Feature: Support specifying container configuration files in Pod spec

[eliaslevy]

Currently you can parametrize a container via environment variables passed in the Pod spec. Some applications expect their configuration in the form of config files. The gap can be bridged by a helper script in the container that reads the config from an environment variable and writes it to a file before executing the app, but this is somewhat hackish for large configs. While Linux support very large environment variables, it would be more natural to pass the config to the container via a file, as the app expects.

I propose a new mechanism that would allow you to specify a config file within the spec and have the file mounted at the specified location within the container. This would work similar to a hostPath volume, but it would not require that the file pre-exist in the node the Pod executes in, and would delete the file once the Pod no longer runs.

Maybe something like:

apiVersion: v1
kind: Pod
metadata:
  name: test
spec:
  containers:
  - image: gcr.io/google_containers/test-webserver
    name: test-container
    volumeMounts:
    - mountPath: /etc/some.config
      name: config-file
  volumes:
  - name: config-file
    inlineFile:
      content: |
        foo = bar
        x = y

[mikedanese]

I feel like this is a duplicate of another issue. cc @thockin because I remember he commented on that issue and might have luck finding it.

[thockin]

This is a dup of #13610 and overlaps a lot with ConfigData. I'm wary of having too many ways to do the same thing.

@pmorie who is shepherding ConfigData.