Revisit idea of a shared volume in the same pod for NGINX and PHP-FPM for Drupal static files

[krook]

• https://kubernetes.io/docs/tasks/access-application-cluster/communicate-containers-same-pod-shared-volume/
• https://kubernetes.io/docs/concepts/workloads/pods/pod/

This would avoid duplication of Drupal content between web server and PHP node, but it would also imply that the containers are forced to all be on the same host, and that they can't scale independently.

[krook]

Using a shared volume mount presents performance problems. Including:

• The initialization of the volume can take a long time over NFS.
• Each successive startup that also checks the volume and needs to copy over changed files takes a long time with rsync

Richard has explored a sidecar approach that is promising, but the downside is that it still copies code, rather than putting in a place that's shared for modification by drush