kubectl cheatsheet (OSX/Mac)

October 28, 2019

                                                                           

These k8s/helm/OSX install notes are reproduced from Rick Hightower profile with permission of Rick Hightower.

Shell completion is a must while you are learning Kubernetes.

kubectl: shell completion

Shell Autocompletion set up guide

In 2019, Apple announced that macOS Catalina would now use Zsh (Z Shell) as the default shell, replacing bash. The zsh extends Bourne shell has improvements with features of Bash, ksh, and tcsh.

Add autoload -Uz compinit; compinit; source <(kubectl completion zsh) to .zshrc if you are using bash still follow the instructions at shell Autocompletion set up guide just use the bash tab on that web page.

Now you should get shell completion for all kubeclt commands (e.g., get pods, get pod, create) and resources hello-fbc47cc98-wlj67.

You might as well do this for minikube too if you are using minikube.

% cat .zshrc      
autoload -Uz compinit
compinit

source <(kubectl completion zsh)
source <(minikube completion zsh)

.zshrc


autoload -Uz compinit
compinit
source <(kubectl completion zsh)

...

kubectl: Check Liveness and show pod events using describe

kubectl describe can describe a node, pod or label. It also shows liveness events from a pod.

kubectl describe pod hello-fbc47cc98-wlj67

kubectl: Get information on k8s object document (API) schema using kubectl explain

kubectl explain describes fields for supported resources. The fields are identified using a JSONPath identifier.

This command describes the fields associated with each supported API resource. Fields are identified using a simple JSONPath identifier:

% kubectl explain deploy.spec.replicas

KIND:     Deployment
VERSION:  extensions/v1beta1

FIELD:    replicas <integer>

DESCRIPTION:
     Number of desired pods. This is a pointer to distinguish between explicit
     zero and not specified. Defaults to 1

kubectl: Watch for changes using kubectl get pods –watch

After getting the pods, watch for changes to pods. This command is useful after you run a large helm install and want to see if the associated pods are ready. Many kubectl have a –watch option to watch for changes.


% kubectl get pods  --watch

NAME                                                         READY   STATUS    RESTARTS   AGE
hello-547ffd886c-khfbp                                       1/1     Running   0          4d15h
lumpy-arachnid-prometheus-alertmanager-79ff6d8bcf-ql27z      2/2     Running   0          4d18h
lumpy-arachnid-prometheus-kube-state-metrics-f46d484-k8mj6   1/1     Running   0          4d18h
lumpy-arachnid-prometheus-node-exporter-sf7vb                1/1     Running   0          4d18h
lumpy-arachnid-prometheus-pushgateway-84b5f94d76-cpkjn       1/1     Running   0          4d18h
lumpy-arachnid-prometheus-server-567f96c6bf-kzn2m            2/2     Running   0          4d18h
solemn-salamander-jenkins-555df964d5-8vfbd                   1/1     Running   0          4d18h

It works with other resources as well, e.g., namespaces kubectl get namespaces --watch.

kubectl: edit k8s objects

The kubectl edit command allows you to directly edit k8s objects and resource. This command is useful for debugging and testing.

% kubectl edit deployments hello
deployment.extensions/hello edited

This goes nicely with the watch command above.

% kubectl get pods  --watch      
NAME                                                         READY   STATUS    RESTARTS   AGE
hello-547ffd886c-8bwrq                                       0/1     Running   0          10s
hello-547ffd886c-khfbp                                       1/1     Running   0          4d15h
lumpy-arachnid-prometheus-alertmanager-79ff6d8bcf-ql27z      2/2     Running   0          4d18h
lumpy-arachnid-prometheus-kube-state-metrics-f46d484-k8mj6   1/1     Running   0          4d18h
lumpy-arachnid-prometheus-node-exporter-sf7vb                1/1     Running   0          4d18h
lumpy-arachnid-prometheus-pushgateway-84b5f94d76-cpkjn       1/1     Running   0          4d18h
lumpy-arachnid-prometheus-server-567f96c6bf-kzn2m            2/2     Running   0          4d18h
solemn-salamander-jenkins-555df964d5-8vfbd                   1/1     Running   0          4d18h
hello-547ffd886c-8bwrq                                       1/1     Running   0          41s

See how hello pod replica (hello-547ffd886c-8bwrq) is added as not ready and then changes to ready. This console output happens because I changed the replica count to 2 in the deployment file.

kubectl: get the YAML of a k8s object use -o yaml

You can use -o yaml to get a starter yaml file to edit. (Take off the state and event data from the yaml file).


% kubectl get deployment hello -o yaml

Full example

% kubectl get deployment hello -o yaml > newDeployment.yaml

Edit file and change replica count back to 1 (vi newDeployment.yaml). Then run a diff before you rerun.

kubectl: diff

kubectl diff  -f newDeployment.yaml

...

 spec:
   progressDeadlineSeconds: 600
-  replicas: 2
+  replicas: 1

...

You should always use diff and see if the changes match your expectations just in case someone manually changed files and did not check those changes into git.

