Docker uses the copy-on-write technique when dealing with images. Copy-on-write is a strategy of sharing and copying files for maximum efficiency. If a layer uses a file or folder that is available in one of the low-lying layers, then it just uses it. If, on the other hand, a layer wants to modify, say, a file from a low-lying layer, then it first copies this file up to the target layer and then modifies it. In the following figure, we can see a glimpse of what this means:
Copy-on-write
The second layer wants to modify File 2, which is present in the base layer. Thus, it copied it up and then modified it. Now, let's say that ...
