Search the practice set
275 questions, 991 terms and 600 topics in 30 areas.
60 results for “Client Feature Flags”
Flag Evaluation Latency
The delay between page load and the client knowing which variant to show, which produces a visible flicker unless the flag is resolved before render.
Flag Debt
The accumulating complexity of feature flags that are never removed, producing untested code paths and combinatorial behaviour nobody understands.
Client Runtime Constraint
The properties of the browser or device you do not control — CPU, network, version, extensions — which make the client a distributed system component rather than a rendering surface.
Client-Side Discovery
The caller queries the registry itself and chooses an instance, rather than sending to a stable address that something else resolves.
Client-Specific Aggregation
A dedicated backend per client type that shapes and combines downstream data for that client's needs, owned by the client team.
Feature Criticality Tiering
Classifying product functionality by whether it must work, should work, or can be dropped, so degradation decisions are made in advance by the business.
Feature Flag
A runtime switch that decouples deploying code from releasing behaviour, so unfinished or risky work can ship dark.
Feature Parity Trap
The expectation that a replacement system must match every behaviour of the old one before it can be adopted, which is what makes rewrites never finish.
Feature Staleness
The age of the feature values a model scores against, and the divergence between how they are computed at training time and at inference time.
Feature Store
A system that computes, stores and serves model input features consistently for both training and inference, eliminating training-serving skew.
Anycast
Advertising the same IP address from many locations, so the network routes each client to the topologically nearest one.
Authorization Code Flow with PKCE
The OAuth flow recommended for all client types, in which an authorisation code is exchanged for tokens using a proof key that binds the exchange to the original requester.
Backend for Frontend
A separate, narrow backend per client experience, which aggregates and reshapes downstream services for exactly that client's needs.
Booking.com's Experimentation Platform
Booking.com runs over a thousand concurrent experiments and treats the ability to test any change safely as a platform capability rather than a product feature.
Build vs Buy
The choice between developing a capability in-house and acquiring it, decided on differentiation and total cost rather than on feature lists.
Certificate Chain
The sequence from a server's certificate through one or more intermediate CAs to a root the client already trusts.
Connection Proxy
A pooling layer between applications and a managed database that multiplexes many client connections onto a small number of database connections.
Error Budget
The amount of unreliability an SLO permits, treated as a resource that feature velocity spends.
Forced Upgrade
Blocking an installed client version from operating until it updates, which is the only lever available and is disruptive enough to need a policy.
Gateway Aggregation
Combining several backend calls into one client-facing response at the gateway, reducing client round trips at the cost of coupling the gateway to backend structure.
Gateway Timeout Chain
The sequence of timeouts from client through load balancer, gateway and service, which must decrease inward or produce confusing failures.
GraphQL
A query language and runtime where the client specifies exactly which fields it needs, against a typed schema, usually via a single endpoint.
Idempotency Key
A client-generated unique value sent with a request so the server can recognise a retry and return the original result instead of acting twice.
Mutual TLS
TLS in which both ends present certificates, so the server authenticates the client cryptographically rather than by a shared secret.
Non-Functional Acceptance
Treating quality-attribute targets as acceptance criteria with automated verification, so a release can fail on latency the way it fails on a broken feature.
Read Timeout
The bound on how long a client waits for response data after a connection is established — distinct from the connect timeout, and the one that usually matters.
Read-Your-Writes Consistency
A session guarantee that a client always sees its own updates, even when reads are served from replicas that may lag.
Retry-After
A response header telling a client how long to wait before retrying, turning a rejection into actionable guidance.
Retryable Error
An error whose cause may resolve on its own, which a client may safely attempt again — as distinct from one that will fail identically.
Reverse Proxy
A server that receives client requests on behalf of one or more backends, forwarding them and returning the response.
A codebase has 340 feature flags, most of them permanently on. What is the problem and how do you fix it?
The problem is combinatorial and it is not theoretical Every flag doubles the number of possible code paths. At 340, the number of configurations is unbounded a
Knight Capital lost roughly $460M in 45 minutes in 2012 after a deployment reached seven of eight servers. Which architectural failures made that possible, and which one would you fix first?
