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My CKAD Prep – DEV Community



Desk of Contents



Notes

Earlier than we dive into the templates and instructions, listed here are some notes about Kubernetes that it is best to remember:

Cluster is a set of nodes

Grasp node has:

  • api sever (frontend for kube)
  • etcd (key retailer for knowledge used to handle cluster)
  • scheduler (assigns containers to nodes)
  • controller (carry up containers after they go down)

Labored node has:

  • kubelet (agent in every node in cluster that ensures containers working on nodes as anticipated)
  • runtime (software program to run containers within the background i.e docker)

Multi container pods can talk to one another by way of localhost

Assets in a namespace can refer to one another by their names

pods have a 1 to 1 relationship with containers
entrypoint in docker -> command in kubernetes
cmd in docker -> args in kubernetes
kube system - sources for inside functions for kubernetes
kube public - sources to be made obtainable to all customers
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kubeapiserver path is /and many others/kubernetes/manifests/kube-apiserver.yaml
To verify settings handed to kubeapi server: ps -aux | grep authorization

To view api sources and their shortnames:

kubectl api-resources
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To allow alpha variations: --runtime-config=api/model

Run watch crictl ps to attend for kube api server to come back again on-line

To deal with api deprecations:

kubectl convert -f <old-file> --output-version <new-api-version> > <new-file>
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Now, let’s dive into the templates and instructions you should use for sources.



Pod

Single occasion of an software (smallest object we will create in k8)

We scale pods up or down

kubectl get pods -o large
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kubectl get pods -A
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kubectl label pod/<pod-name> <label>=<worth>
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kubectl get pods,svc
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kubectl get pods --no-headers | wc -l
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kubectl run <pod-name> --image=<image-name>  -n <namespace> --dry-run=shopper -o yaml > take a look at.yaml
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kubectl set picture pod <pod-name> <container-name>=<picture>
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kubectl get pod <pod-name> -o yaml > pod-definition.yaml
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kubectl exec -it podname -- commandtorun
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kubectl exchange --force -f app.yaml
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kubectl apply -f take a look at.yaml
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kubeclt edit pod <pod-name>
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kubectl clarify pods --recursive | much less
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kubectl clarify pods --recursive | grep envFrom -A<number-of-lines>
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kubectl get pods --selector label=worth
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kubectl get pods --selector label=worth,label2=value2
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  • Selectors match labels described i.e match labels on the pod or service to match labels of a pod

  • Annotation information particulars for informatory functions e.g construct info, instrument used.



Replication Controller and Replicaset

Replication controller is in v1 whereas replicaset in apps/v1

Duplicate set makes use of selector to find out pods to observe and handle even current pods
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kubectl create -f definition.yaml
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kubectl get replicationcontroller
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kubectl get rs
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kubectl delete replicaset <replicaset-name>
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kubectl edit replicaset <replicaset-name>
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kubectl set picture rs <replica-set> <container-name>=<picture>
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kubectl describe replicaset <replicaset-name>
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kubectl apply -f definition.yaml
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kubectl exchange -f definition.yaml
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kubectl scale -replicas=10 -f definition.yaml
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kubectl scale --replicas=0 replicaset/<replicaset-name>
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Deployments

kubectl create deployment nginx --image=nginx
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kubectl scale deploy/webapp --replicas=3
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kubectl get deploy
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kubectl get deploy -o large
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kubectl delete deployment <deployment -name>
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kubectl create deploy redis-deploy --image=redis --replicas=2 -n dev-ns
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  • Deployment methods:
    • Recreate – Take away all purposes working on older verision and convey up purposes working on newer verision
    • Rolling replace (default technique) – Take away a single software and convey up a brand new one one after the other till the newer model is working on all purposes
    • A brand new reproduction set is created underneath the hood after we do deployment upgrades
    • We use file flag to avoid wasting instructions used to create/replace deployments
    • We use the to revision flag to rollback to a particular revision 
kubectl set picture deploy/deploymentname <container-name>=<picture>
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kubectl set picture deploy/deploymentname <container-name>=<picture> --record
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kubectl rollout restart deploy/deploymentname
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kubectl rollout standing deploy/deploymentname
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kubectl rollout historical past deploy/deploymentname
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kubectl rollout undo deploy/deploymentname
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kubectl rollout undo deploy/deploymentname --to-revision=1
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Namespaces

kubectl create ns <namespace-name>
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kubectl config set-context $(kubectl config current-context) -n <namespace-name>
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Providers

Allow communication between elements throughout the software

Sorts:

  • Node Port
    • Node Port Definition file
    • Map a port on node to a port on the pod
    • The node’s port Can solely be within the vary 30000 to 32767
    • Node port -> Service -> Goal port (Pod’s port)
    • Node port and repair port usually are not necessary, if not offered, node port is allotted an obtainable ip within the vary 30000 to 32767 whereas service port is assumed to be similar as port
    • Acts as loadbalancer if we’ve a number of pods with the identical label, it makes use of a random algorithm to pick which pod to ship requests to.

