl get po
NAME              READY     STATUS    RESTARTS   AGE
nginx-app-5jyvm   1/1       Running   0          10m
$ kubectl exec nginx-app-5jyvm -- cat /etc/hostname
nginx-app-5jyvm

What about interactive commands?

With docker:

$ docker exec -ti a9ec34d98787 /bin/sh
# exit

With kubectl:

$ kubectl exec -ti nginx-app-5jyvm -- /bin/sh      
# exit

For more information see Getting into containers.

docker logs

How do I follow stdout/stderr of a running process? Checkout kubectl logs.

With docker:

$ docker logs -f a9e
192.168.9.1 - - [14/Jul/2015:01:04:02 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.35.0" "-"
192.168.9.1 - - [14/Jul/2015:01:04:03 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.35.0" "-"

With kubectl:

$ kubectl logs -f nginx-app-zibvs
10.240.63.110 - - [14/Jul/2015:01:09:01 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.26.0" "-"
10.240.63.110 - - [14/Jul/2015:01:09:02 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.26.0" "-"

Now’s a good time to mention slight difference between pods and containers; by default pods will not terminate if their processes exit. Instead it will restart the process. This is similar to the docker run option --restart=always with one major difference. In docker, the output for each invocation of the process is concatenated but for Kubernetes, each invocation is separate. To see the output from a previous run in Kubernetes, do this:

$ kubectl logs --previous nginx-app-zibvs
10.240.63.110 - - [14/Jul/2015:01:09:01 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.26.0" "-"
10.240.63.110 - - [14/Jul/2015:01:09:02 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.26.0" "-"

See Logging for more information.

docker stop and docker rm

How do I stop and delete a running process? Checkout kubectl delete.

With docker

$ docker ps
CONTAINER ID        IMAGE               COMMAND                CREATED             STATUS              PORTS                         NAMES
a9ec34d98787        nginx               "nginx -g 'daemon of   22 hours ago        Up 22 hours         0.0.0.0:80->80/tcp, 443/tcp   nginx-app
$ docker stop a9ec34d98787
a9ec34d98787
$ docker rm a9ec34d98787
a9ec34d98787

With kubectl:

$ kubectl get deployment nginx-app
NAME        DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
nginx-app   1         1         1            1           2m
$ kubectl get po -l run=nginx-app
NAME                         READY     STATUS    RESTARTS   AGE
nginx-app-2883164633-aklf7   1/1       Running   0          2m
$ kubectl delete deployment nginx-app
deployment "nginx-app" deleted
$ kubectl get po -l run=nginx-app
# Return nothing

Notice that we don’t delete the pod directly. With kubectl we want to delete the Deployment that owns the pod. If we delete the pod directly, the Deployment will recreate the pod.

docker login

There is no direct analog of docker login in kubectl. If you are interested in using Kubernetes with a private registry, see Using a Private Registry.

docker version

How do I get the version of my client and server? Checkout kubectl version.

With docker:

$ docker version
Client version: 1.7.0
Client API version: 1.19
Go version (client): go1.4.2
Git commit (client): 0baf609
OS/Arch (client): linux/amd64
Server version: 1.7.0
Server API version: 1.19
Go version (server): go1.4.2
Git commit (server): 0baf609
OS/Arch (server): linux/amd64

With kubectl:

$ kubectl version
Client Version: version.Info{Major:"0", Minor:"20.1", GitVersion:"v0.20.1", GitCommit:"", GitTreeState:"not a git tree"}
Server Version: version.Info{Major:"0", Minor:"21+", GitVersion:"v0.21.1-411-g32699e873ae1ca-dirty", GitCommit:"32699e873ae1caa01812e41de7eab28df4358ee4", GitTreeState:"dirty"}

docker info

How do I get miscellaneous info about my environment and configuration? Checkout kubectl cluster-info.

With docker:

$ docker info
Containers: 40
Images: 168
Storage Driver: aufs
 Root Dir: /usr/local/google/docker/aufs
 Backing Filesystem: extfs
 Dirs: 248
 Dirperm1 Supported: false
Execution Driver: native-0.2
Logging Driver: json-file
Kernel Version: 3.13.0-53-generic
Operating System: Ubuntu 14.04.2 LTS
CPUs: 12
Total Memory: 31.32 GiB
Name: k8s-is-fun.mtv.corp.google.com
ID: ADUV:GCYR:B3VJ:HMPO:LNPQ:KD5S:YKFQ:76VN:IANZ:7TFV:ZBF4:BYJO
WARNING: No swap limit support

With kubectl:

$ kubectl cluster-info
Kubernetes master is running at https://108.59.85.141
KubeDNS is running at https://108.59.85.141/api/v1/proxy/namespaces/kube-system/services/kube-dns
KubeUI is running at https://108.59.85.141/api/v1/proxy/namespaces/kube-system/services/kube-ui
Grafana is running at https://108.59.85.141/api/v1/proxy/namespaces/kube-system/services/monitoring-grafana
Heapster is running at https://108.59.85.141/api/v1/proxy/namespaces/kube-system/services/monitoring-heapster
InfluxDB is running at https://108.59.85.141/api/v1/proxy/namespaces/kube-system/services/monitoring-influxdb

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