d.configuration.md

Configuration (18%)

ConfigMaps

kubernetes.io > Documentation > Tasks > Configure Pods and Containers > Configure a Pod to Use a ConfigMap

Create a configmap named config with values foo=lala,foo2=lolo

show

kubectl create configmap config --from-literal=foo=lala --from-literal=foo2=lolo

Display its values

show

kubectl get cm config -o yaml --export
# or
kubectl describe cm config

Create and display a configmap from a file

Create the file with

echo -e "foo3=lili\nfoo4=lele" > config.txt

show

kubectl create cm configmap2 --from-file=config.txt
kubectl get cm configmap2 -o yaml --export

Create and display a configmap from a .env file

Create the file with the command

echo -e "var1=val1\n# this is a comment\n\nvar2=val2\n#anothercomment" > config.env

show

kubectl create cm configmap3 --from-env-file=config.env
kubectl get cm configmap3 -o yaml --export

Create and display a configmap from a file, giving the key 'special'

Create the file with

echo -e "var3=val3\nvar4=val4" > config4.txt

show

kubectl create cm configmap4 --from-file=special=config4.txt
kubectl describe cm configmap4
kubectl get cm configmap4 -o yaml --export

Create a configMap called 'options' with the value var5=val5. Create a new nginx pod that loads the value from variable 'var5' in an env variable called 'option'

show

kubectl create cm options --from-literal=var5=val5
kubectl run nginx --image=nginx --restart=Never --dry-run -o yaml > pod.yaml
vi pod.yaml

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: nginx
  name: nginx
spec:
  containers:
  - image: nginx
    imagePullPolicy: IfNotPresent
    name: nginx
    resources: {}
    env:
    - name: option # name of the env variable
      valueFrom:
        configMapKeyRef:
          name: options # name of config map
          key: var5 # name of the entity in config map
  dnsPolicy: ClusterFirst
  restartPolicy: Never
status: {}

kubectl create -f pod.yaml
kubectl exec -it nginx -- env | grep option # will show 'option=val5'

Create a configMap 'anotherone' with values 'var6=val6', 'var7=val7'. Load this configMap as env variables into a new nginx pod

show

kubectl create configmap anotherone --from-literal=var6=val6 --from-literal=var7=val7
kubectl run --restart=Never nginx --image=nginx -o yaml --dry-run > pod.yaml
vi pod.yaml

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: nginx
  name: nginx
spec:
  containers:
  - image: nginx
    imagePullPolicy: IfNotPresent
    name: nginx
    resources: {}
    envFrom: # different than previous one, that was 'env'
    - configMapRef: # different from the previous one, was 'configMapKeyRef'
        name: anotherone # the name of the config map
  dnsPolicy: ClusterFirst
  restartPolicy: Never
status: {}

kubectl create -f pod.yaml
kubectl exec -it nginx -- env 

Create a configMap 'cmvolume' with values 'var8=val8', 'var9=val9'. Load this as a volume inside an nginx pod on path '/etc/lala'. Create the pod and 'ls' into the '/etc/lala' directory.

show

kubectl create configmap cmvolume --from-literal=var8=val8 --from-literal=var9=val9
kubectl run nginx --image=nginx --restart=Never -o yaml --dry-run > pod.yaml
vi pod.yaml

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: nginx
  name: nginx
spec:
  volumes: # add a volumes list
  - name: myvolume # just a name, you'll reference this in the pods
    configMap:
      name: cmvolume # name of your configmap
  containers:
  - image: nginx
    imagePullPolicy: IfNotPresent
    name: nginx
    resources: {}
    volumeMounts: # your volume mounts are listed here
    - name: myvolume # the name that you specified in pod.spec.volumes.name
      mountPath: /etc/lala # the path inside your container
  dnsPolicy: ClusterFirst
  restartPolicy: Never
status: {}

kubectl exec -it nginx -- /bin/sh
cd /etc/lala
ls # will show var8 var9
cat var8 # will show val8

SecurityContext

kubernetes.io > Documentation > Tasks > Configure Pods and Containers > Configure a Security Context for a Pod or Container

Create the YAML for an nginx pod that runs with the UID 101. No need to create the pod

show

kubectl run nginx --image=nginx --restart=Never --dry-run -o yaml > pod.yaml
vi pod.yaml

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: nginx
  name: nginx
spec:
  securityContext: # insert this line
    runAsUser: 101 # UID for the user
  containers:
  - image: nginx
    imagePullPolicy: IfNotPresent
    name: nginx
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Never
status: {}

