tex: add stuff on app architecture

tex/text.tex

@@ -792,6 +792,26 @@ official formatting standards.
 
 \n{1}{Application architecture}
 
+The source code is split into Go \emph{packages} appropriately along a couple
+of domains: logging, core application, web routers, configuration and settings,
+etc. In Go, a package is delimited by folder structure -- each folder is a
+package.
+
+Generally speaking, the program aggregates decision points into central places,
+such as \texttt{run.go}, which imports child packages that facilitate each of
+loading the configuration, connecting to the database and running migrations,
+consolidating flag, environment variable and configuration-based values into
+canonical \emph{settings}, setting up routes and handling graceful shutdown.
+
+The program uses dependency injection to share a single logger instance,
+similar applies to the database client. These are passed around as a pointer,
+so the underlying data stays the same. As a rule of thumb, every larger
+\texttt{struct} that needs to be passed around is passed around as a pointer.
+
+Authentication logic is relatively simple and the author would like to isolate
+it into a custom \emph{middleware} but that is a future work.
+
+
 \n{1}{Implementation}
 
 \n{2}{Configuration}