Populate ConfigMap by importing data from file in k8s - kubernetes

Question

I have a requirement where i push bunch of key value pairs to a text/json file. Post that, i want to import the key value data into a configMap and consume this configMap within a POD using kubernetes-client API's.
Any pointers on how to get this done would be great.
TIA

Answer 1

You can do it in two ways.
Create ConfigMap from file as is.
In this case you will get ConfigMap with filename as a key and filedata as a value.
For example, you have file your-file.json with content {key1: value1, key2: value2, keyN: valueN}.
And your-file.txt with content
key1: value1
key2: value2
keyN: valueN
kubectl create configmap name-of-your-configmap --from-file=your-file.json
kubectl create configmap name-of-your-configmap-2 --from-file=your-file.txt
As result:
apiVersion: v1
kind: ConfigMap
metadata:
name: name-of-your-configmap
data:
your-file.json: |
{key1: value1, key2: value2, keyN: valueN}
apiVersion: v1
kind: ConfigMap
metadata:
name: name-of-your-configmap-2
data:
your-file.txt: |
key1: value1
key2: value2
keyN: valueN
After this you can mount any of ConfigMaps to a Pod, for example let's mount your-file.json:
apiVersion: v1
kind: Pod
metadata:
name: dapi-test-pod
spec:
containers:
- name: test-container
image: k8s.gcr.io/busybox
command: [ "/bin/sh","-c","cat /etc/config/keys" ]
volumeMounts:
- name: config-volume
mountPath: /etc/config
volumes:
- name: config-volume
configMap:
name: name-of-your-configmap
items:
- key: your-file.json
path: keys
restartPolicy: Never
Now you can get any information from your /etc/config/your-file.json inside the Pod. Remember that data is read-only.
Create ConfigMap from file with environment variables.
You can use special syntax to define pairs of key: value in file.
These syntax rules apply:
Each line in a file has to be in VAR=VAL format.
Lines beginning with # (i.e. comments) are ignored.
Blank lines are ignored.
There is no special handling of quotation marks (i.e. they will be part of the ConfigMap value)).
You have file your-env-file.txt with content
key1=value1
key2=value2
keyN=valueN
kubectl create configmap name-of-your-configmap-3 --from-env-file=you-env-file.txt
As result:
apiVersion: v1
kind: ConfigMap
metadata:
name: name-of-your-configmap-3
data:
key1: value1
key2: value2
keyN: valueN
Now you can use ConfigMap data as Pod environment variables:
apiVersion: v1
kind: Pod
metadata:
name: dapi-test-pod-2
spec:
containers:
- name: test-container
image: k8s.gcr.io/busybox
command: [ "/bin/sh", "-c", "env" ]
env:
- name: SPECIAL_LEVEL_KEY
valueFrom:
configMapKeyRef:
name: name-of-your-configmap-3
key: key1
- name: LOG_LEVEL
valueFrom:
configMapKeyRef:
name: name-of-your-configmap-3
key: key2
- name: SOME_VAR
valueFrom:
configMapKeyRef:
name: name-of-your-configmap-3
key: keyN
restartPolicy: Never
Now you can use these variables inside the Pod.
For more information check for documentation

Answer 2

I can also recommend Kustomize for this task. You can use it as part of your deployment pipeline to generate the K8s configuration (not only ConfigMaps, but also Deployments, NetworkPolicies, Services etc.).
In kustomize you'd need a ConfigMapGenerator. There are different options. In your case env is suitable.
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
configMapGenerator:
# generate a ConfigMap named my-system-env-<some-hash> where each key/value pair in the
# env.txt appears as a data entry (separated by \n).
- name: my-system-env
env: env.txt
Other options like files will load the whole content of the file into a single value of the ConfigMap.

Answer 3

export the key value pairs in env or text file as is identical in the container environment variables of pod using
create a config map from configmap using
kubectl create configmap special-config --from-env-file=<key value pairs file>
update the spec for the container of pod that needs these key value pairs to
envFrom:
- configMapRef:
name: special-config
Example:
apiVersion: v1
kind: Pod
metadata:
name: dapi-test-pod
spec:
containers:
- name: test-container
image: k8s.gcr.io/busybox
command: [ "/bin/sh", "-c", "env" ]
envFrom:
- configMapRef:
name: special-config
restartPolicy: Never