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2-configuration.md

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Configuration (18%)

Configuring a Pod to Use a ConfigMap

  1. Create a new file named config.txt with the following environment variables as key/value pairs on each line.
  • DB_URL equates to localhost:3306
  • DB_USERNAME equates to postgres
  1. Create a new ConfigMap named db-config from that file.
  2. Create a Pod named backend that uses the environment variables from the ConfigMap and runs the container with the image nginx.
  3. Shell into the Pod and print out the created environment variables. You should find DB_URL and DB_USERNAME with their appropriate values.
Show Solution

Create the environment variables in the text file.

$ echo -e "DB_URL=localhost:3306\nDB_USERNAME=postgres" > config.txt

Create the ConfigMap and point to the text file upon creation.

$ kubectl create configmap db-config --from-env-file=config.txt
configmap/db-config created
$ kubectl run backend --image=nginx --restart=Never -o yaml --dry-run > pod.yaml

The final YAML file should look similar to the following code snippet.

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: backend
  name: backend
spec:
  containers:
  - image: nginx
    name: backend
    envFrom:
      - configMapRef:
          name: db-config
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Never
status: {}

Create the Pod by pointing the create command to the YAML file.

$ kubectl create -f pod.yaml

Log into the Pod and run the env command.

$ kubectl exec backend -it -- /bin/sh
/ # env
DB_URL=localhost:3306
DB_USERNAME=postgres
...
/ # exit

Configuring a Pod to Use a Secret

  1. Create a new Secret named db-credentials with the key/value pair db-password=passwd.
  2. Create a Pod named backend that defines uses the Secret as environment variable named DB_PASSWORD and runs the container with the image nginx.
  3. Shell into the Pod and print out the created environment variables. You should find DB_PASSWORD variable.
Show Solution

It's easy to create the secret from the command line. Furthermore, execute the run command to generate the YAML file for the Pod.

$ kubectl create secret generic db-credentials --from-literal=db-password=passwd
secret/db-credentials created
$ kubectl get secrets
NAME              TYPE      DATA   AGE
db-credentials    Opaque    1      26s
$ kubectl run backend --image=nginx --restart=Never -o yaml --dry-run > pod.yaml

Edit the YAML file and create an environment that reads the relevant key from the secret.

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: backend
  name: backend
spec:
  containers:
  - image: nginx
    name: backend
    env:
      - name: DB_PASSWORD
        valueFrom:
          secretKeyRef:
            name: db-credentials
            key: db-password
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Never
status: {}

Create the Pod by pointing the create command to the YAML file.

$ kubectl create -f pod.yaml

You can find the environment variable by shelling into the container and running the env command.

$ kubectl exec -it backend -- /bin/sh
/ # env
DB_PASSWORD=passwd
/ # exit

Creating a Security Context for a Pod

  1. Create a Pod named secured that uses the image nginx for a single container. Mount an emptyDir volume to the directory /data/app.
  2. Files created on the volume should use the filesystem group ID 3000.
  3. Get a shell to the running container and create a new file named logs.txt in the directory /data/app. List the contents of the directory and write them down.
Show Solution

Start by creating the Pod definition as YAML file.

$ kubectl run secured --image=nginx --restart=Never -o yaml --dry-run > secured.yaml

Edit the YAML file, add a volume and a volume mount. Add a security context with the relevant group ID.

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: secured
  name: secured
spec:
  securityContext:
    fsGroup: 3000
  containers:
  - image: nginx
    name: secured
    volumeMounts:
    - name: data-vol
      mountPath: /data/app
    resources: {}
  volumes:
  - name: data-vol
    emptyDir: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Never
status: {}

Create the Pod and log into the container. Create the file in the directory of the volume mount. The group ID should be 3000 as defined by the security context.

$ kubectl create -f secured.yaml
pod/secured created
$ kubectl exec -it secured -- sh
/ # cd /data/app
/ # touch logs.txt
/ # ls -l
-rw-r--r-- 1 root 3000 0 Mar 11 15:56 logs.txt
/ # exit

Defining a Pod’s Resource Requirements

Create a resource quota named apps under the namespace rq-demo using the following YAML definition in the file rq.yaml.

apiVersion: v1
kind: ResourceQuota
metadata:
  name: app
spec:
  hard:
    pods: "2"
    requests.cpu: "2"
    requests.memory: 500m
  1. Create a new Pod that exceeds the limits of the resource quota requirements. Write down the error message.
  2. Change the request limits to fulfill the requirements to ensure that the Pod could be created successfully. Write down the output of the command that renders the used amount of resources for the namespace.
Show Solution

First create the namespace and the resource quota in the namespace.

