Fault Tolerance

What are Raft and Paxos? Consensus Algorithms Explained

Raft and Paxos are consensus algorithms that let a group of distributed nodes agree on a single value or an ordered sequence of operations even when some nodes…

What Are Database Failover Mechanisms and How Do They Work?

Database failover is the mechanism by which a standby or replica database automatically (or manually) takes over as the primary when the original primary becom…

How Do You Design a Robust Database Health Check?

A robust database health check goes beyond a simple TCP ping by verifying that the database can actually execute a real query within an acceptable time, checki…

What are RAID Levels and How Do They Differ?

RAID (Redundant Array of Independent Disks) combines multiple physical disks into one logical unit using striping, mirroring, or parity, and different RAID lev…

What is a Distributed File System?

A distributed file system presents files stored across multiple networked machines through a single unified namespace, so clients read and write remote files u…

How Does Distributed Mutual Exclusion Work?

Distributed mutual exclusion ensures that only one process across an entire network of machines enters a critical section at a time, achieved without shared me…

What Is a Distributed Operating System?

A distributed operating system manages a collection of independent, networked computers and presents them to users and applications as a single coherent system…

What are Network Topologies? Star, Bus, Ring, and Mesh Explained

A network topology is the physical or logical arrangement of how devices are connected to each other in a network — the most common patterns are bus (a single…

What is Health Checking in Networking?

Health checking is the process by which a load balancer or orchestrator periodically probes each backend server — via TCP connect, HTTP request, or a custom pr…

Horizontal vs Vertical Scaling

Vertical scaling (scaling up) means adding more power — CPU, RAM or disk — to a single machine, while horizontal scaling (scaling out) means adding more machin…

What is Database Replication in System Design?

Database replication is the process of copying data from a primary database to one or more replica databases so the system gains redundancy for fault tolerance…

What is a Single Point of Failure (SPOF)?

A single point of failure (SPOF) is any component in a system whose failure alone causes the entire system, or a critical part of it, to become unavailable, an…

How to Design a Distributed File System

A distributed file system splits large files into fixed-size chunks replicated across many storage nodes, with a separate metadata service tracking which chunk…

How Would You Design a Distributed Job Scheduler?

A distributed scheduler is a system that reliably triggers jobs at the right time across a fleet of worker nodes, using a durable job store, a leader-elected t…

How to Design a Vending Machine System?

A vending machine system is best modeled as a finite state machine with a small set of explicit states (idle, selecting, awaiting payment, dispensing, returnin…

What is Quorum-based Consensus and How Does It Work?

Quorum-based consensus requires a minimum number of nodes (a quorum) to agree before a read or write is considered successful, typically enforcing that the rea…

What is the Raft Consensus Algorithm?

Raft is a consensus algorithm that lets a cluster of nodes agree on a single, replicated sequence of operations by electing one leader per term who owns all wr…

What is the Paxos Consensus Algorithm?

Paxos is a consensus algorithm that lets a group of nodes agree on a single value even with failures and message loss, using two phases (prepare/promise, then…

How Does Leader Election Work in Distributed Systems?

Leader election is the process by which nodes in a distributed cluster agree on a single node to coordinate a particular task, using a protocol (often built on…

What is Two-Phase Commit (2PC)?

Two-phase commit (2PC) is a distributed transaction protocol where a coordinator asks every participant to vote on whether it can commit a transaction (the pre…

What is the Circuit Breaker Pattern?

The circuit breaker pattern wraps a call to a remote dependency with a state machine that stops sending requests to a service once it detects repeated failures…

What is Retry with Exponential Backoff?

Retry with exponential backoff is a strategy for re-attempting a failed request after progressively longer wait times between each retry, often with added rand…

What Do "Nines" of Availability Mean?

"Nines" of availability refer to the percentage of time a system is operational, expressed as a count of 9s — three nines (99.9%) allows about 8.77 hours of do…

How Do You Design a Multi-Region Deployment?

A multi-region deployment runs a system's services and data across geographically separate cloud regions, typically to cut latency for global users and to surv…