Once satisfied, use apply to apply the changes.

kubectl: apply


% kubectl apply  -f newDeployment.yaml

This applied the changes that we edited and diffed earlier. If you check (kubectl get deployment hello -o yaml), you will see the replica count is back to 1.

kubectl: view logs

 % kubectl logs -n default hello-547ffd886c-khfbp

To follow a pod’s log.

% kubectl logs -n default --follow hello-547ffd886c-khfbp

kubectl: debug deploy issues

Let’s say you have an RBAC permission errors, you may want to view the K8s API server. Let’s show how to do that.

First remember the system namespace.

% kubectl get namespaces
NAME                   STATUS   AGE
default                Active   4d19h
kube-node-lease        Active   4d19h
kube-public            Active   4d19h
kube-system            Active   4d19h
kubernetes-dashboard   Active   4d19h

List the pods in the system namespace.


% kubectl -n kube-system get pods
NAME                                       READY   STATUS    RESTARTS   AGE
coredns-5c98db65d4-8dsh6                   1/1     Running   0          4d19h
coredns-5c98db65d4-lfgb4                   1/1     Running   0          4d19h
elasticsearch-logging-w98q5                1/1     Running   0          4d19h
etcd-minikube                              1/1     Running   0          4d19h
fluentd-es-hfl7s                           1/1     Running   0          4d19h
heapster-9j8bw                             1/1     Running   0          4d19h
influxdb-grafana-9fln9                     2/2     Running   0          4d19h
kibana-logging-fplvw                       1/1     Running   0          4d19h
kube-addon-manager-minikube                1/1     Running   0          4d19h
kube-apiserver-minikube                    1/1     Running   0          4d19h
kube-controller-manager-minikube           1/1     Running   0          4d19h
kube-proxy-f2q87                           1/1     Running   0          4d19h
kube-scheduler-minikube                    1/1     Running   0          4d19h
logviewer-8664c4bdcd-4gfjh                 1/1     Running   0          4d19h
nginx-ingress-controller-778fcbd96-dgcdm   1/1     Running   0          4d19h
storage-provisioner                        1/1     Running   0          4d19h
tiller-deploy-548fd5dc4f-fcvrt             1/1     Running   0          4d19h

kubectl watch the k8s api server log

% kubectl logs -n kube-system -f --tail 10 kube-apiserver-minikube

kubectl watch the etcd server log

% kubectl logs -n kube-system -f --tail 10 etcd-minikube

Make a change like an edit the deployment, as shown earlier. See if you see anything in the logs.

kubectl attach to the container

% kubectl attach hello-547ffd886c-khfbp

If you want to see the output directly without logging, do the following.

kubectl run a shell in a container

% kubectl exec -it hello-547ffd886c-khfbp bin/sh
sh-4.2# ls
app  boot  etc     lib    media  opt   root  sbin  sys  usr
bin  dev   home  lib64    mnt    proc  run   srv     tmp  var

The kubectl exec command just runs a shell inside of an existing pod (first container in the pod if you don’t specify a container.)

The kubectl run creates and runs a particular image. This command includes creating a deployment or job to manage the created container.

kubectl: run a command inside of an image (debugging)

% kubectl run hello6 --generator=run-pod/v1 --image  cloudurable/spring_boot_k8s:0.4.0  \
--attach=true --command --restart=Never -- echo "hi mom"
hi mom

kubectl: delete Clean up our misfires.

% kubectl delete  pod hello
pod "hello" deleted
% kubectl delete  pod hello2
pod "hello2" deleted
% kubectl delete  pod hello3
pod "hello3" deleted
% kubectl delete  pod hello4
pod "hello4" deleted
% kubectl delete  pod hello5
pod "hello5" deleted
% kubectl delete  pod hello6

I added this for comical relief. It took me six tries to get kubectl run to work the way I wanted it to.

kubectl: Cluster info for debugging

% kubectl cluster-info      
Kubernetes master is running at https://192.168.64.4:8443
KubeDNS is running at https://192.168.64.4:8443/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy

To really debug what is going on with a cluster try cluster-info dump.

The kubectl cluster-info dump subcommand dumps all of the cluster info which is useful for debugging and troubleshooting cluster problems. The command dumps everything to stdout or a subdirectory, as shown above. More importantly, it dumps all of the logs for every pod in the cluster per namespace and pods.

