Solution Env Variables Optional

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.

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.

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

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.

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.

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

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.

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.

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.

Explore more about managing configurations in Kubernetes by visiting the Kubernetes Documentation.