Inject host's environment variable into K8s Pod

Question

I would like to run a pod on one of my IoT devices. Each one of those devices contains an environment variable I want this pod to use. Is there any way to inject this env variable into the pod using build-in templating of helm/kubectl? I was trying the following on my deployment.yaml file:

env: 
  - name: XXX
    value: $ENV_FROM_HOST

but when executing the pod and trying the get XXX value, I get the string $ENV_FROM_HOST instead of its value from the host:

$ echo $XXX
$ENV_FROM_HOST

Thanks.

Answer 1

It's not possible to directly pass the host's env vars to the pods. I often do that by creating a ConfigMap.

1. Create a ConfigMap with from-lireral option:

   kubectl create configmap testcm --from-literal=hostname=$HOSTNAME
   

2. Refer to that in the Pod's manifest:

   - name: TEST
     valueFrom:
       configMapKeyRef:
         name: testcm
         key: hostname
   

This will inject the host's $HOSTNAME into the Pod's $TEST.

If it's sensitive information, you can use Secrets instead of using ConfigMap.