Skip to content

Latest commit

 

History

History
304 lines (245 loc) · 13.1 KB

certified-kubernetes-administrator-kubectl.md

File metadata and controls

304 lines (245 loc) · 13.1 KB

Certified Kubernetes Administrator (CKA)

Kubectl Autocomplete

source <(kubectl completion bash) # setup autocomplete in bash, bash-completion package should be installed first.
source <(kubectl completion zsh)  # setup autocomplete in zsh
echo "source <(kubectl completion bash)" >> ~/.bashrc # do the bash autocomplete permanently

Kubectl Context and Configuration

Set which Kubernetes cluster kubectl communicates with and modifies configuration information.

kubectl config view # Show Merged kubeconfig settings (located in ~/.kube/config)

# use multiple kubeconfig files at the same time and view merged config
KUBECONFIG=~/.kube/config:~/.kube/kubconfig2 kubectl config view

# Get the password for the e2e user
kubectl config view -o jsonpath='{.users[?(@.name == "e2e")].user.password}'

kubectl config current-context              # Display the current-context
kubectl config use-context my-cluster-name  # set the default context to my-cluster-name

# add a new cluster to your kubeconf that supports basic auth
kubectl config set-credentials kubeuser/foo.kubernetes.com --username=kubeuser --password=kubepassword

# set a context utilizing a specific username and namespace.
kubectl config set-context gce --user=cluster-admin --namespace=foo \
  && kubectl config use-context gce

Creating Objects

Kubernetes manifests can be defined in json or yaml. The file extension .yaml, .yml, and .json can be used.

kubectl create -f ./my-manifest.yaml           # create resource(s)
kubectl create -f ./my1.yaml -f ./my2.yaml     # create from multiple files
kubectl create -f ./dir                        # create resource(s) in all manifest files in dir
kubectl create -f https://git.io/vPieo         # create resource(s) from url
kubectl run nginx --image=nginx                # start a single instance of nginx
kubectl explain pods,svc                       # get the documentation for pod and svc manifests

# Create multiple YAML objects from stdin
cat <<EOF | kubectl create -f -
apiVersion: v1
kind: Pod
metadata:
  name: busybox-sleep
spec:
  containers:
  - name: busybox
    image: busybox
    args:
    - sleep
    - "1000000"
---
apiVersion: v1
kind: Pod
metadata:
  name: busybox-sleep-less
spec:
  containers:
  - name: busybox
    image: busybox
    args:
    - sleep
    - "1000"
EOF

# Create a secret with several keys
cat <<EOF | kubectl create -f -
apiVersion: v1
kind: Secret
metadata:
  name: mysecret
type: Opaque
data:
  password: $(echo -n "s33msi4" | base64)
  username: $(echo -n "jane" | base64)
EOF

Viewing, Finding Resources

# Get commands with basic output
kubectl get services                          # List all services in the namespace
kubectl get namespaces                        # List all namespaces
kubectl get pods --all-namespaces             # List all pods in all namespaces
kubectl get pods -o wide                      # List all pods in the namespace, with more details
kubectl get deployment my-dep                 # List a particular deployment
kubectl get pods --include-uninitialized      # List all pods in the namespace, including uninitialized ones

# Describe commands with verbose output
kubectl describe nodes my-node
kubectl describe pods my-pod

kubectl get services --sort-by=.metadata.name # List Services Sorted by Name

# List pods Sorted by Restart Count
kubectl get pods --sort-by='.status.containerStatuses[0].restartCount'

# Get the version label of all pods with label app=cassandra
kubectl get pods --selector=app=cassandra rc -o \
  jsonpath='{.items[*].metadata.labels.version}'

# Get all running pods in the namespace
kubectl get pods --field-selector=status.phase=Running

# Get ExternalIPs of all nodes
kubectl get nodes -o jsonpath='{.items[*].status.addresses[?(@.type=="ExternalIP")].address}'

