instruction: Create a Dockerfile for fundamentals
output: ```dockerfile
  from the image (lowerdir) to the
  container (upperdir). The container then writes the changes to the new copy
  of the file in the container layer.However, OverlayFS works at the file level rather than the block level. This
  means that all OverlayFS copy_up operations copy the entire file, even if
  the file is large and only a small part of it's being modified. This can have
  a noticeable impact on container write performance. However, two things are
  worth noting:The copy_up operation only occurs the first time a given file is written
  to. Subsequent writes to the same file operate against the copy of the file
  already copied up to the container.OverlayFS works with multiple layers. This means that performance can be
  impacted when searching for files in images with many layers.Deleting files and directoriesWhen a file is deleted within a container, a whiteout file is created in
  the container (upperdir). The version of the file in the image layer
  (lowerdir) is not deleted (because the lowerdir is read-only). However,
  the whiteout file prevents it
  ```