How to align nodes in a layered block diagram in tikz?

Question

I want to document layered software architectures and protocol stacks using TikZ. Each layer has one or more elements, and there is no strict association between elements that are above each other. I tried this:

\documentclass[tikz]{standalone}
\begin{document} 
\begin{tikzpicture}
    \node (a1) [draw] { A1 };
    \node (a2) [draw,right of=a1] { A2gq };
    \node (a3) [draw,right of=a2] { A3 };
    \node (b1) [draw,below of=a1] { B1 };
    \node (b2) [draw,right of=b1] { B2 };
    \node (b3) [draw,right of=b2] { B3gq };
    \node (b4) [draw,right of=b3] { B4 };
    \node (c1) [draw,below of=b1] { C1 };
    \node (c2) [draw,right of=c1] { C2gq };
    \node (c3) [draw,right of=c2] { C3 };
\end{tikzpicture}
\end{document}

Which looks terrible - especially since the base lines of the nodes are not aligned (nodes containing g or q are higher):

I would like it to look like this:

Without having to calculate or guess lots of coordinates manually, in order to not complicate modifying the contents. I especially would like the right borders of the boxes to be aligned in order to get a cleaner look. This would be achieved by expanding nodes in rows that are shorter than the longest one, like words in a "justified" (in opposition to "ragged-left") text. The diagram will be used in a "beamer" presentation. Is there an easy way to do that?

Answer 1

Here is a proposal following the end of section 5.1 of the pgfmanual. In addition the positioning library is loaded.

\documentclass[tikz]{standalone}
\usetikzlibrary{positioning}
\begin{document} 
\begin{tikzpicture}[every node/.append style={minimum height=7mm,
text depth=0.25ex,draw},node distance=9mm and 3mm]
    \node (a1)  { A1 };
    \node (a2) [right=of a1] { A2gq };
    \node (a3) [right=of a2] { A3 };
    \draw[red] (a1.base -| a1.west) -- (a3.base -| a3.east);
    \node (b1) [below of=a1] { B1 };
    \node (b2) [right=of b1] { B2 };
    \node (b3) [right=of b2] { B3gq };
    \node (b4) [right=of b3] { B4 };
    \draw[red] (b1.base -| b1.west) -- (b4.base -| b4.east);
    \node (c1) [below of=b1] { C1 };
    \node (c2) [right=of c1] { C2gq };
    \node (c3) [right=of c2] { C3 };
\end{tikzpicture}
\end{document}

The red lines are just for illustration and should be removed of course.

UPDATE: Make sure that the outer ends of the rows are aligned. EDIT: Unified the positioning syntax, big thanks to @sgmoye!

\documentclass[tikz]{standalone}
\usetikzlibrary{positioning,fit}
\begin{document} 
\begin{tikzpicture}[every node/.append style={minimum height=7mm,
text depth=0.25ex,draw},node distance=3mm and 3mm]
    \node (b1)  { B1 };
    \node (b2) [right=of b1] { B2 };
    \node (b3) [right=of b2] { B3gq };
    \node (b4) [right=of b3] { B4 };
    \node (a1) [above=of b1] { A1 };
    \node (f1) [inner sep=-\pgflinewidth*0.5pt,fit=(b2.west|-a1.north) (b3.east|-a1.south)]{};
    \node (a3) [above=of b4] { A3 };
    \path (a1) -- (a3) node[midway,draw=none] (a2) { A2gq };
    \node (c1) [below=of b1] { C1 };
    \node (f1) [inner sep=-\pgflinewidth*0.5pt,fit=(b2.west|-c1.north) (b3.east|-c1.south)]{};
    \node (c3) [below=of b4] { C3 };
    \path (c1) -- (c3) node[midway,draw=none] (c2) { C2gq };
\end{tikzpicture}
\end{document}

ADDENDUM: A not so fiddly solution. No packages. Just for fun.

\documentclass{article}
\begin{document}
\begin{minipage}{5cm}
\fbox{ A1 }\hfill\fbox{ A2gq }\hfill\fbox{ A3 }\\[4mm]
\fbox{ B1 }\hfill\fbox{ B2 }\hfill\fbox{ B2gq }\hfill\fbox{ B4 }\\[4mm]
\fbox{ C1 }\hfill\fbox{ C2gq }\hfill\fbox{ C3 }
\end{minipage}
\end{document}

ADDENDUM: A bit more seriously: if you wish to combine the nice feature of \hfill with TikZ, then you may want to have a look at this snippet.

