Stop 08 · Technical Fluency for PMsTopics · 4/11

System Design Basics for PMs

In short

You won't design the system, but you'll sit in the review. Knowing what a load balancer, cache or queue does lets you ask the questions that matter for users.

A light version of what engineers study deeply — knowing terms like load balancer, cache, and database replica well enough to follow (and question) an architecture discussion.

The purple blob directs a long queue of travellers towards several open ticket counters.

Think of it like this

The busy station hall

At a big station, a staff member directs the queue to whichever counter is free. A board shows train timings so nobody asks the same question again. That's a load balancer and a cache, in a ticket hall.

Watch it happen

One request through a typical setup

User

Load balancer

App server

Cache

GET /menu

1/5The request first hits a load balancer, which spreads traffic across many servers.

The big ideas

What you need to know

Load balancer

Spreads requests across servers so no single one is overloaded.

Cache

Keeps frequently read data in fast memory. Trade-off: users may briefly see stale data.

Queue

Holds slow jobs, like sending emails, so the user doesn't wait for them.

Replicas

Copies of the database. Reads spread out, and one copy can take over if another fails.

Save yourself the pain

Common mistakes

Oops

Asking for real-time data everywhere.

Do this instead

Ask how fresh each screen really needs to be. A minute-old cache is fine for many cases.

Oops

Nodding along when you don't understand a diagram.

Do this instead

Ask "what happens to the user if this box fails?" It's the most useful PM question.

Your mission

Draw a simple system

~30 min

Quick check

Why might a team put a restaurant menu in a cache?

Go deeper

1Watch a beginner-friendly system design explainer video (many free ones exist).
2Learn what a cache is for, in plain language, and why it can serve stale data.
3Practice asking 'what happens if this fails?' in an architecture conversation.