How to draw Architecture diagram with boxes using simple TikZ code?

Question

I want to draw architecture diagram in latex as in image below

So I tried with simple TikZ code as below

\documentclass[border=3mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{positioning,matrix,shapes.arrows}

\tikzset{
  modulematrix/.style={draw=blue!50!red,rounded corners,matrix of nodes,row sep=1cm,column sep=1cm,nodes={draw=green!70,align=center,font=\sffamily},inner ysep=0.5cm},
  module/.style={rounded corners, align=center, font=\sffamily, thick},
  simple module/.style={module, top color=blue!10, bottom color=blue!35, draw=blue!75, text width=40mm, minimum height=15mm},
  module down arrow/.style={module arrow, shape border rotate=-90},
  module right arrow/.style={module arrow},
module arrow/.style={single arrow, single arrow head extend=2.5mm, draw=gray!75, inner color=gray!20, outer color=gray!35, thick, shape border uses incircle, anchor=tail,minimum height=0.7cm},
}
\begin{document}
\begin{tikzpicture}
\node [simple module] (mA) {Item-1};
\matrix[modulematrix,below=of mA,label={[anchor=south]below:Item-2}] (mB) {Item-3 & Item-4 \\};
\matrix[modulematrix,right=of mB,nodes={text width=5cm,align=center},label={[anchor=north]above:Module C}] (mC) {Item-5 \\ Item-6 \\};
\matrix[modulematrix,below=of mC,label={[anchor=south]below:Item-9}] (mD) {Item-7 & Item-8 \\};

\foreach \n in {mA,mC-1-1,mC,mD}
  \node[module down arrow,below=1mm of \n] {};

\foreach \n in {mB-1-1,mB,mD-1-1}
  \node[module right arrow,right=1mm of \n] {};
\end{tikzpicture}
\end{document}

But I couldn't modify the code as per my expected architecture diagram. So please anyone guide me to modify the code to get my expected diagram.. Thanks in advance..

Answer 1

Fot this scheme, there's no need for matrix nodes, just some regular nodes placed with positioning library and some fit nodes will solve the problem.

Here is my code with some comments inside:

\documentclass[border=3mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{positioning,fit,arrows.meta,backgrounds}

\tikzset{
    module/.style={%
        draw, rounded corners,
        minimum width=#1,
        minimum height=7mm,
        font=\sffamily
        },
    module/.default=2cm,
    >=LaTeX
}

\begin{document}
\begin{tikzpicture}[
    % This will show the frame around the figure
    show background rectangle]

    % Place first 6 items
    \node[module] (I1) {Item-1};
    \node[module, below=of I1] (I2) {Item-2};
    \node[module, below=of I2] (I3) {Item-3};
    \node[module=1cm, below=8mm of I3] (I5) {Item-5};
    \node[module=1cm, left= 3mm of I5] (I4) {Item-4};
    \node[module=1cm, right= 3mm of I5] (I6) {Item-6};
    % Inner box around Items 3-6
    \node[fit=(I3) (I4) (I6), draw, inner sep=2mm] (fit3) {};
    % Outer box around all left items
    \node[fit=(fit3) (I1), draw, inner sep=2mm] (fit1) {};
    % Connections
    \foreach \i in {4,5,6}
        \draw[->] (I3)--(I\i);
    \draw[->] (I2)--(I1);
    \draw[->] (I2)--(fit3);

    % Items 7-8-9. Item 7 as label of Item-8
    \node[module, right=2cm of {I2-|fit1.east}, 
        label={[yshift=5mm, font=\sffamily]Item-7}] 
        (I8) {Item-8};
    \node[module, below=of I8] (I9) {Item-9};
    %outer box around items 8-9
    \node[fit={(I9) (I9|-fit1.south) (I9|-fit1.north)}, draw, inner xsep=5mm, inner ysep=-\pgflinewidth] (fit8) {};

    %arrow between boxes
    \draw[<->,dashed] (fit1)--(fit8);

    %upper label
    \path (fit1.north east)--node[above=3mm, font=\sffamily\bfseries] (arc) {Architecture} (fit8.north west);

\end{tikzpicture}
\end{document}