40 Days Of Kubernetes (19/40)

#kubernetes #40daysofkubernetes

Day 19/40

Kubernetes configmap and secret

Video Link
@piyushsachdeva
Git Repository
My Git Repo

We will look at configMap an secret in Kubernetes concepts in this section.
It's not a best practice to save env, key and value in yaml file of a workload such as pod yaml file.

Kubernetes Secrets and ConfigMaps separate the configuration of individual container instances from the container image, reducing overhead and adding flexibility.

Kubernetes has two types of objects that can inject configuration data into a container when it starts up.

source

Demo

Let's see the below yaml file, there's an env with name FIRSTNAME and value is Piyush:

apiVersion: v1
kind: Pod
metadata:
  name: myapp-pod
  labels:
    app.kubernetes.io/name: MyApp
spec:
  containers:
  - name: myapp-container
    image: busybox:1.28
    env:
    - name: FIRSTNAME
      value: "Piyush"
    command: ['sh', '-c', 'echo The app is running! && sleep 3600']

Let's run and check the env inside the pod:

root@localhost:~# kubectl apply -f day19-configmap.yaml
pod/myapp-pod created
root@localhost:~# kubectl get pod
NAME        READY   STATUS    RESTARTS   AGE
myapp-pod   1/1     Running   0          8s
root@localhost:~# kubectl exec -it myapp-pod -- sh
/ # echo $FIRSTNAME
Piyush

Now, we are going to do it with different ways as mentioned, configMap.

Imperative:

root@localhost:~# kubectl create cm app-cm --from-literal=FIRSTNAME=Piyush --from-literal=NEXT=Sina
configmap/app-cm created
root@localhost:~# kubectl get cm
NAME               DATA   AGE
app-cm             2      5s
kube-root-ca.crt   1      16d
root@localhost:~# kubectl describe cm app-cm
Name:         app-cm
Namespace:    default
Labels:       <none>
Annotations:  <none>

Data
====
FIRSTNAME:
----
Piyush
NEXT:
----
Sina

BinaryData
====

Events:  <none>

Then we need to inject to yaml file of our pod, and define specific block for each environment variable:

apiVersion: v1
kind: Pod
metadata:
  name: myapp-pod
  labels:
    app.kubernetes.io/name: MyApp
spec:
  containers:
  - name: myapp-container
    image: busybox:1.28
    env:
    - name: firstName
      valueFrom:
        configMapKeyRef:
          name: app-cm
          key: FIRSTNAME
    - name: next
      valueFrom:
        configMapKeyRef:
          name: app-cm
          key: NEXT
    command: ['sh', '-c', 'echo The app is running! && sleep 3600']

Let's run and check:

root@localhost:~# kubectl apply -f day19-configmap.yaml
pod/myapp-pod created
root@localhost:~# kubectl get pod
NAME        READY   STATUS    RESTARTS   AGE
myapp-pod   1/1     Running   0          36s
root@localhost:~# kubectl exec -it myapp-pod -- sh
/ # echo $firstName
Piyush
/ # echo $next
Sina
/ #

root@localhost:~# kubectl describe po/myapp-pod
Name:             myapp-pod
...
    Environment:
      firstName:  <set to the key 'FIRSTNAME' of config map 'app-cm'>  Optional: false
      next:       <set to the key 'NEXT' of config map 'app-cm'>       Optional: false
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from kube-api-
...

Declarative: Let's create yaml file from dry-run option:

root@localhost:~# kubectl create cm app-cm --from-literal=FIRSTNAME=Piyush --from-literal=NEXT=Sina --dry-run=client -o yaml > day19-cm.yaml

The yaml file would be below:

apiVersion: v1
data:
  FIRSTNAME: Piyush
  NEXT: Sina
kind: ConfigMap
metadata:
  creationTimestamp: null
  name: app-cm

Sample for cm:

apiVersion: v1
data:
  FIRSTNAME: Piyush
  NEXT: Sina
kind: ConfigMap
metadata:
  creationTimestamp: null
  name: app-cm

Sample for pod:

apiVersion: v1
kind: Pod
metadata:
  name: dapi-test-pod
spec:
  containers:
    - name: test-container
      image: registry.k8s.io/busybox
      command: [ "/bin/sh", "-c", "env" ]
      envFrom:
      - configMapRef:
          name: app-cm
  restartPolicy: Never

Let's check:

root@localhost:~# kubectl get cm,pod
NAME                         DATA   AGE
configmap/app-cm             2      5m53s
configmap/kube-root-ca.crt   1      16d

NAME                READY   STATUS      RESTARTS   AGE
pod/dapi-test-pod   0/1     Completed   0          4m15s

root@localhost:~# kubectl describe pod dapi-test-pod
Name:             dapi-test-pod
...
    Environment Variables from:
      app-cm      ConfigMap  Optional: false

...