• Centrally managed configuration data that can be passed to the containers as environment variables (key-value pairs).
• Storing config data along with the pod/deployment definition file is not a good idea because as the application grows, managing them would become difficult.
• Should be used to store parameters that are not secrets

<aside> ⚠️ The data stored in the ConfigMap, when the container (pod) is created, is used to set the environment variables. If the ConfigMap gets updated later, the pod will continue to use the old values. We need to re-create the pods by performing a rollout (k rollout restart deployment <deployment-name>) on the deployment to make the new pods use the new data.

</aside>

ConfigMap definition file

apiVersion: v1
kind: ConfigMap
metadata:
	name: app-config
data:
	USERNAME: arkalim
	PASSWORD: 12345

Using file as a ConfigMap:

apiVersion: v1
kind: ConfigMap
metadata:
  name: rho-pacs-config
  namespace: 16bit
data:
  orthanc.json: |
    {
      /**
      * General configuration of Orthanc
      **/
    }

Using ConfigMap in Pods

• Passing the entire ConfigMap of key-value pairs to ENV

  apiVersion: v1
  kind: Pod
  metadata:
    labels:
      name: app
  spec:
    containers:
  	  - name: nginx
  	    image: nginx
  			envFrom:
  				- configMapRef:
  					  name: app-config
  

• Passing a single key-value pair from the ConfigMap to ENV

  apiVersion: v1
  kind: Pod
  metadata:
    labels:
      name: app
  spec:
    containers:
  	  - name: nginx
  	    image: nginx
  			env:
  				- name: USERNAME
  					valueFrom:
  						configMapKeyRef:
  							name: app-config
  							key: USERNAME
  

• Passing a config file as ConfigMap (eg. nginx.conf) by mounting the ConfigMap as a volume

  apiVersion: v1
  kind: Pod
  metadata:
    labels:
      name: app
  spec:
    containers:
  	  - name: nginx
  	    image: nginx
  			volumeMounts:
          - name: nginx-config-volume
            mountPath: /etc/nginx/conf.d/
    volumes:
      - name: nginx-config-volume
        configMap:
          name: nginx-config