1. What Is kubectl
kubectl is the command-line tool for Kubernetes. It interacts with the cluster through the API server.
2. Configuring kubectl
kubectl can be configured through ~/.kube/config to connect to one or more clusters.
For details on how to configure it, see: Configure Access to Multiple Clusters. If you need to configure a remote cluster, see: Building a Remote Kubernetes Development Environment.
View the configured clusters:
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| kubectl config get-contexts
CURRENT NAME CLUSTER AUTHINFO NAMESPACE
* minikube minikube minikube
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Select a cluster:
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| kubectl config set-context minikube
Context "minikube" modified.
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3. kubectl Commands
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| kubectl
kubectl controls the Kubernetes cluster manager.
Find more information at: https://kubernetes.io/docs/reference/kubectl/overview/
Basic Commands (Beginner):
create Create a resource from a file or from stdin.
expose Take a replication controller, service, deployment or pod and expose it as a new Kubernetes Service
run Run a particular image on the cluster
set Set specific features on objects
run-container Run a particular image on the cluster. This command is deprecated, use "run" instead
Basic Commands (Intermediate):
get Display one or many resources
explain Documentation of resources
edit Edit a resource on the server
delete Delete resources by filenames, stdin, resources and names, or by resources and label selector
Deploy Commands:
rollout Manage the rollout of a resource
rolling-update Perform a rolling update of the given ReplicationController
scale Set a new size for a Deployment, ReplicaSet, Replication Controller, or Job
autoscale Auto-scale a Deployment, ReplicaSet, or ReplicationController
Cluster Management Commands:
certificate Modify certificate resources.
cluster-info Display cluster info
top Display Resource (CPU/Memory/Storage) usage.
cordon Mark node as unschedulable
uncordon Mark node as schedulable
drain Drain node in preparation for maintenance
taint Update the taints on one or more nodes
Troubleshooting and Debugging Commands:
describe Show details of a specific resource or group of resources
logs Print the logs for a container in a pod
attach Attach to a running container
exec Execute a command in a container
port-forward Forward one or more local ports to a pod
proxy Run a proxy to the Kubernetes API server
cp Copy files and directories to and from containers.
auth Inspect authorization
Advanced Commands:
apply Apply a configuration to a resource by filename or stdin
patch Update field(s) of a resource using strategic merge patch
replace Replace a resource by filename or stdin
convert Convert config files between different API versions
Settings Commands:
label Update the labels on a resource
annotate Update the annotations on a resource
completion Output shell completion code for the specified shell (bash or zsh)
Other Commands:
api-versions Print the supported API versions on the server, in the form of "group/version"
config Modify kubeconfig files
help Help about any command
plugin Runs a command-line plugin
version Print the client and server version information
Usage:
kubectl [flags] [options]
Use "kubectl <command> --help" for more information about a given command.
Use "kubectl options" for a list of global command-line options (applies to all commands).
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Usage syntax:
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| kubectl [command] [TYPE] [NAME] [flags]
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- command, specifies the operation to perform on one or more resources, such as
create, get, describe, delete. - TYPE, specifies the resource type. Resource types are case-insensitive and can be given in singular, plural, or abbreviated form. For example:
kubectl get pod pod_name. - NAME, specifies the name of the resource. Names are case-sensitive. If the name is omitted, detailed information for all resources is displayed. For example:
kubectl get pods. - flags, specifies optional parameters. For example, you can use the -s or -server parameter to specify the address and port of the Kubernetes API server.
4. Deploying Jenkins with kubectl
- Create a Namespace to isolate the service
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| kubectl create namespace jenkins
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- Deploy Jenkins using a Deployment
Add a jenkins-deployment.yaml file.
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| cat jenkins-deployment.yaml
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: jenkins-deployment
spec:
replicas: 1
selector:
matchLabels:
app: jenkins
template:
metadata:
labels:
app: jenkins
spec:
containers:
- name: jenkins
image: jenkins:2.60.3
ports:
- containerPort: 8080
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Run the command to deploy the Deployment.
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| kubectl create -f jenkins-deployment.yaml --namespace=jenkins
deployment.extensions/jenkins-deployment created
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- View related information
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| kubectl describe deployments --namespace=jenkins
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- Create a service to expose the service
Add a jenkins-service.yaml file.
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| cat jenkins-service.yaml
apiVersion: v1
kind: Service
metadata:
name: jenkins
spec:
type: NodePort
ports:
- port: 8080
targetPort: 8080
nodePort: 30000
selector:
app: jenkins
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Run the command to deploy the service; the nodePort parameter specifies the external service port.
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| kubectl create -f jenkins-service.yaml --namespace=jenkins
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- Access the service
Open the link in a browser: http://your_node_host_ip:30000, and you will find that an initial password is required.
- Get the initial access password from the logs
View the Pod name:
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| kubectl get pods --namespace=jenkins
NAME READY STATUS RESTARTS AGE
jenkins-deployment-868cc579df-42lpn 1/1 Running 0 21m
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Get the password:
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| kubectl log jenkins-deployment-868cc579df-42lpn --namespace=jenkins
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In the logs, you can find the initialization password.
5. Restarting a Job in Kubernetes
Taking CentOS 7 as an example:
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| yum install -y https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm
yum install -y jq
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| kubectl get job
job_name
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| kubectl get job job_name -o json | jq 'del(.spec.selector)' | jq 'del(.spec.template.metadata.labels)' | kubectl replace --force -f -
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6. References
