kubernetes: using value of runAsUser in an environment variable using valueFrom?

Question

I have a kubernetes deployment that starts a pod that includes a runAsUser key in its securityContext. I was hoping I could stick this value in the environment of an initContainer using valueFrom, like this:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: testdeployment
spec:
  template:
    spec:
      containers:
        - name: myservice
          image: myimage
          securityContext:
            runAsUser: 1000
      initContainers:
        - name: initialize_things
          image: myimage
          env:
            - name: CONTAINER_UID
              valueFrom:
                fieldRef:
                  fieldPath: spec.containers[0].securityContext.runAsUser

That doesn't seem to work:

The Deployment "testdeployment" is invalid: spec.template.spec.initContainers[0].env[0].valueFrom.fieldRef.fieldPath: Invalid value: "spec.containers[0].securityContext.runAsUser": error converting fieldPath: field label not supported: spec.containers[0].securityContext.runAsUser

Is there any way to make this work? I'm trying to reduce the number of places I'm hardcoding that UID.

Answer 1

I think you cant make this work because The downward API doesnt support spec.containers[0].securityContext.runAsUser as a field.

Btw, in your case more logically was to put full path , I mean spec.template.spec.containers[0].securityContext.runAsUser, but anyway, it wont help

As per Capabilities of the Downward API - you are able to use only few fields

Information available via fieldRef:
metadata.name 
metadata.namespace
metadata.uid 
metadata.labels['<KEY>']
metadata.annotations['<KEY>'] 

In addition, the following information is available through downwardAPI volume fieldRef:    
metadata.labels
metadata.annotations 

The following information is available through environment variables:    
status.podIP 
spec.serviceAccountName 
spec.nodeName 
status.hostIP

You can find very similar issue on github closed: how to get imageID in container