Simple Communication Diagram with LaTeX

diagram.tex

\documentclass{standalone}

\usepackage{tikz}
\usepackage{transparent}
\usepackage{fontspec}
\usepackage{xcolor}
\usepackage{graphicx}
\usepackage{anyfontsize}

\usetikzlibrary{calc, backgrounds, positioning, matrix}

\newcommand{\layer}[3]{
  \node[draw] (top) at (#1, #2) {#3};
  \node[draw] (bottom) at (#1, 0) {#3};
  \draw (top.south) -| (bottom.north);
}

\newcommand{\arrow}[5]{
  \draw[-stealth] (#1, #3) -- (#2, #3) node [#5] {#4};
}

\newcommand{\arrowstream}[6]{
  \draw[-stealth, dotted] (#1, #3) -- (#2, #4) node [#6] {#5};
}

\definecolor{foreground}{RGB}{149, 149, 159}
\definecolor{background}{RGB}{41, 42, 45}

\begin{document}
\begin{tikzpicture}[
  draw=foreground, text=foreground,
  label/.style={pos=0.5,above,font=\tiny, sloped}
]
  \newcommand{\height}{5};

  \newcommand{\webui}{0};
  \newcommand{\gitops}{5};
  \newcommand{\mngc}{10};
  \newcommand{\leafca}{15};

  \layer{\webui}  {\height}   {Web UI};
  \layer{\gitops} {\height}   {Backe-end};
  \layer{\mngc}   {\height}   {Agent};
  \layer{\leafca} {\height}   {Cluster};

  \arrow{\webui}{\gitops}{4}{List all Releases}{label};
  \arrowstream{\gitops}{\webui}{1}{0.5}{Stream}{label};

  \arrow{\gitops}{\mngc}{3.5}{List all Releases} {label};

  \draw[dotted] (\mngc, 2.75) -- (7.5, 2.75);
  \draw[dotted] (7.5, 2.75) -- (7.5, 1)
    node [label, rotate=180] {Stream};
  \arrowstream{7.5}{\gitops}{1}{1}{}{};

  \arrow{\mngc}{\leafca}{3}
    {List all Releases}{label};

  \draw[dotted] (\mngc, 2.5) -- (7.5, 2.5);

  \arrowstream{\leafca}{\mngc}{2.5}{2.5}
    {List of events (Releases)}{label};

  \arrowstream{\leafca}{\mngc}{2}{2}
    {New events (Release)}{label};

  \arrowstream{\leafca}{\mngc}{1.5}{1.5}
    {New events (Release)}{label};

  \draw[dotted] (\mngc,2) -- (7.5, 2);
  \draw[dotted] (\mngc,1.5) -- (7.5, 1.5);

  % Add a bit of margin ;)
  \node[yshift=1em, xshift=-2em] at (0, \height) {};
  \node[yshift=-1em, xshift=2em] at (\leafca, 0) {};

\end{tikzpicture}
\end{document}

With my "template" structure: https://gist.github.com/yitsushi/39c544191c58e1b41abce60bff9c7ef4