How to merge two folders?

Question

linux

There is a folder A in which files are stored, various services read from it. A new folder B appeared on the server. Is it possible to somehow merge them so that the final folder name also remains A, but when new files were created in it, they were written to folder B. And therefore, when requesting new files from A, they were pulled from B without any problems (since, according to the first condition, new files should be created there through A).
How can this be done, if possible? What instruments to watch?

Answer 1

Symlink? https://wiki.debian.org/SymLink
https://ru.wikipedia.org/wiki/%D0%A1%D0%B8%D0%BC%D...

Answer 2

merge two directories via cascading google mount
Unionfs, Aufs, Overlayfs.
examples of application in tyrnet in bulk.
there are differences in features, functionality, stability...

Answer 3

1. a specific task what exactly you are trying to do
what language the software engine is doing. maybe there is a solution not through what you suggested, for example
, it looks like one ifka in a soft
, so say what exactly you are doing and why exactly