ConfigMaps

ConfigMaps Part 2

ConfigMaps are used to store non-sensitive application configuration parameters. Think of config files managed by Kubernetes and you are already close.

Creating a ConfigMap

There are multiple ways of creating a ConfigMap. They can be created from files, directories or by providing values directly using the command line [3].

Although ConfigMaps are key value pairs, this does not mean that values have to be very short. In fact, a value can contain content up to 1 megabyte of non-binary UTF-8 text.

Creating a ConfigMap from a Configuration File

The example 20-config-file.conf contains an imaginary configuration file:

# This is an exemplary config file

number-of-requests = 20
very-import-switch = true

To import the config file into a ConfigMap execute the following command:

kubectl create configmap config-example-1 --from-file=20-config-file.conf

To verify that the ConfigMap has been created successfully:

kubectl get configmaps config-example-1 -o yaml

The -o yaml switch has the effect that not only the ConfigMap is listed but also its content shown. You should see a section data contain the content of the imported configuration file.

Creating a ConfigMap from Command Line Literals

It is also possible to specify ConfigMaps using command line literals:

kubectl create configmap config-example-2 --from-literal=number-of-requests=20 --from-literal=very-important-switch=true

See yourself how the key values pairs have been joined into a ConfigMap:

kubectl get configmaps config-example-2 -o yaml

Deleting a ConfigMap

Deleting a ConfigMap is simple:

kubectl delete configmap config-example-1
kubectl delete configmap config-example-2

Accessing ConfigMaps

Once a ConfigMap is created Kubernetes offers several access mechanisms to applications.

Env Variable
Filesystem

In order to grant an application access to a ConfigMap it must be told which ConfigMap to access and which mechanism is to be used. This is done in the Pod spec:

See YAML file: 40-pod-with-config-map-env.yml:

apiVersion: v1
kind: Pod
metadata:
  name: busybox-config
spec:
  containers:
    - image: busybox
      name: busybox-config-container
      command:
        - 'env'
      env:
        - name: NUMBER_OF_REQUESTS
          valueFrom:
            configMapKeyRef:
              name: config-example-2
              key: number-of-requests
        - name: VERY_IMPORTANT_SWITCH
          valueFrom:
            configMapKeyRef:
              name: config-example-2
              key: very-important-switch
  restartPolicy: Never

Apply the YAML file:

kubectl apply -f 40-pod-with-config-map-env.yml

Verify whether the Pod has been created successfully:

kubectl get pod busybox-config

You should see an error with the STATUS field indicating CreateContainerConfigError. This gives you the opportunity to think about how a failing Pod can be investigated. Maybe it's worth having a look at the Pod's log output:

kubectl logs busybox-config

But the output is disappointing:

error: the server doesn't have a resource type "logs"

Why are there no logs?

The answer is because there is no Pod that could produce logs as the Pod creation failed. At this stage the kubectl log command is not helpful.

As a general utility to investigate Kubernetes objects - not only Pod objects - the kubectl describe command is very handy:

kubectl describe Pod busybox-config

At the end of the output a tabular paragraph Events tells us about the lifecycle events of our busybox-config Pod:

Error: configmap "config-example-2" not found

Exercise

Try to fix the above ConfigMap not found issue.

If you have fixed the issue, the container named busybox-config should have been started successfully.

Then:

kubectl logs busybox-config

Should return the environment variables seen by the container inside the busybox-config Pod. The listing should include:

NUMBER_OF_REQUESTS=20
VERY_IMPORTANT_SWITCH=true

Also have a look at all the other environment variables added by Kubernetes:

PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOSTNAME=busybox-config
APP_GAMMA_SERVICE_PORT_8080_TCP_PORT=8080
KUBERNETES_SERVICE_HOST=10.100.200.1
KUBERNETES_PORT_443_TCP_PROTO=tcp
APP_GAMMA_SERVICE_SERVICE_HOST=10.100.200.246
APP_GAMMA_SERVICE_PORT_8080_TCP=tcp://10.100.200.246:8080
KUBERNETES_SERVICE_PORT_HTTPS=443
APP_GAMMA_SERVICE_PORT_8080_TCP_PROTO=tcp
APP_GAMMA_SERVICE_PORT_8080_TCP_ADDR=10.100.200.246
KUBERNETES_PORT=tcp://10.100.200.1:443
KUBERNETES_PORT_443_TCP_ADDR=10.100.200.1
APP_GAMMA_SERVICE_SERVICE_PORT=8080
APP_GAMMA_SERVICE_PORT=tcp://10.100.200.246:8080
KUBERNETES_SERVICE_PORT=443
KUBERNETES_PORT_443_TCP=tcp://10.100.200.1:443
KUBERNETES_PORT_443_TCP_PORT=443
HOME=/root

It's worth remembering that Kubernetes provides you with context information of the execution environment.

Related Videos​

ConfigMaps Part 2

Creating a ConfigMap​

Creating a ConfigMap from a Configuration File​

Creating a ConfigMap from Command Line Literals​

Deleting a ConfigMap​

Accessing ConfigMaps​

Exercise​

Links​

Related Videos