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In this lab, you’ll learn how to manage environment variables in a Kubernetes pod and update them using both direct modifications and ConfigMaps. Follow along to understand how to check running pods, update environment variables, and integrate ConfigMaps for dynamic configuration.

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Checking the Running Pod

First, check how many pods are currently running. In this example, we’re working with a single pod named “webapp-color”: 
k get pods
Output: 
NAME            READY   STATUS    RESTARTS   AGE
webapp-color    1/1     Running   0          16s
Next, inspect the pod details to identify the configured environment variables. Look for the APP_COLOR variable, which in this case is set to pink: 
Image ID: docker.io/kodekloud/webapp-color@sha256:99c3821ea49b89c7a22d3eebabab5c2e1ec651452e7675
Port: Host Port: <none>
State: Running
Started: Sat, 16 Apr 2022 22:49:49 +0000
Ready: True
Restart Count: 0
Environment:
  APP_COLOR: pink
...
When you access the web application via the provided link, you’ll notice that the background color is pink.

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Updating the Pod to Change the Environment Variable

To change the background color of the web application, update the APP_COLOR environment variable. Start by editing the pod manifest using: 
kubectl edit pod webapp-color
Pods are immutable, so while you can edit a pod’s manifest, the changes cannot be applied directly. Instead, save the modified manifest locally and force replace the pod.
Below is an excerpt from the downloaded manifest where the APP_COLOR value is updated to "green": 
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: "2022-04-16T22:49:43Z"
  labels:
    name: webapp-color
  name: webapp-color
  namespace: default
  resourceVersion: "874"
  uid: 4f24d49d-04cc-4617-88b0-8478ca19a203
spec:
  containers:
  - env:
    - name: APP_COLOR
      value: green
    image: kodekloud/webapp-color
    imagePullPolicy: Always
    name: webapp-color
    resources: {}
    terminationMessagePath: /dev/termination-log
    terminationMessagePolicy: File
    volumeMounts:
    - mountPath: /var/run/secrets/kubernetes.io/serviceaccount
      name: kube-api-access-2nbfl
      readOnly: true
  dnsPolicy: ClusterFirst
  enableServiceLinks: true
  nodeName: controlplane
  preemptionPolicy: PreemptLowerPriority
  priority: 0
  restartPolicy: Always
  schedulerName: default-scheduler
  securityContext: {}
  serviceAccount: default
  serviceAccountName: default
Save your changes. If you receive an error stating that editing pods is forbidden due to immutability, don’t worry—the manifest is stored (e.g., in /tmp/kubectl-edit-3135302771.yaml). Force replace the existing pod with the updated manifest: 
kubectl replace --force -f /tmp/kubectl-edit-3135302771.yaml
You should see the following confirmation: 
pod "webapp-color" deleted
pod/webapp-color replaced
After the pod is recreated, verify that the change has taken effect: 
kubectl describe pod webapp-color
The output will now reflect that the environment variable APP_COLOR is set to green, and the web application’s background should display green.

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Working with ConfigMaps

In addition to direct environment variable updates, Kubernetes supports managing configurations with ConfigMaps. This provides a dynamic way to update environment variables for your pods.

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Listing Existing ConfigMaps

To see the current ConfigMaps in the default namespace, run: 
kubectl get configmap
Output: 
NAME                     DATA   AGE
kube-root-ca.crt        1      16m
db-config               3      22s

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Inspecting a Specific ConfigMap

To check the database host specified in the db-config ConfigMap, describe it: 
kubectl describe cm db-config
The description will include: 
Name:         db-config
Namespace:    default
Labels:       <none>
Annotations:  <none>

Data
====
DB_HOST:       
SQL01.example.com
DB_NAME:       
SQL01
DB_PORT:      
3306

BinaryData
==========
Events: <none>
This shows that the DB_HOST is set to SQL01.example.com.

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Creating a New ConfigMap for the Web Application

For the web application pod, we want to use a ConfigMap to set the environment variable dynamically. Create a new ConfigMap that sets APP_COLOR to dark blue: 
kubectl create configmap webapp-config-map --from-literal=APP_COLOR="dark blue"
This command creates a ConfigMap named webapp-config-map containing the desired environment variable.

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Updating the Pod to Use the New ConfigMap

Next, update the pod manifest so that the web application retrieves its environment variables from the ConfigMap instead of a static declaration. Modify the manifest to remove the direct env key and add an envFrom reference: 
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: "2022-04-16T22:52:40Z"
  labels:
    name: webapp-color
  name: webapp-color
  namespace: default
  resourceVersion: "929"
  uid: f17244ec-f17f-4027-9f6c-58aa47f2cf03
spec:
  containers:
  - envFrom:
      - configMapRef:
          name: webapp-config-map
    image: kodekloud/webapp-color
    imagePullPolicy: Always
    name: webapp-color
    resources: {}
    terminationMessagePath: /dev/termination-log
    terminationMessagePolicy: File
    volumeMounts:
    - mountPath: /var/run/secrets/kubernetes.io/serviceaccount
      name: kube-api-access-2nbfl
      readOnly: true
  dnsPolicy: ClusterFirst
  enableServiceLinks: true
  nodeName: controlplane
  preemptionPolicy: PreemptLowerPriority
  priority: 0
  restartPolicy: Always
  schedulerName: default-scheduler
  securityContext: {}
  serviceAccount: default
  serviceAccountName: default
Save your updated manifest and force replace the pod by running: 
kubectl replace --force -f /tmp/kubectl-edit-192529677.yaml
You will see confirmation messages: 
pod "webapp-color" deleted
pod/webapp-color replaced
Finally, verify the update: 
kubectl describe pod webapp-color
The pod description now shows that it sources its APP_COLOR environment variable from the webapp-config-map ConfigMap. When you access the web application, the background color will have changed to dark blue.
In this lab, you learned how to update environment variables both directly in a pod manifest and dynamically using ConfigMaps. These skills are essential for managing application configurations in Kubernetes.
Explore more about managing configurations in Kubernetes by visiting the Kubernetes Documentation.

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