How to realize sync a website image store directory?

How can I realize the website code and images' redundancy?

I have two servers:

You can see the mysql database can use the master-slave replication to sync the database.

but there is the issue to me, I want to the website's image store directory also sync the data.

I mean, if the Server A's /www/website_name/data/images add an image the Server B's same name directory should also add an image.

How to realize this requirement?