Looking for a safe way to deploy PHP code

Question

How we do things now

We have a file server (using NFS) that multiple web servers mount and use these mounts as the web root. When we deploy our codebase, we SCP an archive (tar.gz) to the NFS server and unarchive the data directly in the "web directory" of file server.

The issue

During the deploy process we are seeing some i/o errors, mostly when a requested file cannot be read: Smarty error: unable to read resource: "header.tpl" These errors seem to go away after the deploy is finished, so we assume that it's because unarchiving the data directly to the web directory isn't the safest of things. I'm guessing we need something atomic.

My Question

How can we atomically copy new files into an existing directory (the web server's root directory)?

EDIT

The files that we are uncompromising into the web directory are not the only files that are in the directory. We are adding files to the directory, that already has files. So copying the directory or using a symlink is not an option (that I know of).

Answer 1

Here's what I do.

DocumentRoot is, for example, /var/www/sites/www.example.com/public_html/:

cd /var/www/sites/www.example.com/
svn export http://svn/path/to/tags/1.2.3 1.2.3
ln -snf 1.2.3 public_html

You could easily modify this to expand your .tar.gz before changing the symlink instead of exporting from svn. The important part is that the change is the atomic application of the symlink.