Fault Tolerance: Redundancy, Replication, and Checkpointing

Learning Objectives Define fault tolerance and differentiate between redundancy, replication, and checkpointing. Analyze a system design to identify single points of failure (SPOFs). Compare and contrast active and passive replication strategies, evaluating their respective trade-offs. Explain the process of system recovery using checkpoints and transaction logs. Apply the N+1 redundancy principle to design a basic fault-tolerant system. Evaluate the performance trade-offs associated with different checkpointing frequencies. Ever wonder why Netflix or your favorite online game rarely goes down, even when servers must fail somewhere? 🎮 Let's explore the magic that keeps these massive systems running. This lesson dives into fault tolerance, the art of building systems t...

TermDefinitionExample Fault ToleranceThe property that enables a system to continue operating properly in the event of the failure of some of its components.A RAID 1 disk array in a server. If one hard drive fails, the system continues to run using the mirrored data on the second drive, with no data loss or downtime. RedundancyThe intentional duplication of critical components or functions of a system with the intention of increasing reliability.An airplane having multiple engines. If one engine fails, the others can provide enough thrust to land the plane safely. ReplicationA specific form of redundancy where entire components (like databases or servers) are duplicated to provide failover capabilities and improve performance.A primary database server has two replica (secondary) servers....

N+1 Redundancy Pattern For a system requiring 'N' components to operate, provide 'N+1' components. This is a common, cost-effective strategy for providing fault tolerance. The '+1' component is a standby or spare that can take over immediately if one of the 'N' active components fails. It protects against a single component failure. Active vs. Passive Replication Active Replication: All replicas process requests concurrently. Passive Replication: Only the primary processes requests; state is copied to passive secondaries. Use Active Replication (also called state machine replication) when you need instantaneous failover and can manage the complexity of keeping all replicas perfectly in sync. Use Passive Replication (also called primary...