Create the YAML for an nginx pod that has the capabilities "NET_ADMIN", "SYS_TIME" added on its single container

show

kubectl run nginx --image=nginx --restart=Never --dry-run -o yaml > pod.yaml
vi pod.yaml

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: nginx
  name: nginx
spec:
  containers:
  - image: nginx
    imagePullPolicy: IfNotPresent
    name: nginx
    securityContext: # insert this line
      capabilities: # and this
        add: ["NET_ADMIN", "SYS_TIME"] # this as well
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Never
status: {}

Requests and limits

kubernetes.io > Documentation > Tasks > Configure Pods and Containers > Assign CPU Resources to Containers and Pods

Create an nginx pod with requests cpu=100m,memory=256Mi and limits cpu=200m,memory=512Mi

show

kubectl run nginx --image=nginx --restart=Never --requests='cpu=100m,memory=256Mi' --limits='cpu=200m,memory=512Mi'

Secrets

kubernetes.io > Documentation > Concepts > Configuration > Secrets

kubernetes.io > Documentation > Tasks > Inject Data Into Applications > Distribute Credentials Securely Using Secrets

Create a secret called mysecret with the values password=mypass

show

kubectl create secret generic mysecret --from-literal=password=mypass

Create a secret called mysecret2 that gets key/value from a file

Create a file called username with the value admin:

echo admin > username

show

kubectl create secret generic mysecret2 --from-file=username

Get the value of mysecret2

show

kubectl get secret mysecret2 -o yaml --export
echo YWRtaW4K | base64 -d # shows 'admin'

Alternative:

kubectl get secret mysecret2 -o jsonpath='{.data.username}{"\n"}' | base64 -d  # on MAC it is -D

Create an nginx pod that mounts the secret mysecret2 in a volume on path /etc/foo

show

kubectl run nginx --image=nginx --restart=Never -o yaml --dry-run > pod.yaml
vi pod.yaml

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: nginx
  name: nginx
spec:
  volumes: # specify the volumes
  - name: foo # this name will be used for reference inside the container
    secret: # we want a secret
      secretName: mysecret2 # name of the secret - this must already exist on pod creation
  containers:
  - image: nginx
    imagePullPolicy: IfNotPresent
    name: nginx
    resources: {}
    volumeMounts: # our volume mounts
    - name: foo # name on pod.spec.volumes
      mountPath: /etc/foo #our mount path
  dnsPolicy: ClusterFirst
  restartPolicy: Never
status: {}

kubectl create -f pod.yaml
kubectl exec -it nginx /bin/bash
ls /etc/foo  # shows username
cat /etc/foo/username # shows admin

Delete the pod you just created and mount the variable 'username' from secret mysecret2 onto a new nginx pod in env variable called 'USERNAME'

show

kubectl delete po nginx
kubectl run nginx --image=nginx --restart=Never -o yaml --dry-run > pod.yaml
vi pod.yaml

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: nginx
  name: nginx
spec:
  containers:
  - image: nginx
    imagePullPolicy: IfNotPresent
    name: nginx
    resources: {}
    env: # our env variables
    - name: USERNAME # asked name
      valueFrom:
        secretKeyRef: # secret reference
          name: mysecret2 # our secret's name
          key: username # the key of the data in the secret
  dnsPolicy: ClusterFirst
  restartPolicy: Never
status: {}

kubectl create -f pod.yaml
kubectl exec -it nginx -- env | grep USERNAME | cut -d '=' -f 2 # will show 'admin'

ServiceAccounts

kubernetes.io > Documentation > Tasks > Configure Pods and Containers > Configure Service Accounts for Pods

See all the service accounts of the cluster in all namespaces

show

kubectl get sa --all-namespaces

Create a new serviceaccount called 'myuser'

show

kubectl create sa myuser

Alternatively:

# let's get a template easily
kubectl get sa default -o yaml --export > sa.yaml
vim sa.yaml

apiVersion: v1
kind: ServiceAccount
metadata:
  name: myuser

kubectl create -f sa.yaml

Create an nginx pod that uses 'myuser' as a service account

show

kubectl run nginx --image=nginx --restart=Never -o yaml --dry-run > pod.yaml
vi pod.yaml

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: nginx
  name: nginx
spec:
  serviceAccountName: myuser # we use pod.spec.serviceAccountName
  containers:
  - image: nginx
    imagePullPolicy: IfNotPresent
    name: nginx
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Never
status: {}

kubectl create -f pod.yaml
kubectl describe pod nginx # will see that a new secret called myuser-token-***** has been mounted

or you can add directly with kubectl run command:

kubectl run nginx --image=nginx --restart=Never --serviceaccount=myuser -o yaml --dry-run > pod.yaml
kubectl apply -f pod.yaml