\documentclass{article}
\usepackage{tikz}
\newcounter{tikzbox}
\newcommand{\tikzbox}[2][]{\stepcounter{tikzbox}
\tikz[remember picture]{\node[draw,minimum height=7mm,
text depth=0.25ex,#1](tikzbox-\thetikzbox){#2};}}
\begin{document}
\begin{minipage}{5cm}
\tikzbox{A1}\hfill\tikzbox{A2gq}\hfill\tikzbox{A3}\\[4mm]
\tikzbox[alias=pferd]{B1}\hfill\tikzbox[alias=hase]{B2}\hfill\tikzbox{B2gq}\hfill\tikzbox{B4}\\[4mm]
\tikzbox{C1}\hfill\tikzbox{C2gq}\hfill\tikzbox{C3}
\end{minipage}
\tikz[overlay,remember picture]{%
\draw[thin,red] (tikzbox-1.base) -- (tikzbox-3.base);
\draw[thick,-latex] (pferd) -- (hase);
}
\end{document}

The red line is just for illustration, and there is some more serious application as well. The nodes get auto-labeled, but you can give them your own names using alias.

Answer 2

I just discovered TikZ's execute at begin node function. Very handy. It is used on pages 79 and 80 of the TikZ user guide, though I cannot find it discussed there. This essentially does what @marmot proposes but uses a \strut to accomplish it.

\documentclass[tikz]{standalone}
\usetikzlibrary{positioning}
\begin{document} 
\begin{tikzpicture}[every node/.style={draw,execute at begin node=\strut}]
    \node (a1) { A1 };
    \node (a2) [right=of a1] { A2gq };
    \node (a3) [right=of a2] { A3 };
    \node (b1) [below=of a1] { B1 };
    \node (b2) [right=of b1] { B2 };
    \node (b3) [right=of b2] { B3gq };
    \node (b4) [right=of b3] { B4 };
    \node (c1) [below=of b1] { C1 };
    \node (c2) [right=of c1] { C2gq };
    \node (c3) [right=of c2] { C3 };
\end{tikzpicture}

\end{document}

Update

As I am not a fan of excessive markup, that word 'fiddly' got my attention, as did @marmot's non-TikZ solution (smart!). So I offer this:

\documentclass{article}

\usepackage{tikz}    
%% #1 the distance over which nodes are spread;
%% #2 comma-separated list of node contents.
\newcommand{\stretchtowidth}[2]{%
    \begingroup
    \tikzset{every node/.style={draw}}%
    \hbox to #1{%
        \foreach \n in {#2}{\tikz\node{\strut\n};\hfill}\unskip}%
    \endgroup
}

\begin{document} 

\stretchtowidth{1.25in}{A1,A2gq,A3}

\medskip

\stretchtowidth{1.25in}{B1,B2,B3gq,B4}

\medskip

\stretchtowidth{1.25in}{C1,C2gq,C3}

\end{document}

Answer 3

A solution using the chains library.

\documentclass[tikz]{standalone}
\usetikzlibrary{chains}
\begin{document} 
    \begin{tikzpicture}[
        start chain=A going right,
        start chain=B going right,
        start chain=C going right,
        outer sep=0pt,
        inner sep=.2em,
        node distance=1.6em and .25em,
        every node/.style={draw, anchor=base, text height=0.8em, text depth=0.25ex}]
        \node (a1) [on chain=A] {A1};
        \node [on chain=A] {A2gq};
        \node [on chain=A] {A3};
        \node (b1) [on chain=B, below of=a1] {B1};
        \node [on chain=B] {B2};
        \node [on chain=B] {B3gq};
        \node [on chain=B] {B4};
        \node [on chain=C, below of=b1] {C1};
        \node [on chain=C] {C2gq};
        \node [on chain=C] {C3};
    \end{tikzpicture}
\end{document}

Answer 4

When these distributions are more o less regular, you can use a tcbposter (from tcolorbox). Following code tries to mimmic linked protocol stack with a tcbposter. I've supposed a 8 columns x 9 rows distribution where right most column is two column wide. As first 8 rows show a regular distribution it has been easy to place all boxes.

For the 9th row I used width tcolorbox option instead of span to define the correct width after solving following equation for \mylength

5*\mylength+4*\tcbpostercolspacing = 6*\tcbpostercolwidth + 5*\tcbpostercolspacing

After that, placement of boxes are fixed with xshift.

