Kubernetes Basics - ConfigMap Example

ConfigMap Example

Download the YAML configuration files for the ConfigMap example

Download cm.yaml Download pod.yaml

Create the ConfigMap

kubectl apply -f cm.yaml

Applies the configuration from the YAML file to create the ConfigMap.

Get the ConfigMap info

kubectl get cm

kubectl describe configmap cm-example

Lists all ConfigMaps and shows detailed information about the cm-example ConfigMap.

Output ConfigMap in YAML format

kubectl get configmap cm-example -o YAML

Outputs the ConfigMap information in YAML format.

Deploy the pod

kubectl apply -f pod.yaml

Creates a pod that uses the ConfigMap data as environment variables.

Connect to the Busybox

kubectl exec mybox -it -- /bin/sh

Opens a shell inside the running Busybox container.

Display the CITY env variable

echo $CITY

exit

Displays the CITY environment variable value from the ConfigMap, then exits the container.

Cleanup

kubectl delete -f cm.yaml

kubectl delete -f pod.yaml --grace-period=0 --force

Deletes the ConfigMap and pod resources.

YAML Configuration Files

cm.yaml

apiVersion: v1
kind: ConfigMap
metadata:
  name: cm-example
data:
  state: Michigan
  city: Ann Arbor

ConfigMap Explanation:

ConfigMap Structure:

apiVersion: v1 → Specifies the Kubernetes API version
kind: ConfigMap → Defines this as a ConfigMap resource
metadata.name: cm-example → Names the ConfigMap "cm-example"

Data Section:

state: Michigan → Key-value pair for state information
city: Ann Arbor → Key-value pair for city information

How It Works:

ConfigMaps allow you to decouple configuration artifacts from container images. This ConfigMap stores two key-value pairs that can be consumed by pods as environment variables, command-line arguments, or configuration files.

pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: mybox
spec:
  restartPolicy: Always
  containers:
  - name: mybox
    image: busybox
    resources:
      requests:
        cpu: 100m
        memory: 128Mi
      limits:
        cpu: 250m
        memory: 256Mi    
    command:
      - sleep
      - "3600"
    env:
      - name: CITY
        valueFrom:
          configMapKeyRef:
            name: cm-example
            key: city

Pod Explanation:

Pod Structure:

apiVersion: v1 → Specifies the Kubernetes API version
kind: Pod → Defines this as a Pod resource
metadata.name: mybox → Names the pod "mybox"
restartPolicy: Always → Specifies restart policy

Container Configuration:

image: busybox → Uses the lightweight BusyBox image
resources → Defines CPU and memory requests/limits
command: ["sleep", "3600"] → Runs sleep command to keep container alive

Environment Variables:

env → Defines environment variables for the container
name: CITY → Names the environment variable "CITY"
valueFrom.configMapKeyRef → References a value from a ConfigMap
name: cm-example → References the ConfigMap named "cm-example"
key: city → Uses the value of the "city" key from the ConfigMap

How It Works:

This pod creates a BusyBox container that sleeps for 3600 seconds (1 hour). The container has an environment variable named CITY that gets its value from the "city" key in the "cm-example" ConfigMap. When you exec into the container and run "echo $CITY", it will display "Ann Arbor".