# List Names of Pods that belong to Particular RC
# "jq" command useful for transformations that are too complex for jsonpath, it can be found at https://stedolan.github.io/jq/
sel=${$(kubectl get rc my-rc --output=json | jq -j '.spec.selector | to_entries | .[] | "\(.key)=\(.value),"')%?}
echo $(kubectl get pods --selector=$sel --output=jsonpath={.items..metadata.name})

# Check which nodes are ready
JSONPATH='{range .items[*]}{@.metadata.name}:{range @.status.conditions[*]}{@.type}={@.status};{end}{end}' \
 && kubectl get nodes -o jsonpath="$JSONPATH" | grep "Ready=True"

# List all Secrets currently in use by a pod
kubectl get pods -o json | jq '.items[].spec.containers[].env[]?.valueFrom.secretKeyRef.name' | grep -v null | sort | uniq

# List Events sorted by timestamp
kubectl get events --sort-by=.metadata.creationTimestamp

Updating Resources

kubectl rolling-update frontend-v1 -f frontend-v2.json           # Rolling update pods of frontend-v1
kubectl rolling-update frontend-v1 frontend-v2 --image=image:v2  # Change the name of the resource and update the image
kubectl rolling-update frontend --image=image:v2                 # Update the pods image of frontend
kubectl rolling-update frontend-v1 frontend-v2 --rollback        # Abort existing rollout in progress
cat pod.json | kubectl replace -f -                              # Replace a pod based on the JSON passed into stdin

# Force replace, delete and then re-create the resource. Will cause a service outage.
kubectl replace --force -f ./pod.json

# Create a service for a replicated nginx, which serves on port 80 and connects to the containers on port 8000
kubectl expose rc nginx --port=80 --target-port=8000

# Update a single-container pod's image version (tag) to v4
kubectl get pod mypod -o yaml | sed 's/\(image: myimage\):.*$/\1:v4/' | kubectl replace -f -

kubectl label pods my-pod new-label=awesome                      # Add a Label
kubectl annotate pods my-pod icon-url=http://goo.gl/XXBTWq       # Add an annotation
kubectl autoscale deployment foo --min=2 --max=10                # Auto scale a deployment "foo"

Patching Resources

kubectl patch node k8s-node-1 -p '{"spec":{"unschedulable":true}}' # Partially update a node

# Update a container's image; spec.containers[*].name is required because it's a merge key
kubectl patch pod valid-pod -p '{"spec":{"containers":[{"name":"kubernetes-serve-hostname","image":"new image"}]}}'

# Update a container's image using a json patch with positional arrays
kubectl patch pod valid-pod --type='json' -p='[{"op": "replace", "path": "/spec/containers/0/image", "value":"new image"}]'

# Disable a deployment livenessProbe using a json patch with positional arrays
kubectl patch deployment valid-deployment  --type json   -p='[{"op": "remove", "path": "/spec/template/spec/containers/0/livenessProbe"}]'

# Add a new element to a positional array 
kubectl patch sa default --type='json' -p='[{"op": "add", "path": "/secrets/1", "value": {"name": "whatever" } }]'

Editing Resources

The edit any API resource in an editor.

kubectl edit svc/docker-registry                      # Edit the service named docker-registry
KUBE_EDITOR="nano" kubectl edit svc/docker-registry   # Use an alternative editor

Scaling Resources

kubectl scale --replicas=3 rs/foo                                 # Scale a replicaset named 'foo' to 3
kubectl scale --replicas=3 -f foo.yaml                            # Scale a resource specified in "foo.yaml" to 3
kubectl scale --current-replicas=2 --replicas=3 deployment/mysql  # If the deployment named mysql's current size is 2, scale mysql to 3
kubectl scale --replicas=5 rc/foo rc/bar rc/baz                   # Scale multiple replication controllers

Deleting Resources

kubectl delete -f ./pod.json                                              # Delete a pod using the type and name specified in pod.json
kubectl delete pod,service baz foo                                        # Delete pods and services with same names "baz" and "foo"
kubectl delete pods,services -l name=myLabel                              # Delete pods and services with label name=myLabel
kubectl delete pods,services -l name=myLabel --include-uninitialized      # Delete pods and services, including uninitialized ones, with label name=myLabel
kubectl -n my-ns delete po,svc --all                                      # Delete all pods and services, including uninitialized ones, in namespace my-ns,

