Design a Robust Feature Flag Evaluation Engine

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Quick Overview

Design a feature-flag evaluator for one or all flags, with ordered conditions, deterministic percentage rollout, defaults, validation, and a true-wins policy. Define operator and null behavior, keep inputs immutable, test conflicting rules and rollout boundaries, diagnose stale fixtures, and consider cache freshness, compatibility, and safe telemetry.

Design a Robust Feature Flag Evaluation Engine

Company: Cresta

Role: Software Engineer

Category: Software Engineering Fundamentals

Difficulty: medium

Interview Round: Onsite

Overview: Design a feature-flag evaluator for one or all flags, with ordered conditions, deterministic percentage rollout, defaults, validation, and a true-wins policy. Define operator and null behavior, keep inputs immutable, test conflicting rules and rollout boundaries, diagnose stale fixtures, and consider cache freshness, compatibility, and safe telemetry.

Read the full Cresta Software Engineer interview experience this question came from

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Cresta
Jul 24, 2026
mediumSoftware EngineerOnsiteSoftware Engineering Fundamentals
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