apiVersion: v1
kind: ConfigMap
metadata:
  name: simple-config
  namespace: default
data:
  portNumber: "8080"
  name: Ricky
  settings.env: |
    someVariable=5
    anotherName=blah

Save the above YAML into a file called simple-config.yaml and create it by running kubectl apply -f simple-config.yaml.

To see the details of the ConfigMap you create, you can use the describe command:

$ kubectl describe cm simple-config
Name:         simple-config
Namespace:    default
Labels:       <none>
Annotations:
Data
====
name:
----
Ricky
portNumber:
----
8080
settings.env:
----
someVariable=5
anotherName=blah

Events:  <none>

For Pod to use the values from the ConfigMap, both Pod and ConfigMap need to reside in the same namespace. You can mount a ConfigMap to your Pod and use the values in one of the following ways:

• As command-line arguments
• As environment variables
• As a file in a read-only-volume
• Through Kubernetes API that reads the ConfigMap

Let's create a Pod and show how to consume the values from a ConfigMap.

apiVersion: v1
kind: Pod
metadata:
  name: config-pod
  labels:
    app.kubernetes.io/name: config-pod
spec:
  containers:
    - name: config
      image: busybox
      command: ["sh", "-c", "sleep 3600"]
      env:
        - name: FIRST_NAME
          valueFrom:
            configMapKeyRef:
              name: simple-config
              key: name
        - name: PORT_NUMBER
          valueFrom:
            configMapKeyRef:
              name: simple-config
              key: portNumber

We are using the valueFrom and configMapKeyRef to specify where the value for the environment variable is coming from. The environment variable name (e.g. FIRST_NAME) is and can be different from the key name stored in the ConfigMap (e.g. name or portNumber).

Save the above YAML in config-pod-1.yaml and create the Pod with kubectl apply -f config-pod-1.yaml. Once the Pod is running, let's get the terminal inside the container and look at the environment variables:

$ kubectl exec -it config-pod -- /bin/sh
/ # env
KUBERNETES_PORT=tcp://10.96.0.1:443
KUBERNETES_SERVICE_PORT=443
HOSTNAME=config-pod
SHLVL=1
HOME=/root
PORT_NUMBER=8080
TERM=xterm
KUBERNETES_PORT_443_TCP_ADDR=10.96.0.1
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
KUBERNETES_PORT_443_TCP_PORT=443
KUBERNETES_PORT_443_TCP_PROTO=tcp
FIRST_NAME=Ricky
KUBERNETES_SERVICE_PORT_HTTPS=443
KUBERNETES_PORT_443_TCP=tcp://10.96.0.1:443
KUBERNETES_SERVICE_HOST=10.96.0.1
PWD=/

Notice the PORT_NUMBER and FIRST_NAME environment variables values are coming from the ConfigMap.

How about the values under the settings.env key? Let's mount that as a file inside the Pod.

Here's the updated YAML for the config-pod: