Introduction to ConfigMaps

ConfigMaps in Kubernetes allow you to separate configuration data from the application code. This helps in maintaining cleaner, more modular code and provides an easier way to manage configurations.

Creating and Managing ConfigMaps

To create a ConfigMap, you can use either a YAML file or direct kubectl commands.

Using YAML

Create a file named my-configmap.yaml with the following content:

apiVersion: v1
kind: ConfigMap
metadata:
  name: my-configmap
data:
  key1: value1
  key2: value2

Run this command to apply it:

kubectl apply -f my-configmap.yaml  

Using kubectl Directly

To create a ConfigMap directly from the command line:

kubectl create configmap my-configmap --from-literal=key1=value1 --from-literal=key2=value2

List ConfigMaps

kubectl get configmaps  

Using ConfigMaps in Pods and Applications

You can use ConfigMaps in various ways such as environment variables, command line arguments, or as a file in a volume.

Environment Variable

Create a Pod definition file (pod-using-configmap.yaml):

apiVersion: v1
kind: Pod
metadata:
  name: mypod
spec:
  containers:
  - name: my-container
    image: busybox
    envFrom:
    - configMapRef:
        name: my-configmap

Apply it:

kubectl apply -f pod-using-configmap.yaml  

As Volume

In your Pod definition, you can specify the ConfigMap as a volume:

  volumes:
  - name: config-volume
    configMap:
      name: my-configmap

Best Practices and Limitations

1. Immutable ConfigMaps: Consider making ConfigMaps immutable if they shouldn’t be changed during the lifecycle of the Pod.
2. Size Limit: ConfigMaps have a size limit of 1MiB.

ConfigMaps vs Secrets

1. Sensitivity: ConfigMaps are not designed to hold sensitive information, unlike Secrets.
2. Encryption: Secrets are encrypted at rest, ConfigMaps are not.

Complete Exercise: Using ConfigMap with a Pod

Setup

1. Create a ConfigMap:

kubectl create configmap my-configmap --from-literal=key1=value1

Steps

1. Create a Pod that uses this ConfigMap as an environment variable.

apiVersion: v1
kind: Pod
metadata:
  name: mypod
spec:
  containers:
  - name: my-container
    image: busybox
    envFrom:
    - configMapRef:
        name: my-configmap

2. Apply the Pod:

kubectl apply -f pod-using-configmap.yaml

Troubleshooting

• Run kubectl describe pod mypod to check for issues.
• Make sure the ConfigMap exists: kubectl get configmaps

Solution

The Pod should be running with environment variables loaded from the ConfigMap. Validate this by running:

kubectl exec -it mypod -- env

You should see key1=value1 among the environment variables.