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16-k8s-lab-configmap.md

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ConfigMap

References:
ConfigMaps
Kubernetes API: ConfigMap

Agenda

  • Overview.
  • Create a ConfigMap and a Pod that uses this ConfigMap.
  • Cleanup.

Start a Kubernetes cluster using minikube start.

Background
A ConfigMap is an API object used to store non-confidential data in key-value pairs. A ConfigMap allows you to decouple environment-specific configuration from your container images, so that your applications are easily portable.
Pods can consume ConfigMaps as environment variables, command-line arguments, or as configuration files in a volume. This decision should be based on how your application reads its config values.

  • ConfigMaps consumed as environment variables are not updated automatically and require a pod restart.
  • ConfigMaps consumed as mounted volumes are updated automatically and don't require a pod restart.
    Note: A container using a ConfigMap as a subPath volume mount will not receive ConfigMap updates.

Create ConfigMap and Pod using config file

Create the manifest. Save the following YAML file in your directory.
File: 10-k8s-configmap-env-vol.yaml

ConfigMap and Pod manifest

Apply the configuration using kubectl apply -f YAML_FILE.

~/learnk8s> kubectl apply -f yaml/10-k8s-configmap-env-vol.yaml 
configmap/mycfgmap created
pod/mypod created

Verification

Get a shell to the Pod.

~/learnk8s> kubectl exec -i -t mypod -- /bin/bash

Run the commands as shown below.

root@mypod:/# pwd
/
root@mypod:/# ls
bin  boot  config  dev  docker-entrypoint.d  docker-entrypoint.sh  etc  home  lib  lib64  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var
root@mypod:/# echo $ENV
dev
root@mypod:/# cd config/
root@mypod:/config# ls
debug.properties  dest.properties
root@mypod:/config# cat dest.properties 
Q_INPUT=InputQ
Q_OUTPUT=OutputQ
root@mypod:/config# cat debug.properties 
TracerMode=always
LogLevel=INFO
root@mypod:/config# exit
exit
~/learnk8s>

Cleanup
Delete the configuration using kubectl delete -f YAML_FILE.

~/learnk8s> kubectl delete -f yaml/10-k8s-configmap-env-vol.yaml 
configmap "mycfgmap" deleted
pod "mypod" deleted