We have seen how Docker containers are immutable; however, there are some instances when you may wish to write some files to a disk or when you want to read data from a disk such as in a development setup. Docker has the concept of volumes, which can be mounted either from the host running the Docker machine or from another Docker container.
To keep our images efficient and compact Docker uses the concept of a Union File System. The Union filesystem allows us to represent a logical file system by grouping different directories and or files together. It uses a Copy on Write technique, which copies the layer when we modify the file system, this way we only use about 1MB of space when creating a new image. When data is written to the file system Docker copies the layer and puts it on the top of the stack. When building images and extending existing images we are leveraging this technique, also when starting an image and creating a container the only difference...