This article gives a brief idea on ConfigMaps and secrets in K8s.

ConfigMaps can be used to provide configuration data in the form of key value pairs.

why we use ConfigMaps ?
when we have a lot of pod definition file, it is difficult to manage the environment data stored in it. we can place this information out of pod definition file and manage it centrally with configuration map.

abiconfig.txt

parameter1 = value1
parameter2 = value2

How can you use the ConfigMap ?

There are three main ways to use a ConfigMap
Filesystem: You can mount a ConfigMap into a Pod. A file is created for each entry based on the key name. The contents of that file are set to the value.
Environment variable: A ConfigMap can be used to dynamically set the value of an environment variable.
Command-line argument: Kubernetes supports dynamically creating the command line for a container based on ConfigMap values

 kubectl create configmap abiconfig \
 --from-file=abiconfig.txt \
 --from-literal=extra-param=prod \ # This has highest priority
 --from-literal=another-param=k8s

The exact we can do with Declarative approach through an manifest file.

apiVersion: v1
kind: ConfigMap
metadata:
   name: abiconfig
   namespace: default
data:
 another-param: k8s
 extra-param: prod
 my-config.txt: |
    parameter1 = value1
    parameter2 = value2

commands for ConfigMap:

kubectl get configmaps
kubectl describe configmaps

apiVersion: v1 # String 
kind: Pod # String 
metadata: # Dictionary 
  name: myapp1-pod 
  labels: # Dictionary 
    app: myapp1 # Key value pairs 
spec: 
  containers: # List 
    - name: myapp1 
      image: myimage/kubenginx 
      ports: 
        - containerPort: 80
      env:
        - name: ANOTHER_PARAM
          valueFrom:
             configMapKeyRef:
               name: abiconfig
               key: another-param
        - name: EXTRA_PARAM
          valueFrom:
            configMapKeyRef:
              name: abiconfig
              key: extra-param

Kubernetes secrets

A Secret is an object that contains a small amount of sensitive data such as a password, a token, or a key. Secrets are similar to ConfigMaps but are specifically intended to hold confidential data. Secrets hold one or more data elements as a collection of key/value pairs. By default, Kubernetes secrets are stored in plain text in the etcd storage for the cluster. anyone who has cluster administration rights in your cluster will be able to read all of the secrets in the cluster.

key notes

In order to safely use Secrets, take at least the following steps:

1. Enable Encryption at Rest for Secrets.

2. Enable or configure RBAC rules with least-privilege access to Secrets.

3. Restrict Secret access to specific containers.

4. Consider using external Secret store providers.