distributed systems

When you shard a vector index or route requests across model replicas, naive 'hash mod N' reshuffles everything when N changes. Consistent hashing moves only a small fraction. Here is the implementation.

Anthropic's signature opener. The naive answer (one server pushes to N clients) is bottlenecked by the source uplink and scales linearly. The answer interviewers reward turns receivers into senders so the swarm's capacity grows with its size. Here is that reasoning.

The Dynamo question. Interviewers want three decisions made cleanly: how you partition keys so adding nodes does not reshuffle everything, how you replicate for durability, and where you land on the CAP spectrum. Here is how to reason about all three with concrete quorum math.

Every API platform needs one. Interviewers reward the candidate who picks the right algorithm (token bucket vs sliding window) for the burst behavior, then solves the genuinely hard part: enforcing one shared limit across many servers without a per-request round trip to a central store.

Looks simple until the follow-ups: which layer do you balance at, how do you avoid sending traffic to a dead server, and how is the load balancer itself not a single point of failure? Interviewers want the algorithm, the health-check loop, and the high-availability story.

A deceptively rich warm-up. The interesting decisions are how you generate short, collision-free, unguessable keys at scale, and how a read-heavy 100:1 workload shapes the storage and caching. Here is the clean design with capacity math.

The observability infrastructure question. Interviewers want you to separate the three telemetry types, choose storage that survives massive write volume, and design alerting that fires fast without drowning on-call in noise. Here is the pipeline with retention and cardinality math.

The distributed ordering question, the conceptual core of Kafka, replicated logs, and consensus systems. Interviewers want to see you confront the hard truth that physical clocks lie, then reach for the actual tools: a single sequencer, consensus, or logical clocks. Here is that progression.

The real-time messaging classic. Interviewers want the delivery path (persistent connections, not polling), the fan-out strategy that does not collapse on large groups, and an ordering and delivery-guarantee story. Here is that design with the fan-out tradeoff that separates seniors.