Kubernetes cheatsheet - part I

Simple commands examples:

- kubectl version

This will display two different versions: the version of the local kubectl tool, as well as the version of the Kubernetes API server

Example:

[root@node4 ~]# kubectl version
Client Version: version.Info{Major:"1", Minor:"15", GitVersion:"v1.15.0", GitCommit:"e8462b5b5dc2584fdcd18e6bcfe9f1e4d970a529", GitTreeState:"clean", BuildDate:"2019-06-19T16:32:14Z", GoVersion:"go1.12.5", Compiler:"gc", Platform:"linux/amd64"}
Server Version: version.Info{Major:"1", Minor:"15", GitVersion:"v1.15.0", GitCommit:"e8462b5b5dc2584fdcd18e6bcfe9f1e4d970a529", GitTreeState:"clean", BuildDate:"2019-06-19T16:32:14Z", GoVersion:"go1.12.5", Compiler:"gc", Platform:"linux/amd64"}

- kubectl get componentstatuses

A good way to verify that cluster is generally healthy

Example:

[root@node4 ~]# kubectl get componentstatuses
NAME                 STATUS    MESSAGE             ERROR
controller-manager   Healthy   ok
scheduler            Healthy   ok
etcd-2               Healthy   {"health":"true"}
etcd-1               Healthy   {"health":"true"}
etcd-0               Healthy   {"health":"true"}

• The** controller-manager** is responsible for running various controllers that regulate behavior in the cluster: for example, ensuring that all of the replicas of a service are available and healthy.
• The scheduler is responsible for placing different pods onto different nodes in the cluster.
• The etcd server is the storage for the cluster where all of the API objects are stored.

- kubectl get nodes [-o wide]

List out all of the nodes in our cluster

Example:

[root@node4 ~]# kubectl get nodes
NAME    STATUS   ROLES    AGE   VERSION
node1   Ready    <none>   31h   v1.15.0
node2   Ready    <none>   31h   v1.15.0
node3   Ready    <none>   31h   v1.15.0
node4   Ready    master   31h   v1.15.0
node5   Ready    master   32h   v1.15.0

- kubectl describe nodes [node-name]

basic information about the node/nodes with useful details

- kubectl get namespaces

Default kubernetes namespace is kube-system

Example:

[root@node4 ~]# kubectl get namespaces
NAME              STATUS   AGE
default           Active   32h
ingress-nginx     Active   32h
kube-node-lease   Active   32h
kube-public       Active   32h
kube-system       Active   32h

- kubectl get daemonSet --namespace=kube-system kube-proxy

Kubernetes proxy is responsible for routing network traffic to load-balanced services in the Kubernetes cluster

Example:

[root@node4 ~]# kubectl get daemonSets --namespace=kube-system kube-proxy
NAME         DESIRED   CURRENT   READY   UP-TO-DATE   AVAILABLE   NODE SELECTOR                 AGE
kube-proxy   5         5         5       5            5           beta.kubernetes.io/os=linux   32h

- kubectl get deployments --namespace=kube-system coredns

Kubernetes also runs a DNS server, which provides naming and discovery for the services that are defined in the cluster

Example:

[root@node4 ~]# kubectl get deployments --namespace=kube-system coredns
NAME      READY   UP-TO-DATE   AVAILABLE   AGE
coredns   2/2     2            2           32h

- kubectl get services --namespace=kube-system coredns

Kubernetes service that performs load-balancing for the DNS server. This information will be populated in /etc/resolv.conf file in each container

Example:

[root@node4 ~]# kubectl get services --namespace=kube-system coredns
NAME      TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)                  AGE
coredns   ClusterIP   10.233.0.3   <none>        53/UDP,53/TCP,9153/TCP   32h

- kubectl get deployments --namespace=kube-system kubernetes-dashboard

Kubernetes UI service

Example:

[root@node4 ~]# kubectl get deployments --namespace=kube-system kubernetes-dashboard
NAME                   READY   UP-TO-DATE   AVAILABLE   AGE
kubernetes-dashboard   1/1     1            1           32h

- kubectl get services --namespace=kube-system kubernetes-dashboard

Kubernetes UI internal IP address and ports

[root@node4 ~]# kubectl get services --namespace=kube-system kubernetes-dashboard
NAME                   TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)   AGE
kubernetes-dashboard   ClusterIP   10.233.40.188   <none>        443/TCP   32h

- kubectl cluster-info [dump]

Display cluster information Dump - collections of debugs

Example:

[root@node4 ~]# kubectl cluster-info
Kubernetes master is running at https://192.168.166.84:6443
coredns is running at https://192.168.166.84:6443/api/v1/namespaces/kube-system/services/coredns:dns/proxy
kubernetes-dashboard is running at https://192.168.166.84:6443/api/v1/namespaces/kube-system/services/https:kubernetes-dashboard:/proxy

Advanced command example:

- kubectl get <resource name> <object>

By default this command will provide human readable limited output. To get detailed output -o json option can be used For precise output for particular object from json output --template option can be used, which is based on jsonpath query language

Example:

