Let's say you have a deployment configured to mount a file on the host system in the container, perhaps something like this using hostPath and volumeMounts.

~]$ oc get deployment my-deployment --output yaml
spec:
  template:
    spec:
      containers:
        volumeMounts:
        - mountPath: /data/files/example.txt
          name: myfile
      volumes:
      - name: myfile
        hostPath:
          path: /home/john.doe/example.txt
          type: File

And when you attempt to create the pod, something like this is being returned.

MountVolume.SetUp failed for volume "my-file" : hostPath type check failed: /home/john.doe/example.txt is not a file

This occurs because the hostPath file needs to exist on the node the pod is running on.

Probably the most typical solution is to create a config map that contains the content of the file you want to mount in the container.

~]# oc create configmap my-config-map --from-file example.txt
configmap/my-config-map created

And then configure the deployment to use the config map.

AVOID TROUBLE

If subPath is not used, example.txt will be mounted as a directory. subPath must be used to mount example.txt as a file.

apiVersion: v1
kind: Deployment
spec:
  replicas: 1
  template:
    spec:
      containers:
      - name: my-app
        image: openshift/my-app:latest
        ports:
        - containerPort: 80
        volumeMounts:
          name: my-config-map
          mountPath: /data/files/example.txt
          subPath: example.txt
      volumes:
      - name: my-config-map
        configMap:
          name: my-config-map