Interacting with running Pods

kubectl logs my-pod                                 # dump pod logs (stdout)
kubectl logs my-pod -c my-container                 # dump pod container logs (stdout, multi-container case)
kubectl logs -f my-pod                              # stream pod logs (stdout)
kubectl logs -f my-pod -c my-container              # stream pod container logs (stdout, multi-container case)
kubectl run -i --tty busybox --image=busybox -- sh  # Run pod as interactive shell
kubectl attach my-pod -i                            # Attach to Running Container
kubectl port-forward my-pod 5000:6000               # Listen on port 5000 on the local machine and forward to port 6000 on my-pod
kubectl exec my-pod -- ls /                         # Run command in existing pod (1 container case)
kubectl exec my-pod -c my-container -- ls /         # Run command in existing pod (multi-container case)
kubectl top pod POD_NAME --containers               # Show metrics for a given pod and its containers

Interacting with Nodes and Cluster

kubectl cordon my-node                                                # Mark my-node as unschedulable
kubectl drain my-node                                                 # Drain my-node in preparation for maintenance
kubectl uncordon my-node                                              # Mark my-node as schedulable
kubectl top node my-node                                              # Show metrics for a given node
kubectl cluster-info                                                  # Display addresses of the master and services
kubectl cluster-info dump                                             # Dump current cluster state to stdout
kubectl cluster-info dump --output-directory=/path/to/cluster-state   # Dump current cluster state to /path/to/cluster-state

# If a taint with that key and effect already exists, its value is replaced as specified.
kubectl taint nodes foo dedicated=special-user:NoSchedule

Resource types

The following table includes a list of all the supported resource types and their abbreviated aliases:

Resource type Abbreviated alias
all -
certificatesigningrequests csr
clusterrolebindings -
clusterroles -
componentstatuses cs
configmaps cm
controllerrevisions -
cronjobs -
customresourcedefinition crd, crds
daemonsets ds
deployments deploy
endpoints ep
events ev
horizontalpodautoscalers hpa
ingresses ing
jobs -
limitranges limits
namespaces ns
networkpolicies netpol
nodes no
persistentvolumeclaims pvc
persistentvolumes pv
poddisruptionbudgets pdb
podpreset -
pods po
podsecuritypolicies psp
podtemplates -
replicasets rs
replicationcontrollers rc
resourcequotas quota
rolebindings -
roles -
secrets -
serviceaccount sa
services svc
statefulsets sts
storageclasses sc

Formatting output

To output details to your terminal window in a specific format, you can add either the -o or -output flags to a supported kubectl command.

Output format Description
-o=custom-columns=<spec> Print a table using a comma separated list of custom columns
-o=custom-columns-file=<filename> Print a table using the custom columns template in the <filename> file
-o=json Output a JSON formatted API object
-o=jsonpath=<template> Print the fields defined in a jsonpath expression
-o=jsonpath-file=<filename> Print the fields defined by the jsonpath expression in the <filename> file
-o=name Print only the resource name and nothing else
-o=wide Output in the plain-text format with any additional information, and for pods, the node name is included
-o=yaml Output a YAML formatted API object

Kubectl output verbosity and debugging

Kubectl verbosity is controlled with the -v or --v flags followed by an integer representing the log level. General Kubernetes logging conventions and the associated log levels are described here.

Verbosity Description
--v=0 Generally useful for this to ALWAYS be visible to an operator.
--v=1 A reasonable default log level if you don't want verbosity.
--v=2 Useful steady state information about the service and important log messages that may correlate to significant changes in the system. This is the recommended default log level for most systems.
--v=3 Extended information about changes.
--v=4 Debug level verbosity.
--v=6 Display requested resources.
--v=7 Display HTTP request headers.
--v=8 Display HTTP request contents.
--v=9 Display HTTP request contents without truncation of contents.