% kubectl cluster-info   dump
``

You can also log to a directory.

```sh

(⎈ |k8s-kafka:default)  % mkdir dump
(⎈ |k8s-kafka:default) % kubectl cluster-info   dump  --output-directory ./dump

Cluster info dumped to ./dump

(⎈ |k8s-kafka:default) % cd dump     
(⎈ |k8s-kafka:default) % atom .

kubectl: Context

To solve the problem of accessing several k8s environments from the same laptop, kubectl has the concept of contexts. This way you can manage a local cluster (minikube, Kind, Rancher K3s, Docker Desktop K8s), and your production cluster (Azure AKS, AWS EKS, Google GKE, Rancher, etc.)

% kubectl config get-contexts
CURRENT   NAME       CLUSTER      AUTHINFO   NAMESPACE
*         minikube   minikube     minikube   app01
          gke-p      prod         prod_team  app01
          gke-i      integration  qa_team    app01      
          eks        RandD        dev_team   app01

You can also create a new context to manage a different cluster environment.

kubectl config set-context gke-p2 --cluster=eks --namespace=app01
Context "gke-p2" created.

Working with K8s namespaces and context

Use kube-ps1, kubens and kubectx to manage k8s namespaces and contexts. See install instructions for your OS at kubectx. You will also want to install kube-ps1 to see your current context and namespace.

Install kubectx, kubens, and kube-ps1 on mac / osx

brew update
brew install kubectx
brew install kube-ps1

Add kube-ps1 to your shell

 ~ % cat .zshrc
autoload -Uz compinit
compinit

source <(kubectl completion zsh)
source <(minikube completion zsh)

source "/usr/local/opt/kube-ps1/share/kube-ps1.sh"
PS1='$(kube_ps1)'$PS1
...

Using kubectx and kube-ps1

% kubectl config set-context sys --cluster=minikube --namespace=kube-system
Context "sys" created.
(⎈ |minikube:default)richardhightower@Richards-MacBook-Pro ~ % kubectx sys        
Switched to context "sys".

(⎈ |sys:kube-system) ~ % kubectx -       
Switched to context "minikube".

(⎈ |minikube:default) ~ % kubectl get pods
NAME                                                         READY   STATUS    RESTARTS   AGE
hello-547ffd886c-khfbp                                       1/1     Running   1          5d11h
lumpy-arachnid-prometheus-alertmanager-79ff6d8bcf-ql27z      2/2     Running   2          5d13h
lumpy-arachnid-prometheus-kube-state-metrics-f46d484-k8mj6   1/1     Running   1          5d13h
lumpy-arachnid-prometheus-node-exporter-sf7vb                1/1     Running   1          5d13h
lumpy-arachnid-prometheus-pushgateway-84b5f94d76-cpkjn       1/1     Running   1          5d13h
lumpy-arachnid-prometheus-server-567f96c6bf-kzn2m            2/2     Running   2          5d13h
solemn-salamander-jenkins-555df964d5-8vfbd                   1/1     Running   1          5d13h

(⎈ |minikube:default)~ % kubens
default
kube-node-lease
kube-public
kube-system
kubernetes-dashboard

(⎈ |minikube:default) ~ % kubens default
Context "minikube" modified.
Active namespace is "default".

(⎈ |minikube:default) ~ % kubens kube-system
Context "minikube" modified.
Active namespace is "kube-system".

(⎈ |minikube:kube-system) ~ % kubectl get pods
NAME                                       READY   STATUS    RESTARTS   AGE
coredns-5644d7b6d9-9925c                   1/1     Running   0          10m
coredns-5644d7b6d9-nk7l4                   1/1     Running   0          10m
elasticsearch-logging-w98q5                1/1     Running   1          5d14h
etcd-minikube                              1/1     Running   0          10m
fluentd-es-hfl7s                           1/1     Running   1          5d14h
heapster-9j8bw                             1/1     Running   1          5d14h
influxdb-grafana-9fln9                     2/2     Running   2          5d14h
kibana-logging-fplvw                       1/1     Running   1          5d14h
kube-addon-manager-minikube                1/1     Running   0          10m
kube-apiserver-minikube                    1/1     Running   0          10m
kube-controller-manager-minikube           1/1     Running   0          10m
kube-proxy-dpp4d                           1/1     Running   0          10m
kube-scheduler-minikube                    1/1     Running   0          10m
logviewer-8664c4bdcd-4gfjh                 1/1     Running   1          5d14h
nginx-ingress-controller-778fcbd96-dgcdm   1/1     Running   1          5d14h
storage-provisioner                        1/1     Running   1          5d14h
tiller-deploy-548fd5dc4f-fcvrt             1/1     Running   1          5d14h

(⎈ |minikube:kube-system) ~ % kubens default    
Context "minikube" modified.
Active namespace is "default".

(⎈ |minikube:default) ~ % kubectl get pods
NAME                                                         READY   STATUS    RESTARTS   AGE
hello-547ffd886c-khfbp                                       1/1     Running   1          5d11h
lumpy-arachnid-prometheus-alertmanager-79ff6d8bcf-ql27z      2/2     Running   2          5d13h
lumpy-arachnid-prometheus-kube-state-metrics-f46d484-k8mj6   1/1     Running   1          5d13h
lumpy-arachnid-prometheus-node-exporter-sf7vb                1/1     Running   1          5d13h
lumpy-arachnid-prometheus-pushgateway-84b5f94d76-cpkjn       1/1     Running   1          5d13h
lumpy-arachnid-prometheus-server-567f96c6bf-kzn2m            2/2     Running   2          5d13h
solemn-salamander-jenkins-555df964d5-8vfbd                   1/1     Running   1          5d13h

You may also consider kube-sh. The kubed-sh is “the Kubernetes distributed shell for the casual cluster user.” and “lets you execute a program in a Kubernetes cluster without having to create a container image or learn new concepts.”

More to come.

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