Problem with app dir using release

Hello,

it’s not clear what is the app dir with releases

I have files generated by the phoenix web app that can be downloaded.
They are stored in a directory called downs of the app dir. if I change release I expect these files to stay where they are and be found by all releases

I have added
plug Plug.Static, at: "/downs", from: Path.expand('./downs'), gzip: false
I then generate urls with /downs/xxx

1- if I run the app with mix phx.server from the app dir it works ok
2- if I run the app with _build/rel/prod/v1/bin/v1 start from the app dir (after having build the release) it works ok

the problem is :

3- if I upload the release previoulsy built (on another machine) to another directory test1 with the downs dir copied into test1 (but not in priv/static) , and from test1 I run v1/bin/v1 start, the app works ok but the files in downs are not found

I uploaded in test1 only the content of v1, not the full tree _build/prod/rel/v1

the url is correctly generated but looks like the plug static line is ignored in case 3

thanks for any advice

in short

> test1
> - downs
>    - file1
> - v2
>   - all files generated by mix release found under _build/prod/rel/v2 originally

file1 present when generating the release is found
but a file2 put by the application when running the release is not found for download although the url are exaclty similar

/downs/file1
/downs/file2

since file2 was put by the running application the app dir is ok but the download of the file intercepted by plug static works for file1 but not for file2