Three-tier web app
Browser → web → app → DB, positioned with Pikchr's relative coords.
Rendering…
Make it your own.
B: box "Browser" rad 5px
arrow ">"
W: box "Web tier"
arrow ">"
A: box "App tier"
arrow ">"
D: cylinder "Postgres" fit
move right 0.4
arrow from W.s to A.n dashed "session"