ConfigMaps in Kubernetes are used to decouple configuration artifacts from image content to keep containerized applications portable. They allow you to store configuration data in key-value pairs, which can be consumed by your applications as environment variables, command-line arguments, or configuration files.

• Key-Value Pairs: ConfigMaps store data as key-value pairs.
• Decoupling Configuration: Separates configuration from application code.
• Multiple Consumption Methods: Can be consumed as environment variables, command-line arguments, or mounted as files.

You can create a ConfigMap using the kubectl create configmap command:

Alternatively, you can define a ConfigMap in a YAML file:

Apply the YAML file using kubectl:

You can consume ConfigMap data as environment variables in a Pod:

You can also use ConfigMap data as command-line arguments:

ConfigMap data can be mounted as files in a Pod:

1. Create a ConfigMap:

   • Create a ConfigMap named app-config with the following key-value pairs:
     • database_url: jdbc:mysql://localhost:3306/mydb
     • database_user: admin
     • database_password: password

2. Consume the ConfigMap:

   • Create a Pod that uses the app-config ConfigMap. The Pod should:
     • Set environment variables DATABASE_URL, DATABASE_USER, and DATABASE_PASSWORD using the ConfigMap.
     • Print the environment variables to the console.

1. Create the ConfigMap:

   kubectl create configmap app-config --from-literal=database_url=jdbc:mysql://localhost:3306/mydb --from-literal=database_user=admin --from-literal=database_password=password
   

2. Create the Pod:

   apiVersion: v1
   kind: Pod
   metadata:
     name: app-pod
   spec:
     containers:
     - name: app-container
       image: busybox
       command: ['sh', '-c', 'echo DATABASE_URL=$DATABASE_URL; echo DATABASE_USER=$DATABASE_USER; echo DATABASE_PASSWORD=$DATABASE_PASSWORD; sleep 3600']
       env:
       - name: DATABASE_URL
         valueFrom:
           configMapKeyRef:
             name: app-config
             key: database_url
       - name: DATABASE_USER
         valueFrom:
           configMapKeyRef:
             name: app-config
             key: database_user
       - name: DATABASE_PASSWORD
         valueFrom:
           configMapKeyRef:
             name: app-config
             key: database_password
   

   Apply the Pod configuration:

   kubectl apply -f app-pod.yaml
   

• Key Not Found: Ensure the key specified in configMapKeyRef exists in the ConfigMap.
• Permissions: Make sure the Pod has the necessary permissions to access the ConfigMap.
• Environment Variable Length: Be aware of the environment variable length limits in your container runtime.

ConfigMaps are a powerful feature in Kubernetes that help you manage configuration data separately from your application code. By understanding how to create and consume ConfigMaps, you can make your applications more flexible and easier to manage. In the next topic, we will explore Secrets, which are similar to ConfigMaps but designed for sensitive data.