  • Cluster Ip

    • Cluster Ip Definition file
    • Service assigned an ip within the cluster and it is used to entry the service by different pods within the service.

  • Load Balancer

    • Builds on prime of node port and permits balancing of requests to the service to it is goal purposes

To connect with one other service in a distinct namespace: we use the next syntax:

<service-name>.<namespace>.<svc>.<area>
test-service.test-ns.svc.cluster.native
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kubectl expose useful resource <resource-name> --type=<kind> --port=<port> --target-port=<target-port> --name=<service-name>
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kubectl create service <kind> <service-name> --tcp=<port>:<port>
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Config Map


  kubectl create configmap 
      app-config --from-literal=APP_COLOR=RED 
                 --from-literal=APP_TYPE=AAB 
                 --from-literal=APP_ENV=PROD
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  kubectl create configmap 
      app-config --from-file=app_config.properties
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  kubectl create -f test-config-map.yaml
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  kubectl get configmaps
  kubectl get cm
  kubectl describe configmap
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Secrets and techniques

  kubectl create secret generic 
      app-secret --from-literal=DB_HOST=mysql 
                 --from-literal=DB_PORT=1000
                 --from-literal=DB_NAME=take a look at
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  kubectl create secret generic 
      app-secret --from-file=take a look at.env
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  kubectl create -f test-secret.yaml
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  kubectl get secrets and techniques
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  kubectl get secret <secret-name> -o yaml
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  kubectl describe secrets and techniques
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Safety Context

We are able to add safety context on the pod degree or the container degree. If each are specified, the container degree takes priority.

Cabapilites are supported solely on the container degree



Service Account

kubectl create serviceaccount test-sa
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kubectl get serviceaccount
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kubectl describe serviceaccount test-sa
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kubectl create token SERVICEACCOUNTNAME
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Taints and Tolerations

kubectl taint nodes NODENAME app=pink:taint-effect
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kubectl taint nodes NODENAME app=pink:taint-effect-
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taint-effects embody: NoSchedule|NoExecute|PreferNoSchedule



Node Selectors

kubectl label nodes NODENAME kind=take a look at
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We can not apply superior filters e.g not , or



Node Affinity

Node affinity sorts:

  • requiredDuringSchedulingIgnoredDuringExecution
  • PreferredDuringSchedulingIgnoredDuringExecution
  • requiredDuringSchedulingrequiredDuringExecution
Throughout Scheduling Throughout Execution
1 Required Ignored
2 Most well-liked Ignored
3 Required Required



Multicontainer Pods

  • Multicontainer Pods Definition file

  • Sidecar containers -> assist the primary container e.g to logging agent to ship logs to log server

  • Adapter containers -> course of knowledge for the primary container e.g converts logs to readable format earlier than sending to logging server

  • Ambassador containers -> proxy requests from the primary container e.g ship requests to db on predominant container’s behalf

  • Init Containers Definition file

  • Init containers -> Course of inside init container should end earlier than different containers begin.

  • If the init container fails, the pod is restarted till the init container succeeds



Observability

Readiness Probe:

  • Carry out take a look at to verify if the container is up earlier than marking the container as prepared.
  • For readiness, we will do http calls, tcp calls or run a command that when succesfull, we mark the container as prepared

Liveness Probe:

  • Periodically take a look at if software inside container is wholesome.

