A search autocomplete system provides real-time suggestions as users type, ranking completions by popularity or relevance. At Google or Amazon […]

A file storage system (like Dropbox or Google Drive) stores user files, provides sync across devices, and handles concurrent edits.

A notification system delivers messages to users through one or more channels — push notifications, email, SMS, in-app. At scale

A URL shortener converts a long URL into a short alias (e.g., bit.ly/abc123) that redirects to the original. Building one

A time series database (TSDB) is optimized for storing and querying time-stamped data — metrics, sensor readings, financial prices, event

Real-time server-to-client communication requires the server to push data without waiting for a client request. Three primary patterns exist: long

The gossip protocol (epidemic protocol) is a peer-to-peer communication method where each node periodically shares information with a small number

Observability is the ability to understand the internal state of a system from its external outputs. A system is observable

Exactly-once delivery means that every message is processed precisely once — neither lost (at-least-once) nor delivered multiple times (at-most-once). True

Raft is a distributed consensus algorithm designed to be understandable — a deliberate contrast to Paxos, which is notoriously difficult

Backpressure is a mechanism that allows a downstream component to signal an upstream component to slow down — preventing fast

API versioning allows a service to evolve its interface without breaking existing clients. The fundamental challenge: once an API is

The Saga pattern is a way to manage data consistency across multiple services in a microservices architecture without using distributed

A Merkle tree is a hash tree where every leaf node contains the hash of a data block, and every

A skip list is a probabilistic data structure that provides O(log n) average time for search, insertion, and deletion —