[root@node4 ~]# kubectl get pods --namespace=kube-system kubernetes-dashboard-7c547b4c64-cw2fn -o jsonpath --template={.status.hostIP} | xargs
192.168.166.83

Debugging commands:

- kubectl logs [ -c ] [ -f to stream the logs ]

Output logs from pod or container. Adding --previous flag will capture logs from previous instance of the particular container. This is useful if particular container continuously restarting

Example:

[root@node4 ~]# kubectl logs --namespace=kube-system kubernetes-dashboard-7c547b4c64-cw2fn

- kubectl exec --namespace=<namespace name> -it <pod-name> -- <command to execute in pod or container>

Execute some command in pod or container, or bash to interact with container. In order to exit correctly from container: Ctrl + p -> Ctrl + q

Example:

[root@node4 ~]# kubectl exec --namespace=kube-system  -it nginx-proxy-node1 -- /bin/bash --version | grep bash.*version
GNU bash, version 4.4.12(1)-release (x86_64-pc-linux-gnu)

- kubectl cp <pod-name>:/path/to/remote/file /path/to/local/file

Copy from container to local machine or opposite

- kubectl run testapp --image=gcr.io/kuar-demo/kuard-amd64:1

Will be obsolete later with kubectl create command

Command above will create deployment and will start pod named testapp.

To delete deployment as well as all related pods use:

deployment.extensions "testapp" deleted

=======

Example:

[root@node4 ~]# kubectl delete deployments/testapp
deployment.extensions "testapp" deleted

- kubectl apply -f testapp.yaml

Yaml file example:

apiVersion: v1
kind: Pod
metadata:
        name: testapp
spec:
        containers:
                - image: gcr.io/kuar-demo/kuard-amd64:1
                  name: kuard
                  ports:
                        - containerPort: 8080
                          name: http
                          protocol: TCP

Delete pod by name or using created yaml file:

[root@node4 ~]# kubectl delete pods/testapp
pod "testapp" deleted

More kubectl run examples

Nginx service was choosen as example:

1. Create NGINX pod

kubectl run --generator=run-pod/v1 nginx --image nginx 

2. Generate POD manifest YAML file, without creating

kubectl run --generator=run-pod/v1 nginx --image=nginx --dry-run -o yaml

3. Create a deployment

kubectl run --generator=deployment/v1beta1 nginx --image=nginx

4. Generate deployment YAML file, without creating

kubectl run --generator=deployment/v1beta1 nginx --image=nginx --dry-run -o yaml

5. Generate deployment YAML file, without creating with 4 replicas

kubectl run --generator=deployment/v1beta1 nginx --image=nginx --dry-run --replicas=4 -o yaml > nginx-deployment.yaml

Kubectl services and external access

Nodeport - port accesible on the node for given pod ClusterIP - virtual ip inside a cluster for communication between different services LoadBalancer - distribution load across different web servers

Service definition file example for Nodeport:

apiVersion: v1
kind: Service
metadata:
        name: myapp-service

spec:
        type: NodePort
        ports:
                - targetPort: 80
                  port: 80
                  nodePort: 30008
        selector:
                app: myapp
                type: front-end

Service definition file example for ClusterIP:

apiVersion: v1
kind: Service
metadata:
        name: back-end

spec:
        type: ClusterIP
        ports:
                - targetPort: 80
                  port: 80
        selector:
                app: myapp
                type: back-end

Kubectl service related commands

1. Create a Service named redis-service of ClusterIP to expose pod redis on port 6379

kubectl expose pod redis --port=6379 --name redis-service --dry-run -o yaml

kubectl create service clusterip redis --tcp=6379:6379 --dry-run -o yaml

2. Create a service named nginx or type NodePort to expose pod nginx's port 80 on port 30080

kubectl expose pod nginx --port=80 --name nginx-service --dry-run -o yaml

kubectl create service nodeport nginx --tcp=80:80 --node-port=30080 --dry-run -o yaml

Kubectl check rollouts

Check deployments

$ kubectl get deployment
NAME                READY   UP-TO-DATE   AVAILABLE   AGE
myapp-deployment    3/3     3            3           4d11h
netchecker-server   1/1     1            1           38d

Check status of deployment

$ kubectl rollout status deployments/myapp-deployment
deployment "myapp-deployment" successfully rolled out

Check versions of applications

$ kubectl rollout history deployments/myapp-deployment
deployment.extensions/myapp-deployment
REVISION  CHANGE-CAUSE
1         <none>

Detect privileges

$ sudo kubectl get pods --all-namespaces -o jsonpath='{range .items[*]}{range .spec.initContainers[*]}{.image}{"\t"}{.securityContext}{.end}{"\n"}{end}' | sort | uniq

Detect all images used by pods

$ kubectl get pods -n kube-system -l k8s-app=kube-dns -o jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.spec.containers[*].image}{"\n"}{end}'
coredns-78fcdf6894-fh9vj	k8s.gcr.io/coredns:1.1.3
coredns-76fcdf6894-skdg6	k8s.gcr.io/coredns:1.1.3