The case, as publicly reported Per the SEC's 2013 order, Knight Capital deployed new order routing code to eight production servers ahead of a NYSE programme la
A 15-year-old monolith must be modernised without a rewrite and without a feature freeze. Plan the migration.
Establish why, before deciding what "Modernise" is not an objective. The reasons that justify the cost are specific: delivery is too slow; the technology is uns
A client wants an assistant that answers questions from 50,000 internal documents which change weekly. RAG or fine-tuning? What actually determines the quality?
What the interviewer is testing Whether you understand what each technique actually does, and whether you know that RAG quality is a retrieval problem. Why RAG
A marketing site is a client-rendered single-page application. Organic traffic is poor and the team blames the search engine. What is your assessment?
The rendering choice is the problem A marketing page is identical for every visitor and highly cacheable. Rendering it in the browser pays for personalisation t
A regulated client requires that no traffic between their data centre and your SaaS platform traverses the public internet. Design the connectivity and justify the cost.
Two distinct requirements hiding in one sentence Traffic must not traverse the public internet — a routing requirement. The client must be able to demonstrate i
A service becomes unresponsive during an incident in a dependency it barely uses. Investigation finds the client had no read timeout. Explain the full mechanism.
The mechanism, step by step 1. The dependency slows. It has not failed — it accepts connections and eventually responds, just very slowly. This is the important
An AI feature launched two months ago now costs more per month than the rest of the platform. What do you investigate?
Get cost per request, decomposed Token cost splits into input and output, and they price differently. Break the bill down by feature, by user, and by input vers
An LLM feature that worked last week now gives worse answers. Nothing was deployed. How do you find out what changed, and what should have been in place?
What the interviewer is testing Whether you treat an AI feature as a system with configuration and dependencies, or as a black box that mysteriously drifts. Wha
Design an order submission API that is safe when the client cannot tell whether its request succeeded. What exactly do you store, and when?
What the interviewer is testing Whether you know that "make it idempotent" is a design with specific failure modes, not a checkbox. The core design The client g
Product wants to add a recommendation feature using browsing history. Legal asks for a data protection impact assessment. What does architecture need to supply?
What the assessment actually needs from architecture Legal cannot assess a feature description. They need the data facts, which only the design supplies: A data
You inherit an IoT fleet of 80,000 devices whose client certificates all expire in fourteen months. What do you do?
Establish whether rotation is even possible The first question is whether the current firmware can obtain and install a new certificate remotely. If it cannot,
Your company needs a feature flag and experimentation platform. A vendor charges a substantial annual fee; a team estimates six weeks to build one. Decide.
Apply the differentiation test first Is this a source of competitive advantage? Feature flagging is context, not core: customers do not choose you for it, and b
A front-end team wants to replace their global state library because "state management is unmanageable". How do you evaluate the request?
Ask what is actually in the store The complaint almost always resolves to one distinction not having been made: server state versus UI state . Server state is d
Customers reported an outage 40 minutes before your monitoring did. How do you close that gap?
What the gap tells you Every technical signal was green while users were failing. That is not a threshold tuning problem; it means the system was monitoring com
Client Feature Flags
Flag evaluation on a device you do not control, and the flicker and staleness it brings.
Feature Flags
Decoupling deploy from release, with an expiry date.
Client Caching & Data Layer
Stale-while-revalidate, invalidation and optimistic updates on the client.
Client State Architecture
Server state, UI state and derived state, and why conflating them causes most bugs.
Feature Freshness
How stale a feature can be before the model degrades, and the pipeline that follows.
API Shapes for UI
REST, GraphQL and RPC judged by over-fetching, round trips and client coupling.
Backend for Frontend
A narrow backend per client experience, owned by that client's team.
Error Budgets
Unreliability as a resource that feature velocity spends.
GraphQL
Client-specified queries, N+1 resolution and query-cost control.
Idempotency
Making an operation safe to repeat, because a client that times out cannot know.
Idempotency Keys
Client-generated keys stored atomically with the operation they guard.
ML Platform
Feature stores, training pipelines, registries and deployment.
Platform Funding
Central cost, showback, chargeback, and justifying a team that ships no customer feature.
Rendering Strategies
Client, server, static and incremental rendering, and what each costs on first paint.