CAP Theorem and Consistency Models Questions

Understand the CAP theorem and how Consistency, Availability, and Partition Tolerance interact in distributed systems. Know different consistency models including strong consistency such as linearizability, eventual consistency, causal consistency, and session consistency, and how to apply them to different use cases. Be familiar with consensus protocols and distributed coordination primitives such as Raft and Paxos, quorum reads and writes, two phase commit and when to use them. Understand trade offs between consistency and availability under network partitions, patterns for hybrid approaches where different data uses different guarantees, and the product and developer experience implications such as latency, stale reads, and API contract clarity.

HardTechnical

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Design a consistency SLA and an error-budget model for a multi-tenant service that allows tenants to choose between strong and eventual consistency tiers. Include how you would measure compliance, bill for stronger guarantees, and throttle tenants to protect the platform.

EasyTechnical

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Explain causal consistency and give a concrete example of how causal ordering matters in a collaborative chat application. Outline an implementation approach (at high level) to preserve causal relationships between operations without enforcing total ordering.

EasyTechnical

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Define 'stale reads' in a replicated system. List three common root causes (e.g., replication lag, caching, read routing) and describe how an SRE can detect and alert on stale reads in production.

HardSystem Design

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Design developer-facing API contracts for a public REST API that exposes eventually-consistent resources. Propose headers or response fields that indicate consistency guarantees and staleness (e.g., version, timestamp, stale=true), and describe how you would document behavioral expectations and migration paths for clients wanting stronger guarantees.

MediumTechnical

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Explain how to tune N, R, and W for a quorum system to balance latency and availability. Describe the impact of (a) increasing N, (b) increasing W, and (c) decreasing R on read/write latency and fault tolerance, and give an example configuration for a geo-replicated store.

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