$ kubectl create namespace rq-demo
$ kubectl create -f rq.yaml --namespace=rq-demo
resourcequota/app created
$ kubectl describe quota --namespace=rq-demo
Name:            app
Namespace:       rq-demo
Resource         Used  Hard
--------         ----  ----
pods             0     2
requests.cpu     0     2
requests.memory  0     500m

Next, create the YAML file named pod.yaml with more requested memory than available in the quota.

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: mypod
  name: mypod
spec:
  containers:
  - image: nginx
    name: mypod
    resources:
      requests:
        memory: "1G"
        cpu: "400m"
  dnsPolicy: ClusterFirst
  restartPolicy: Never
status: {}

Create the Pod and observe the error message.

$ kubectl create -f pod.yaml --namespace=rq-demo
Error from server (Forbidden): error when creating "pod.yaml": pods "mypod" is forbidden: exceeded quota: app, requested: requests.memory=1G, used: requests.memory=0, limited: requests.memory=500m

Lower the memory settings to less than 500m (e.g. 200m) and create the Pod.

$ kubectl create -f pod.yaml --namespace=rq-demo
pod/mypod created
$ kubectl describe quota --namespace=rq-demo
Name:            app
Namespace:       rq-demo
Resource         Used  Hard
--------         ----  ----
pods             1     2
requests.cpu     400m  2
requests.memory  200m  500m

Using a Service Account

  1. Create a new service account named backend-team.
  2. Print out the token for the service account in YAML format.
  3. Create a Pod named backend that uses the image nginx and the identity backend-team for running processes.
  4. Get a shell to the running container and print out the token of the service account.
Show Solution

First, create the service acccount and inspect it.

$ kubectl create serviceaccount backend-team
serviceaccount/backend-team created
$ kubectl get serviceaccount backend-team -o yaml --export
apiVersion: v1
kind: ServiceAccount
metadata:
  creationTimestamp: 2019-05-09T22:43:54Z
  name: backend-team
  namespace: default
  resourceVersion: "1888067"
  selfLink: /api/v1/namespaces/default/serviceaccounts/backend-team
  uid: ecd3b7ea-72ab-11e9-96c5-025000000001
secrets:
- name: backend-team-token-hskch

Next, you can create a new Pod and assign the service account to it.

$ kubectl run backend --image=nginx --restart=Never --serviceaccount=backend-team

You can print out the token from the volume source at /var/run/secrets/kubernetes.io/serviceaccount.

$ kubectl exec -it backend -- /bin/sh
/ # cat /var/run/secrets/kubernetes.io/serviceaccount/token
eyJhbGciOiJSUzI1NiIsImtpZCI6IiJ9.eyJpc3MiOiJrdWJlcm5ldGVzL3NlcnZpY2VhY2NvdW50Iiwia3ViZXJuZXRlcy5pby9zZXJ2aWNlYWNjb3VudC9uYW1lc3BhY2UiOiJkZWZhdWx0Iiwia3ViZXJuZXRlcy5pby9zZXJ2aWNlYWNjb3VudC9zZWNyZXQubmFtZSI6ImJhY2tlbmQtdGVhbS10b2tlbi1kbTJmZCIsImt1YmVybmV0ZXMuaW8vc2VydmljZWFjY291bnQvc2VydmljZS1hY2NvdW50Lm5hbWUiOiJiYWNrZW5kLXRlYW0iLCJrdWJlcm5ldGVzLmlvL3NlcnZpY2VhY2NvdW50L3NlcnZpY2UtYWNjb3VudC51aWQiOiIxNzM0MzVjMS00NDJmLTExZTktOGRjMy0wMjUwMDAwMDAwMDEiLCJzdWIiOiJzeXN0ZW06c2VydmljZWFjY291bnQ6ZGVmYXVsdDpiYWNrZW5kLXRlYW0ifQ.DjWUxEMNUmQVoXd4b-eIjxboj3w3k7hS5hfV8mm8eoEPz3HJJMgjIpAaurcvo1pp2Ggpd1kIhQvfRqI6-u57f80N5UqXt_qATJfonat2NNXX8pXmFNoPig9LB-pbo8TN_pYGWNworXsxmK9w6V9eaRosIinRp0u-cvijQbsBw3lxWgGo9S4G-7f19mMKN1Pg2xS2J6fKX9IKvhHrUkM91nwcwmsO0use5B4TGbuRa9METiGsfEpegvzMPBbPl0B_T1ANH_pck0LFNtvKe0g1v5zpKx2lRF9WdFAqPsG7BJ1dEH88JtBHzD59OhxIPqtyT4sXKjACBN_ka5ZADMzPJg