Using configMaps from file without mount option

General Discussions
1

Hi All,

Is it possible to use ConfigMap created using --from-file without mount option in a pod?
I have created this configmap-

$ cat amitcm.properties

msg="hello world"

msg1="welcome to this world"

$
$ k create cm amitcm --from-file amitcm.properties 
configmap/amitcm created
$ 
$ k describe cm amitcm
Name:         amitcm
Namespace:    default
Labels:       <none>
Annotations:  <none>

Data
====
amitcm.properties:
----
msg="hello world"
msg1="welcome to this world"

Events:  <none>
$

now i would like to use the key/value pair as environment variable in my pod, can this be done without using mount option ?
I would like to run this pod which writes the values of environment variables in a log file-
$cat pod.yml

apiVersion: v1
kind: Pod
metadata:
  labels:
  name: amitpod
spec:
  containers:
  - image: inboxamitraj/amitubuntu
    name: amitpod-c
    envFrom:
    - configMapRef:
        name: amitcm
    command: ["/bin/sh"]
    args: ["-c", "while true; do echo $msg $msg1>>log.txt; sleep 1;done"]

Cluster information:

Kubernetes version: v1.21.0
Cloud being used:bare-metal
Installation method: kubeadm
Host OS: ubuntu
CNI and version: weave-net 2.8.1
CRI and version: docker 18

Thank you

2

Yes.

3

Thank you @protosam
when we create configmaps from files, the filename becomes the key, now I find it very difficult
to use it as in environement variable.
eg. if my filename is cm.properties, the environement variable in my pod would be - cm.properties
but the problem is - bash does not understand a “.” dot in environement variable.

I am curious, why it is designed this way?

4

I think it’s because the environment variables are behooven to Bash/Shell programming languages.

1 Like
5

Thank you !

6

Hi @protosam,
I managed to figure it out using --from-env-file. if we create configmap this way, the key/value pair inside file are exactly created as Environment variables in the pod.

kubectl create configmap game-config-env-file \
       --from-env-file=configure-pod-container/configmap/game-env-file.properties

here is my setup

$ cat cm.properties 
msg=hello
msg1=world
$ 

$k create cm amitcm --from-env-file=cm.properties

$ cat pod.yml 
apiVersion: v1
kind: Pod
metadata:
  labels:
  name: amitpod
spec:
  containers:
  - image: inboxamitraj/amitubuntu
    name: amitpod-c
    envFrom:
    - configMapRef:
        name: amitcm
    command: ["/bin/sh"]
    args: ["-c", "while true; do echo $msg $msg1>>log.txt; sleep 1;done"]
$ 
$ k apply -f pod.yml 

$ k exec -it amitpod -- tail -f log.txt
hello world
hello world
hello world
hello world
hello world
hello world

Thank you so much for your guidance

7

Did you see that you can mount configmap data as files as well?

8

yes, exactly.
what I found is --from-file option is better if you are passing the values in file directly to your application.
–from-env-file is better if you would like your pods to use environment variables in its shell.

Thank you