How to make a symlinked folder appear as a normal folder

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I have two Dart applications I need to dockerize. These two apps use a shared source directory.
Because Docker prevents adding files from folders outside the context directory (project/app1) I can’t add files from ../shared nor from shared (the symlink inside projects/app1).

I’m looking for a way to trick Docker to do it anyway.

My simplified project structure 

- projects
  - app1
   - Dockerfile
   - shared (symlink ../shared)
   - otherSource
  - app2
   - Dockerfile
   - shared (symlink ../shared)
   - otherSource
  - shared
    - source

I could move Dockerfile one level up and run docker build from there but then I need two Dockerfiles (for app1 and app2) in the same directory.

My current idea was, if I could somehow hide the fact that projects/app1/shared is a symlink this problem would be solved.
I checked if I can share projects using Samba and remount it somewhere else and configure Samba to treat symlinks like normal folders but haven’t found whether this is supported (I have not much experience with Samba and not tried it yet, just searched a bit).

Is there any other tool or trick that would allow that?

I would rather not change the directory structure because this would cause other troubles and also rather not copy files around.

Answer

I don’t have much experience with docker so I can’t promise this will work but one choice would be to mount the directory instead of linking to it:

$ cd projects/app1
$ mkdir shared
$ sudo mount -o bind ../shared shared/

That will attach ../shared to ./shared and should be completely transparent to the system. As explained in man mount:

The bind mounts.

Since Linux 2.4.0 it is possible to remount part of the file hierarchy somewhere else. The call is:

mount --bind olddir newdir

or by using this fstab entry:

/olddir /newdir none bind

After this call the same contents are accessible in two places.

Attribution
Source : Link , Question Author : zoechi , Answer Author : terdon

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