Design and implement a consistent-hashing based router that maps arbitrary keys to backend servers. Requirements: ( 1) Describe the hash ring, token assignment, and use of virtual nodes to smooth load; ( 2) Support addServer(id, weight) and removeServer(id) with minimal key movement; ( 3) Implement getServer(key) and explain the expected percentage of keys that move when servers join/leave; ( 4) Extend to replicate each key to R distinct servers and discuss read/write semantics under failures; ( 5) Analyze time/space complexity and storage overhead.

This question evaluates understanding of consistent hashing, replica placement, dynamic membership, weighted load distribution, rebalancing impact, and related distributed-systems competencies for routing and sharding.

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This is a hard difficulty System Design question, commonly asked during Onsite rounds at DoorDash.

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This question is commonly asked for Software Engineer candidates at DoorDash during technical interviews.

Design consistent hashing for sharding | DoorDash Interview Question

Design a Consistent-Hashing Router with Replication

You are building a stateless router that maps arbitrary keys (for example, request IDs or cache keys) to backend servers. The router must support dynamic membership, weighted capacity, and multi-replica placement while minimizing key movement when servers join or leave.

Requirements:

Hash Ring and Load Smoothing
- Describe the consistent-hash ring, token assignment, and how virtual nodes (vnodes) smooth load imbalance.
Membership Operations
- Provide addServer(id, weight) and removeServer(id) that change as few key-to-server assignments as possible.
Key Lookup and Rebalancing Impact
- Implement getServer(key) and explain the expected percentage of keys that move when servers join or leave (both equal-weight and weighted cases).
Replication to R Distinct Servers
- Extend the design to place each key on R distinct servers and discuss read/write semantics and client behavior under server failures.
Complexity and Overhead
- Analyze time complexity, space complexity, and storage/replication overhead. Include any operational guardrails or validation strategies you would use.

Design a Consistent-Hashing Router with Replication

Requirements:

Hash Ring and Load Smoothing

Describe the consistent-hash ring, token assignment, and how virtual nodes (vnodes) smooth load imbalance.

Membership Operations

Provide addServer(id, weight) and removeServer(id) that change as few key-to-server assignments as possible.

Key Lookup and Rebalancing Impact

Implement getServer(key) and explain the expected percentage of keys that move when servers join or leave (both equal-weight and weighted cases).

Replication to R Distinct Servers

Extend the design to place each key on R distinct servers and discuss read/write semantics and client behavior under server failures.

Complexity and Overhead

Analyze time complexity, space complexity, and storage/replication overhead. Include any operational guardrails or validation strategies you would use.

Design consistent hashing for sharding

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Design a Consistent-Hashing Router with Replication

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Design consistent hashing for sharding

Quick Overview

Design a Consistent-Hashing Router with Replication

Solution

Comments (0)