  • For liveness, we will do http calls, tcp calls or run a command that after they fail, we mark the container as unhealthy and it is restarted

  • Readiness & Liveness Probe Definition file

Logging:

Present logs

kubectl logs podname
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Present reside logs

kubectl logs -f podname
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For multi container we specify container title

kubectl logs -f podname container-name
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Metric Server:

  • We are able to have 1 metric server per cluster
  • Receives metrics from nodes and pods and shops them in reminiscence ( we will not see historic knowledge with metric server)
  • To put in on cluster,we clone the metric server repo and run kubectl create -f repourl 
kubectl prime node
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kubectl prime pod
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Jobs and Cronjobs

Job – Duties that may be run and exit after they’ve finalized

kubectl get jobs
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Cronjob – To run jobs periodically

kubectl get cronjob
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Ingress

  • Ingress Definition file

  • Allows customers entry software by way of an externally accessible url that we will configure to path to totally different providers within the cluster primarily based on url path whereas implementing ssl as effectively

  • We have to expose it so it may be accessible exterior the cluster

  • Ingress controller:

    • Doesn’t include kubernetes as default. We have to deploy if first.
    • Examples are istio, nginx, haproxy

  • Ingress sources:

    • Guidelines and configs utilized to ingress controller to ahead site visitors to single purposes, through paths or through area title 
kubectl get ingress
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kubectl create ingress <ingress-name> --rule="host/path=service-name:port"
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kubectl create ingress world --rule=world.universe.mine/europe*=europe:80 --rule=world.universe.mine/asia*=asia:80  --class=nginx -n world
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Community Insurance policies

kubectl get netpol
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Storage

  • Volumes

  • Persistent Volumes

  • Persistent Quantity Declare

  kubeclt delete pvc <pvc-claim>
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Authentication

All consumer entry is managed by the api server

We are able to retailer consumer credentials as:

    # Add this to kubeapi server service or pod definition file
    --basic-auth-file=user-credentials.csv
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    curl -v -k <api-url> -u "consumer:password"
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   # Add this to kubeapi server service or pod definition file
   --token-auth-file=user-credentials.csv
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    curl -v -k <api-url> --header "Authorization: Bearer <TOKEN>"
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We are able to use kubeconfig to handle which clusters we will entry

kubectl config view --kubeconfig=my-custom-file
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kubectl config use-context developer-development-playground
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kubectl config get-context developer-development-playground
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Authorization

Authorization modes:

  • Node authorizer -> handles node requests (consumer ought to have title prefixed system node)
  • Attribute primarily based authotization -> Assosiate customers/group of customers with a set of permissions(troublesome to handle)
  • Function bases entry management -> We outline roles and affiliate customers with particular roles
  • Webhook -> Outsource authorization to third social gathering instruments
  • AlwaysAllow -> Permits all requests with out doing authorization checks (default)
  • AlwaysDeny -> Denys all requests

On kubeapiserver, we specify modes to make use of --authorization-mode=Node,RBAC,Webhook

Function primarily based entry management:

kubectl get roles
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kubectl create function take a look at --verb=listing,create --resource=pods
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kubectl describe function <role-name>
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kubectl get rolebindings
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kubectl create rolebinding test-rb --role=take a look at --user=user1 --group=group1
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kubectl describe rolebindings <rolebindings-name>
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kubectl auth can-i create deploy
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kubectl auth can-i create deploy --as dev-user --namespace dev
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kubectl api-resources --namespaced=false
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We are able to create roles scoped on clusters. We are able to additionally create cluster roles on namespace scoped sources

Cluster Function primarily based entry management:

kubectl create clusterrole take a look at --verb=* --resource=*
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kubectl create clusterrolebinding test-rb --clusterrole=take a look at --user=consumer --group=group
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Admission Controllers

  • Implement safety measures to implement how a cluster is used.
  • It may validate, change or reject requests from customers
  • It may additionally carry out operations within the backend 
kube-apiserver -h | grep enable-admission-plugins
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On kubeapiserver, to allow an admission controller we replace the --enable-admission-plugins=NodeRestriction,NamespaceLifecycle
On kubeapiserver, to disable an admission controller we replace the --disable-admission-plugins=DefaultStorageClass

We are able to create {custom} admission contollers:

  • We use the Mutating and Validating webhooks that we configure to a server internet hosting our admission webhook service.
    If a request is made, it goes sends an admission evaluation object to admission webhook server that responds whith an admission evaluation object of whether or not the result’s allowed or not

  • We then deploy our admission webhook server

  • We then configure to succeed in out to the service and validate or mutate requests by making a validating configuration object



Customized Useful resource Definition

An extension of the Kubernetes API that is not obtainable within the Kubernetes set up



Customized Controller

Course of or code working in a loop and monitoring the kubernetes cluster and listening to occasions of particular objects

We construct the {custom} controller then present kubeconfig file the controller would want to authenticate to the kubernetes api

Thanks!

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