How to align a node's text RIGHT, i.e. at the end of the line?

I’m drawing a diagram with nodes and I have to have the inner text of one node at the END of the line, i.e. at the right side, not left, not centered. Unfortunately I didn’t find a way nor information in the web.

That’s how my picture now looks like:

As you can see the text in the node “Client” (right side) is covered by the “Anwendungsprogramm”-node. How can I shove the text on the right side of the node?

The code:
(It’s a large document, that’s why I use this many packages. For I’m not sure which packages do influence my graphics, I’ll take all.)

usepackage[babel, german=quotes]{csquotes}
usepackage{array}
usepackage[style=alphabetic, backend=bibtex8]{biblatex}
usepackage{setspace}
usepackage{geometry}
usepackage[table]{xcolor} 
usepackage[arrow, matrix, curve]{xy}
usepackage{calc}
usepackage{multirow}
usepackage{tikz}
usetikzlibrary{matrix,calc,positioning,arrows}

begin{document}

begin{figure}[htbp]
begin{center}      
begin{tikzpicture}     

    node [rectangle, rounded corners=1mm, minimum size=25mm, text width=40mm,
            anchor=base, very thick, draw=black!50, fill=black!10]                      
           (server)     {Server};

    node [rectangle, rounded corners=1mm, minimum size=20mm, text width=25mm, 
            anchor=base, very thick, draw=black!50, text centered, 
           right=20mm of server]    
           (webservice) {Webservice};              

    node [rectangle, rounded corners=1mm, minimum size=20mm, text width=20mm, 
            anchor=base, very thick, draw=black!50, fill=white!100, text centered, 
           right=-25mm of server]   
           (server-p)   {Anwen- dungs- programm};              

    node [rectangle, rounded corners=1mm, minimum size=25mm, text width=40mm, 
            anchor=base, very thick, draw=black!50, fill=black!10, text centered, 
           right=20mm of webservice]    
           (client) {Client};          

    node [rectangle, rounded corners=1mm, minimum size=20mm, text width=20mm, 
            anchor=base, very thick, draw=black!50, fill=white!100, text centered, 
           left=-25mm of client]    
           (client-p)   {Anwen- dungs- programm};

    draw [<->, very thick] (webservice) to (server-p);
    draw [<->, very thick] (webservice) to (client-p);

end{tikzpicture}
bigskip
label{fig-funktionaleebenen}   
end{center}    
end{figure}

end{document}

documentclass[12pt, a4paper]{scrartcl}
usepackage[babel, german=quotes]{csquotes}
usepackage[style=alphabetic, backend=bibtex8]{biblatex}
usepackage[table]{xcolor} 
usepackage[arrow, matrix, curve]{xy}
usepackage{calc,multirow,tikz,array,setspace,geometry}
usetikzlibrary{matrix,calc,positioning,arrows}

begin{document}
begin{tikzpicture}     

    node [rectangle, rounded corners=1mm, minimum size=25mm, text width=40mm,
            anchor=base, very thick, draw=black!50, fill=black!10]                      
           (server)     {Server};

    node [rectangle, rounded corners=1mm, minimum size=20mm, text width=25mm, 
            anchor=base, very thick, draw=black!50, text centered, 
           right=20mm of server]    
           (webservice) {Webservice};              

    node [rectangle, rounded corners=1mm, minimum size=20mm, text width=20mm, 
            anchor=base, very thick, draw=black!50, fill=white!100, text centered, 
           right=-25mm of server]   
           (server-p)   {Anwen- dungs- programm};              

    node [rectangle, rounded corners=1mm, minimum size=25mm, text width=40mm, 
            anchor=base, very thick, draw=black!50, fill=black!10, align = right, 
           right=20mm of webservice]    
           (client) {Client};          

    node [rectangle, rounded corners=1mm, minimum size=20mm, text width=20mm, 
            anchor=base, very thick, draw=black!50, fill=white!100, text centered, 
           left=-25mm of client]    
           (client-p)   {Anwen- dungs- programm};

    draw [<->, very thick] (webservice) to (server-p);
    draw [<->, very thick] (webservice) to (client-p);

end{tikzpicture}
end{document}