Kubernetes - ConfigMap

tags: Kubernetes

Foreword

When you are developing, you don't want to deliver your code of the deployment environment with your code together. The ConfigMap is the useful object to help you.

Once you deliver your code of the deployment environment with your code together, it will let your service expose in danger.

ConfigMap

Definition

A ConfigMap is an API object used to store non-confidential data in key-value pairs. Pods can consume ConfigMaps as environment variables, command-line arguments, or as configuration files in a volume.

Secret V.S. ConfigMap

Somebody will have question between Secret and ConfigMap. Usually, we save the data need to be encrypted in Secret such like password of database or password of API. However, in the ConfigMap we usually save the port number or config file of Redis.

Feature of ConfigMap

• We don't need to modify the container, we can change the different enviroment.
• A ConfigMap can save whole configuration, ex webserver config file, Nginx config file.
• ConfigMap can save all of our configuration.

Practice

Create ConfigMap

From literal

We can use the literal to create the ConfigMap.

$ kubectl create configmap myconfig --from-literal=k1=v1 --from-literal=k2=v2
configmap "myconfig" created

Use kubectl get to check our ConfigMap.

kubectl get configmap myconfig -o yaml

From yaml file

We can use yaml file to create ConfigMap.

apiVersion: v1
kind: ConfigMap
metadata:
  name: myconfigyaml
data:
  k1: v1 
  k2: v2

Then create ConfigMap.

kubectl apply -f ./myconfig.yaml

Or you use file to create ConfigMap. First, create a file and write the value.

fromkey1=v1
fromkey2=v2
fromkey3=v3

And, use kubectl create configmap myconfigfromkey --from-key=[key]=[file path] to create ConfigMap.

$ kubectl create configmap myconfigfromkey --from-file=fromfilekey=from-key

Use ConfigMap

Create a Pod let ConfigMap as environment varible.

apiVersion: v1
kind: Pod
metadata:
  name: config-pod
spec:
  containers:
  - name: config-pod
    image: gcr.io/google_containers/busybox
    command: ["/bin/sh", "-c", "env"]
    env:
    - name: MY_CONFIG_KEY
      valueFrom:
        configMapKeyRef:
          name: myconfig
          key: k1
  restartPolicy: Never

We can see the log of Pod. We will see like this.

$ kubectl logs config-pod
...
MY_CONFIG_KEY=v1

We can see MY_CONFIG_KEY=v1. It is which we define in the yaml file.

Reference

https://kubernetes.io/docs/concepts/configuration/configmap/

https://ithelp.ithome.com.tw/articles/10193935

https://ithelp.ithome.com.tw/articles/10196153