Env & ConfigMaps in Kubernetes

In modern cloud-native applications, managing configuration and sensitive data efficiently and securely is essential. Kubernetes addresses this need with ConfigMaps. ConfigMaps store non-confidential configuration data, enabling dynamic updates and easy application portability. By separating configuration and sensitive data from application code, Kubernetes enhances security, flexibility, and adherence to best practices. Let's understand these concepts better through hands-on examples.

ConfigMaps

ConfigMap is a Kubernetes resource used to store non-confidential data in key-value pairs. It allows you to decouple configuration artifacts from image content to keep containerized applications portable.

Example

Create a Pod with an Environment Variable

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

The above YAML file (pod.yaml) creates a pod with the BusyBox image. It sets an environment variable FIRSTNAME within the container. Apply this file and execute into the container to check the environment variable:

  kubectl apply -f pod.yaml
  kubectl exec -it myapp -- sh
  echo $FIRSTNAME  # Output will be "harshit"

Create a ConfigMap

Next, we'll create a ConfigMap to store these values and inject it into the Pod.

  kubectl create configmap app-cm --from-literal=firstname=harshit --from-literal=lastname=sahu

Inject ConfigMap into a Pod

Now, modify the Pod definition to use the ConfigMap:

 apiVersion: v1
 kind: Pod
 metadata:
   name: myapp
   labels:
     name: myapp-pod
 spec:
   containers:
     - name: myapp-container
       image: busybox:1.28
       command: ["sh", "-c", "echo The app is running! && sleep 3600"]
       env:
         - name: FIRSTNAME
           valueFrom:
             configMapKeyRef:
               name: app-cm
               key: firstname

Apply this YAML file:

  kubectl apply -f pod.yaml

When you describe the Pod, you will see that the FIRSTNAME environment variable is now sourced from the ConfigMap.

Imperative ConfigMap Creation with file

 kubectl create configmap app-cm --from-file=map.configure

Declarative ConfigMap Creation

If you have many key-value pairs, creating a ConfigMap from the command line can be cumbersome. Instead, you can create it declaratively using a YAML file. You can generate this file with an imperative command:

  kubectl create configmap app-cm --from-literal=firstname=harshit --from-literal=lastname=sahu --dry-run=client -o yaml > cm.yaml

This will generate a cm.yaml file:

  apiVersion: v1
  kind: ConfigMap
  metadata:
    name: app-cm
  data:
    firstname: harshit
    lastname: sahu

Apply this YAML file:

  kubectl apply -f cm.yaml

ConfigMaps can also be used by mounting them as volumes, which we will cover in future posts in this series. You can also learn more about ConfigMaps from the official documentation.

Env & ConfigMaps in Kubernetes - CKA

ConfigMaps

Example