% Tikz File mqtt_pub_sub.tex
\documentclass{standalone}
\usepackage{tikz}
\usepackage{graphicx}

\begin{document}
\begin{tikzpicture}
    %\draw[help lines] (-7,-5) grid (7,5);

    \pgfmathsetmacro\pub{-4};
    \pgfmathsetmacro\bro{0};
    \pgfmathsetmacro\sub{4};
    \pgfmathsetmacro\y{4};
    
    \draw[ultra thick] (\pub,\y/2) -- (\pub,\y/-2);
    \draw[ultra thick] (\bro,\y/2) -- (\bro,\y/-2);
    \draw[ultra thick] (\sub,\y/2) -- (\sub,\y/-2);
    
    \draw[ultra thick, ->] (\sub,1) -- (\bro, 1);
    \draw[ultra thick, <-] (\sub,-1) -- (\bro, -1);
    \draw[ultra thick, ->] (\pub,0) -- (\bro, 0);
    
    \node at (\pub, \y/2+0.2) {Publisher};
    \node at (\bro, \y/2+0.2) {Broker};
    \node at (\sub, \y/2+0.2) {Subscriber};
    
    \node at (\sub/2, 1.2) {Subscribe (topic)};
    \node at (\pub/2, 0.2) {Publish (topic, info)};
    \node at (\sub/2, -0.8) {Publish (topic, info)};
    
\end{tikzpicture}
\end{document}