Sync two document libraries one way

[AshokYarra]

I have two Document libraries, A library in SharePoint A site, B library in SharePoint B site. I wanted to sync B library form SharePoint B to A library in SharePoint A automatically when any files is added or modified and folders.  I know, it can achieved by flow but I am looking alternative way.. How can I achieve this ?

[#2]

@AshokYarra Hello,

What is the purpose of the sync? Why does it need to be synced? 
I am asking this to see if I can provide a different solution that will meet your requirements. :)

Yours sincerely,
Aref Halmstrand

[#3]

@ArefHalmstrand Thanks for you response. As I mentioned in my previous post, SharePoint site B is customer facing site, We want to maintain all the data into a separate SharePoint repository in a sync mode that should access only internal users.