# ConfigMaps explanation

By

Paul Tomoiu

●

In 

Kubernetes

●

Published 2022-12-03

This tutorial explains how a ConfigMaps could be used in Kubernetes.

ConfigMaps is an object used in Kubernetes to store data in key-value pairs. It's essentially a dictionary that contains configuration settings.

ConfigMaps in Kubernetes can be consumed in different ways:

• mounting it as a volume
• consumption via environment variables
• consumption via command-line arguments

ConfigMaps in Kubernetes can be created in different ways as well:

• from a file which keeps the key/value pairs
• from a ConfigMap object yaml file definition

We consider the following text file (properties.txt) :

database=oracle
host.name=linux1

We can create a ConfigMap named config-map-1-dev from this file, using the following command:

kubectl create configmap config-map-1-dev --from-file properties.txt

If we want to view the data in a ConfigMap via console output, we can use the following command:

kubectl describe configmaps config-map-1-dev

If we run this command we can see:

Name:         config-map-1-dev
Namespace:    default
Labels:       <none>
Annotations:  <none>

Data
====
properties.txt:
----
database=oracle\r
host.name=linux1

BinaryData
====

Events:  <none>

We can create a ConfigMap object yaml file as below and use it for creating another ConfigMap named config-map-2-dev.

Consider the following config-map-2-dev.yaml file:

apiVersion: v1
kind: ConfigMap
metadata:
 name: config-map-2-dev
data:
 # key/value format
 remote-database: "mongodb"
 remote-host: "linux2"
 
 # file-like keys
 application.properties: |
   server.port=8080
   service.maximum-instance=3   

We can create a ConfigMap named config-map-2-dev from this file, using the following command:

kubectl apply -f config-map-2-dev.yaml

If we need to see the ConfigMaps we have created, we can run the following command:

kubectl get configmaps

On my side, I can see the following result of the command:

NAME               DATA   AGE
config-map-1-dev   1      16m
config-map-2-dev   3      38s
kube-root-ca.crt   1      4d15h

Now we can create a pod to let it use some of these values defined in ConfigMaps:

apiVersion: v1
kind: Pod
metadata:
  name: nginx-pod
  labels:
    zone: dev
    version: v1
spec:
  containers:
  - name: nginx-c
    image: nginx:1.14.2
    ports:
    - containerPort: 8080

    env:
      - name: DATABASE_TYPE
        valueFrom:
          configMapKeyRef:
            name: config-map-1-dev
            key: database
      - name: SERVER_PORT
        valueFrom:
          configMapKeyRef:
            name: config-map-2-dev
            key: server.port

We can create the pod by running the following command:

kubectl apply -f configmaps-pod.yaml

At this point what is running into nginx-c container could have access to the DATABASE_TYPE and SERVER_PORT environment variable.

If we want to delete a ConfigMap we can run the following command:

kubectl delete configmap config-map-2-dev