Configmap

When dealing with microservices, you need to figure out how the configurations will be applied. In situations where you want to deploy to multiple environments like stage, dev and prod, it is not ideal to bake the configs into the application because of the difference in environments. Ideally you want separate configurations to match the environment you are deploying to. This is where ConfigMaps comes into play. It allows you to decouple configuration artifacts from image content. This allows containerized application to become portable without worrying about configurations. ConfigMap is similar to Secrets, but provides a way of working with strings that don’t contain sensitive information. Users and system components can store configuration data in ConfigMap.

Creating configmaps

Creating ConfigMaps is pretty simple and straightforward. You can create it with directories, file or literal values. Let us see each in action. The rest of the blog post will use a simple example to demonstrate how to work with a configmap.

From a directory

To create configmap from a directory, we must create or have an existing directory with our configs in there.

mkdir configmap-demo

wget the configs into our configmap-demo directory.

wget https://k8s.io/docs/tasks/configure-pod-container/configmap/kubectl/game.properties -O configmap-demo

wget https://k8s.io/docs/tasks/configure-pod-container/configmap/kubectl/ui.properties -O configmap-demo

What we just did was download test config files into our directory. We can then create a configmap from our directory that will have all the files we downloaded.

kubectl create configmap demo-configmap --from-file=configmap-demo

If we describe our configmap, we will see both files as data entries with their contents.

kubectl describe configmap demo-configmap

From a file

Creating from a file is very similar to creating from directory. All we need to do is pass in the name of the file to –from-file argument. When creating configmap this way, you can pass in as many files as you want to the –from-file argument and it will add it to the configmap.

From literal value

Creating configmap this way mean you can specify your configuration directly from command line without creating any file or directory. For example “kubectl create configmap special-config –from-literal=special.how=very –from-literal=special.type=charm”. You can have multiple key-value pairs if needed.

Using configmap in a pod

Lets create a test configmap

kubectl create configmap special-config --from-literal=special.how=very

Then create a pod to use the configmap as an env variable.

demo-pod.yaml

apiVersion: v1

kind: Pod

metadata:

  name: configmap-demo-pod

spec:

  containers:

    - name: test-container

      image: k8s.gcr.io/busybox

      command: [ "/bin/sh", "-c", "env" ]

      env:

        # Define the environment variable

        - name: SPECIAL_LEVEL_KEY

          valueFrom:

            configMapKeyRef:

              # The ConfigMap containing the value you want to assign to SPECIAL_LEVEL_KEY

              name: special-config

              # Specify the key associated with the value

              key: special.how

  restartPolicy: Never

kubectl create -f demo-pod.yaml

We can now see that there is an environment variable set in the pod with our defined configmap value.

kubectl logs configmap-demo-pod | grep SPECIAL_LEVEL_KEY

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