System Design Glossary

An API gateway is a server that acts as a single entry point for a set of microservices, handling request routing, authentication, rate limiting, and protocol translation.

Blob storage (Binary Large Object storage) is a cloud service for storing massive amounts of unstructured data like images, videos, documents, and backups, optimized for high availability and scalable access.

A CDN is a geographically distributed network of servers that caches and delivers content from locations close to end users, reducing latency and improving load times.

Caching is the technique of storing copies of frequently accessed data in a faster storage layer so that future requests can be served more quickly, reducing latency and load on the primary data source.

Consistent hashing is a distributed hashing technique that minimizes the number of keys that need to be remapped when the number of nodes in a system changes, making it ideal for distributed caches and databases.

The CAP theorem states that a distributed data system can simultaneously provide only two of three guarantees: Consistency (all nodes see the same data), Availability (every request receives a response), and Partition tolerance (the system operates despite network failures).

A circuit breaker is a design pattern that prevents an application from repeatedly trying an operation that is likely to fail, allowing the system to fail fast and recover gracefully instead of cascading failures.

CQRS is an architectural pattern that separates read operations (queries) from write operations (commands) into different models, allowing each to be optimized, scaled, and evolved independently.

Database sharding is a horizontal partitioning strategy that splits a large database into smaller, independent pieces called shards, each stored on a separate server to distribute load and improve performance.

Database replication is the process of copying and maintaining database objects across multiple servers, providing redundancy for fault tolerance and enabling read scaling by distributing queries across replicas.

A database index is a data structure that improves the speed of data retrieval operations on a table at the cost of additional storage space and slower writes, functioning like a book's index for quick lookups.

Event-driven architecture is a design pattern where system components communicate by producing and reacting to events, enabling loose coupling, real-time processing, and independent scaling of services.

Horizontal scaling (scaling out) means adding more machines to a system to handle increased load, distributing work across multiple servers rather than upgrading a single machine.

A heartbeat is a periodic signal sent between distributed system components to indicate they are alive and functioning, used for failure detection and triggering recovery mechanisms when signals stop.

A load balancer distributes incoming network traffic across multiple servers to ensure no single server is overwhelmed, improving availability and responsiveness of applications.

Leader election is a distributed algorithm by which nodes in a cluster designate one node as the leader responsible for coordinating actions, ensuring that exactly one node makes decisions at any given time.

Long polling is a technique where the client makes an HTTP request and the server holds the connection open until new data is available or a timeout occurs, simulating real-time server push over standard HTTP.

Latency is the time delay between a user action (or request) and the system's response, typically measured in milliseconds. It is a critical non-functional requirement in system design that directly impacts user experience.

A message queue is a communication mechanism that enables asynchronous data exchange between services by storing messages in a queue until the receiving service is ready to process them.

Microservices is an architectural style where an application is composed of small, independently deployable services, each running in its own process and communicating via lightweight protocols like HTTP or messaging.

Pub/Sub is a messaging pattern where publishers send messages to topics without knowledge of subscribers, and subscribers receive messages from topics they are interested in, enabling loosely coupled communication.

A reverse proxy is a server that sits in front of backend servers and forwards client requests to them, providing load balancing, caching, SSL termination, and security benefits.

Rate limiting controls the number of requests a client can make to a service within a given time window, protecting systems from abuse, preventing resource exhaustion, and ensuring fair usage across users.

SQL databases store data in structured tables with predefined schemas and support ACID transactions, while NoSQL databases use flexible data models (document, key-value, column-family, or graph) optimized for specific access patterns and horizontal scaling.

Vertical scaling (scaling up) means increasing the resources of a single machine — adding more CPU, RAM, or storage — to handle increased load, as opposed to adding more machines.

WebSockets provide a persistent, full-duplex communication channel over a single TCP connection between a client and server, enabling real-time bidirectional data transfer without the overhead of repeated HTTP requests.