rsync: how can I configure it to create target directory on server?

If you have more than the last leaf directory to be created, you can either run a separate ssh ... mkdir -p first, or use the --rsync-path trick as explained here :

rsync -a --rsync-path="mkdir -p /tmp/x/y/z/ && rsync" $source user@remote:/tmp/x/y/z/

Or use the --relative option as suggested by Tony. In that case, you only specify the root of the destination, which must exist, and not the directory structure of the source, which will be created:

rsync -a --relative /new/x/y/z/ user@remote:/pre_existing/dir/

This way, you will end up with /pre_existing/dir/new/x/y/z/

And if you want to have "y/z/" created, but not inside "new/x/", you can add ./ where you want --relativeto begin:

rsync -a --relative /new/x/./y/z/ user@remote:/pre_existing/dir/

would create /pre_existing/dir/y/z/.

Assuming you are using ssh to connect rsync, what about to send a ssh command before:

ssh user@server mkdir -p existingdir/newdir

if it already exists, nothing happens

The -R, --relative option will do this.

For example: if you want to backup /var/named/chroot and create the same directory structure on the remote server then -R will do just that.