feat: Add --driver kubernetes

[technosophos]

This runs the invocation image inside of a Kubernetes cluster.

Use --driver kubernetes or --driver k8s to use this driver.

The driver respects the following env vars:

$KUBE_CONFIG
$KUBE_CONTEXT
$KUBE_NAMESPACE
$VERBOSE

It works by creating a secret and a pod.

• The Pod contains the invocation image
• The secret contains all files and env vars
• The secret's properties are attached to the Pod at startup
• the secret is destroyed when the pod is done

[technosophos]

• Print logs back to Duffle

[radu-matei]

This one took some thinking on a Saturday evening...

[radu-matei]

Ooh, this makes it so much cleaner than having an informer + controller (which is the solution I used when I tried this, a few Kubernetes versions ago).

[radu-matei]

The logic for waiting here is a bit confusing - as the comment when calling this function is // Waid for the pod to run to completion., but this waits for the pod to either be in Running or Succeeded state, it means the function returns when the pod first enters Running state.

I think I understand that we need to know when the pod is in Running state so we can stream the logs, but the wording here is a bit confusing.

[radu-matei]

This looks really great!

Some inspiration for attaching to the pod and streaming logs (if anyone gets to working on this before the beginning of next week) - it's for an older Kubernetes version, so there might be a shiny new way to do this.

[radu-matei]

Tried to use a bundle that requires credentials, in this case a file path:

$ duffle install hellohelm-test -f ../bundles/hellohelm/bundle.json --insecure -c hellohelm-creds --driver k8s
Executing install action...
Error: Install step failed: Secret "hellohelm-test-01cxn93m90vwgg3aga06020kwt" is invalid: data[/root/.kube/config]: Invalid value: "/root/.kube/config": a valid config key must consist of alphanumeric characters, '-', '_' or
'.' (e.g. 'key.name',  or 'KEY_NAME',  or 'key-name', regex used for validation is '[-._a-zA-Z0-9]+')

$ duffle creds show hellohelm-creds
name: hellohelm-creds
credentials:
- name: kubeconfig
  source:
    path: /home/radu/.kube/config