Question 1

What latency numbers and availability targets should every engineer know?

Accepted Answer

**Target Audience:** Beginners — no hardware or operations background assumed.
**Difficulty:** Easy
**Verified with:** Node 22.22 and Python 3.12 (the calculator prints the same output in both).

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact words an interviewer expects. Every derived number was computed by the example program; the **Verified** section quotes its full output.

## 1. Why This Even Mat

Question 2

How do you design for high availability?

Accepted Answer

**Target Audience:** Beginners to reliability engineering — you know what a server, a load balancer and a database are; every reliability term is defined as we go.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (both print identical output). All component availabilities in the run are stated assumptions, not vendor SLAs; AWS health-check defaults are from the Amazon Route 53 Developer Guide, checked in October 2026.

> **How to read this doc:** Every idea is explained in pl

Question 3

What is the CAP theorem and how does it drive consistency vs availability tradeoffs?

Accepted Answer

# CAP Theorem: Consistency vs. Availability Tradeoffs (Beginner-Friendly Guide)

**Target Audience:** Junior & Senior Software Engineers preparing for System Design Interviews — no prior system design knowledge assumed.
**Difficulty:** Easy to Medium

> **How to read this doc:** Every concept is explained in plain language first. Right after, you'll see a callout like `📌 Interview term:` — that's the exact vocabulary a senior engineer would use for the same idea.

## 1. Why This Even Matters —

Question 4

What is the difference between horizontal and vertical scaling?

Accepted Answer

**Target Audience:** Beginners to system design — you know what a server and a database are, nothing more.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (the example prints the same table in both).

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact words an interviewer expects. Every number below comes from actually running the example program; the **Verified** section quotes its f

Question 5

What is two-phase commit and its drawbacks?

Accepted Answer

**Target Audience:** Developers who know what a database transaction is and now meet data spread over several databases or services. No distributed-systems background assumed.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (both print identical output).

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact words an interviewer expects. All timings and counts come from running the examp

Question 6

What is database replication?

Accepted Answer

**Target Audience:** Beginners to distributed data — you know what a database server is; no prior knowledge of replication assumed.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (both print identical output).

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact words an interviewer expects. Behaviour shown comes from running the example; the **Verified** section quotes the full outpu

Question 7

What are the trade-offs of microservices vs a monolith?

Accepted Answer

**Target Audience:** Beginners to architecture — you have built a web application; every term is defined the first time it is used.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (both print identical output). Hop latencies, availabilities and memory sizes are stated assumptions. The case studies are cited to their published coverage (InfoQ, July 2018, on Segment; DevClass, May 2023, on Prime Video), checked October 2026.

> **How to read this doc:** Plain language first, t

Question 8

What is the difference between strong and eventual consistency?

Accepted Answer

**Target Audience:** Beginners to distributed systems — you know what a database and a replica copy are; everything else is defined as we go.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (both print identical output).

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact words an interviewer expects. Stale-read rates and timings come from the example program; the **Verified** section

Question 9

What is a read/write quorum?

Accepted Answer

**Target Audience:** Beginners to distributed systems who know that databases can keep copies of data on several machines.
**Difficulty:** Medium
**Verified with:** Node 22.22, Python 3.12, Go 1.24 and Java 21 (all four print identical output). Cassandra consistency levels are cited from the DataStax Cassandra documentation; Dynamo techniques from the Dynamo paper (SOSP 2007) as summarised in course material.

> **How to read this doc:** Every idea is explained in plain language first, then tagg

Question 10

How would you design a rate limiter?

Accepted Answer

**Target Audience:** Developers preparing for system design interviews. You know what an API and a load balancer are; the algorithms are covered on sibling pages and only summarised here.
**Difficulty:** Hard
**Verified with:** Node 22.22, Python 3.12, Go 1.24 and Java 21 (all four print identical output). Memory figures were measured on Redis 7.0.15.

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact wo

SYSTEM DESIGNDECODED.

Easy

What latency numbers and availability targets should every engineer know?

Medium

How do you design for high availability?

What is the CAP theorem and how does it drive consistency vs availability tradeoffs?

What is the difference between horizontal and vertical scaling?

What is two-phase commit and its drawbacks?

What is database replication?

What are the trade-offs of microservices vs a monolith?

What is the difference between strong and eventual consistency?

What is a read/write quorum?

Hard

How would you design a rate limiter?

How would you design a URL shortener like TinyURL?

How would you design a distributed message queue?

How would you design a hotel reservation system?

How would you design S3-like object storage?