u/CorrectHornet4939

Stumbled into making this as a side experiment in long-form cinematic animation - a 2-minute short told entirely in side profile, side scroll.

Pacific Theater, 1943. A B-17 is heading home from a coastal recon mission. Two engines are coughing fuel vapor, the radio's been dead since dusk and a tropical storm is closing in across ten thousand feet of jungle.

It's about flight, weather, fuel and the quiet kind of courage ..

Pub sub comes up in almost every system design interview that involves async processing, event streaming, or decoupling services. Most people can name Kafka and stop there, which is not enough once the interviewer starts asking how partitions get assigned or what happens when a broker dies.

Put together a breakdown of what interviewers actually expect you to cover:

Producer, broker, consumer and how the three roles fit together

Inside the broker: a small control plane and a huge append only log

Why a log beats a queue: offsets, replay, fan out

Topics split into N partitions for throughput

Hash the key, modulo N, pick the partition, with a worked example

Replication with 3 replicas across 3 zones, one leader and two followers

Leader failover when the leader dies

Consumer groups and how partitions get split across consumers

The controller or ZooKeeper heartbeating every broker

At most once vs at least once vs exactly once delivery

If you can draw partition routing, name the failure modes, and pick the right delivery semantic, you come across as senior. Skip the controller story and the interviewer will keep probing

Most people can say sharding splits data across machines but freeze when asks how you pick the shard, what happens when you add a node, or how the cluster knows who the leader is.

Put together a breakdown of what it actually expect you to cover:

Vertical vs horizontal sharding

Range vs hash partitioning

The hash modulo N trap and why adding one server reshuffles everything

Consistent hashing on a ring, where only the neighbor's keys move

Virtual nodes for handling hot shards and rebalancing

Hierarchical sharding for region and zone isolation

Local vs global secondary indexes

Leader follower replication and master failover

ZooKeeper, etcd, and Consul as the cluster oracle

Why sharding should always be the last resort

DNS comes up constantly in system design interviews, especially for any question involving global traffic, CDNs, or low latency. Most people can say it turns names into IPs and stop there, which is not enough if the interviewer pushes.

Put together a breakdown of what interviewers actually expect you to cover:

Why computers need IP addresses but humans need names

The 5 hop journey: browser cache, ISP resolver, root, TLD, authoritative server

Why a cache hit is around 40 times faster than a miss

The DNS record types worth knowing: A, AAAA, CNAME, MX, TXT, NS

How to read a domain name right to left

If you can walk through the 5 hops and explain the caching at each layer, you come across as senior

Caching is one of those topics that comes up in almost every system design interview, but most people only know cache aside and freeze when the interviewer pushes further.

Put together a breakdown of what interviewers actually expect you to cover:

Where caching can live: client, CDN, application server, external cache

The 4 architectures: cache aside, write through, write behind, read through

The 4 eviction policies: LRU, LFU, FIFO, TTL

The 3 problems caching introduces: thundering herd, stale reads, hot keys

A 5 step framework for walking through it on the whiteboard

If you can hit all 5 steps you come across as senior. Skip the last one and the interviewer will keep probing

MO theory is not heavy on the AP exam but it shows up enough that having the visual intuition helps and it makes Lewis structures and bond order questions way easier to reason about.

This is a video that builds it up in 3D from the wave nature of orbitals. Covers constructive and destructive interference between two 1s orbitals, the bonding sigma and antibonding sigma star with the node, the MO energy diagram drawn step by step and the bond order formula.

Worked examples for H2 (bond order one, stable) and He2 (bond order zero, does not exist) and a quick comparison of H2, O2, and N2 bond orders that explains why nitrogen is so hard to break

Acids and bases questions come up here a lot so figured this might save some people time.

It Covers the pH scale 0 to 14 and why each step is 10x stronger, what acids actually do (release H+ ions in water), what bases do (release OH- ions), neutralization shown with HCl plus NaOH making salt and water in 3D and the strong acids and bases worth knowing

a lesson on atomic structure aimed at students who find textbook diagrams hard to picture. Sharing in case it is useful for your classes or as a flipped-classroom assignment.

What it covers:

Protons, neutrons, electrons, their relative mass and charge, why atoms are mostly empty space, how neutral atoms balance, ions and the charge flip, reading nuclear symbols, isotopes, and a worked example calculating relative atomic mass for copper from its two isotopes.

Everything is rendered in 3D with color-coded particles so students can see the nucleus and electron shells as actual objects rather than flat circles. Pacing is slow and nothing is skipped, so it works for students who are seeing this for the first time. Roughly GCSE through early AP Chem level.