Design a scalable key-value configuration service

Q: Design a scalable key-value configuration service

This question evaluates expertise in distributed systems and system design, testing competencies in schema and API design, partitioning/sharding, storage engine trade-offs, consistency and replication strategies, and operational features like watches, TTLs, backups, and capacity planning within a multi-region key–value configuration service.

Q: How do I approach System Design interview questions?

System Design questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master system design interviews.

Q: What difficulty level is this interview question?

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

Q: What role is this question designed for?

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

Question

Design a Globally Distributed Key–Value Configuration Service

Background

You are asked to design a globally distributed key–value configuration service powering thousands of microservices across multiple regions. The service should provide low-latency reads, strong safety for updates, and global availability.

Requirements

Define the key schema (namespacing, composability, versioning).
Define the value schema (serialization format, validation, schema evolution).
Explain partitioning/sharding, indexing, and storage engine choices (e.g., LSM-tree vs B-tree).
Describe write/read paths and hot-key mitigation.
Specify the consistency model (linearizable vs eventual), leader election, replication/quorums, and handling of network partitions and failover.
Describe support for transactions, watches/subscribe for updates, TTLs, and backup/restore.
Provide capacity planning, SLAs, multi-region replication strategy, and testing approaches.

Assumptions

Read-heavy (≫95% reads), small values (0.5–8 KB), small key space (≤ few million keys), but very high fanout of clients.
Writes are rare but correctness-critical; clients expect fast propagation of changes.
Multi-tenant namespaces, multi-region footprint, thousands of services, tens of thousands of instances.

Design a scalable key-value configuration service

Quick Overview

Design a Globally Distributed Key–Value Configuration Service

Background

Requirements

Assumptions

Solution

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