\documentclass[border=2mm]{standalone}

\usepackage[most]{tcolorbox}
\usepackage{lmodern}
\usepackage{lipsum}
%\usepackage{geometry}

\standaloneenv{tcbposter}

%\pagestyle{empty}
\begin{document}

\begin{tcbposter}[%
    poster = {columns=8, rows=9, width=17cm, height=8cm, spacing=1mm},% showframe},
    boxes = {colback=cyan!80!black, 
        boxrule=0pt, arc=2mm,
        colframe=cyan!80!black, 
        halign=center, valign=center,   
        colupper=white,
        fontupper=\sffamily\bfseries, size=small}
]
%1st row
\posterbox{column=1, row=1}{HTTP}
\posterbox{column=2, row=1}{HTTP/2}
\posterbox{column=3, row=1}{MQTT}
\posterbox{column=4, row=1}{CoAP}
\posterbox{column=5, row=1}{FTP}
\posterbox{column=6, row=1}{TFTP}

%2nd row
\posterbox{column=1, row=2}{SMTP}
\posterbox{column=2, row=2}{SNTP}
\posterbox{column=3, row=2}{DNS}
\posterbox{column=4, row=2}{NetBIOS}
\posterbox{column=5, row=2, span=2}{SNMPv1/v2c/v3}

%3rd row
\posterbox{column=1, row=3, span=2}{WebSocket}
\posterbox{column=3, row=3}{mDNS}
\posterbox{column=4, row=3}{DNS-SD}
\posterbox{column=5, row=3}{DHCP}
\posterbox{column=6, row=3}{DHCPv6}

%4th row
\posterbox{column=1, row=4,span=6}{Socket}

%5th row
\posterbox{column=1, row=5, span=2.5}{TCP}
\posterbox{column*=5, row=5, span=2.5}{UDP}
\posterbox{column=6, row=5}{RAW}

%6th row
\posterbox{column=1, row=6, span=3}{IPv4}
\posterbox{column=4, row=6, span=3}{IPv6}

%7th row
\posterbox{column=1, row=7, span=1.5}{ARP}
\posterbox{column*=3, row=7, span=1.5}{Auto-IP}
\posterbox{column=4, row=7, span=1.5}{NDP}
\posterbox{column*=6, row=7, span=1.5}{SLAAC}

%8th row
\posterbox{column=1, row=8, span=1.5}{ICMP}
\posterbox{column*=3, row=8, span=1.5}{IGMPv2}
\posterbox{column=4, row=8, span=1.5}{ICMPv6}
\posterbox{column*=6, row=8, span=1.5}{MLDv1}

%9th row
%5 boxes and 4 separations should use 
%equivalent to 6 original boxes plus 5 
%separations 
\newlength{\mylength}
\pgfmathsetlength{\mylength}{(6*\tcbpostercolwidth+\tcbpostercolspacing)/5}%

%Use `width` instead of `span` to fix box size
\posterbox[width=\mylength]{name=91, column=1, row=9}{Ethernet}
\posterbox[width=\mylength]{name=92, column=1, row=9, xshift=\mylength+\tcbpostercolspacing}{Wi-Fi}
\posterbox[width=\mylength]{name=92, column=1, row=9, xshift=2*\mylength+2*\tcbpostercolspacing}{PPP}
\posterbox[width=\mylength]{name=92, column=1, row=9, xshift=3*\mylength+3*\tcbpostercolspacing}{USB/RNDIS}
\posterbox[width=\mylength]{column*=6, row=9}{G3-PLC}

%Right column
\posterbox[colback=gray, colframe=gray, colupper=black]{column=7, row=1, span=2, rowspan=3}{7 - Application}
\posterbox[colback=gray!80, colframe=gray!80, colupper=black]{column=7, row=4, span=2}{5 - Session}
\posterbox[colback=gray!60, colframe=gray!60, colupper=black]{column=7, row=5, span=2}{4 - Transport}
\posterbox[colback=gray!40, colframe=gray!40, colupper=black]{column=7, row=6, span=2, rowspan=3}{3 - Network}
\posterbox[colback=gray!20, colframe=gray!20, colupper=black]{column=7, row=9, span=2}{2 - Data Link}

\end{tcbposter}

\end{document}

Answer 5

Thank to @Ignasi who pointed out the tcolorbox package, here is another solution with the raster functionality.

\documentclass[12pt, a4paper]{article}
\usepackage{tcolorbox}
\tcbuselibrary{most, raster}

\begin{document}
    \tcbset{size=small, colframe=red!50!black, colback=red!10!white, raster equal height=rows ,halign=center, valign=center}
    \begin{tcbitemize}[raster columns=3]
        \tcbitem A1
        \tcbitem A2gq
        \tcbitem A3
    \end{tcbitemize}
    \begin{tcbitemize}[raster columns=4, colframe=blue!50!black, colback=blue!10!white]
        \tcbitem B1
        \tcbitem B2
        \tcbitem B3gq
        \tcbitem B4
    \end{tcbitemize}
    \begin{tcbitemize}[raster columns=3]
        \tcbitem C1
        \tcbitem C2gq
        \tcbitem C3
    \end{tcbitemize}
\end{document}