Search the practice set
275 questions, 991 terms and 600 topics in 30 areas.
60 results for “Control Design vs Operation”
Operating Effectiveness
Whether a control actually ran, consistently, over a period — as distinct from whether it was well designed, and the harder of the two to demonstrate.
Event Notification vs Event-Carried State
Whether an event carries only the fact that something happened, or also the data a consumer needs to act on it.
Fail-Fast vs Fail-Safe
Whether a component should stop immediately on detecting a problem, or continue in a degraded but safe mode — a choice that depends entirely on which outcome is worse.
Managed vs Self-Managed
Trading control, portability and unit cost against the operational burden of running the thing yourself.
Preventive Control Placement
Choosing where in the lifecycle a control acts — at authoring, at admission or after the fact — which determines both its strength and its cost.
Security vs Usability
A trade-off that is usually resolved by varying the control with the value of the action, rather than by choosing a uniform level of friction.
Strong vs Eventual Consistency
A per-operation decision, not a per-system one: whether this specific read must reflect every completed write.
Zonal vs Regional Services
Whether a cloud resource lives in one availability zone or is inherently spread across several — a property that determines what a zone failure takes with it.
Centralisation Trade-off
The exchange between consistency and control gained by centralising a capability and the autonomy and speed retained by distributing it.
Consistency Level Selection
Choosing the consistency guarantee per operation rather than per system, matching the cost of coordination to the business consequence of staleness.
Idempotency
The property that performing an operation many times has the same effect as performing it once.
Immutable Store Erasure Conflict
The direct contradiction between architectures designed never to forget and obligations requiring data to be removed, which must be resolved in the design rather than in policy.
Active-Active vs Active-Passive
Whether all regions serve traffic simultaneously, or one serves while another waits to take over — a choice about which failure mode you would rather have.
Admission Control
Deciding at the edge whether to accept a request at all, based on current capacity, before any work is done on it.
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.
Cache-Control
The HTTP header directing how a response may be cached and for how long, by browsers, proxies and CDNs.
Containment vs Eradication
Stopping an attacker's ongoing access versus removing their foothold entirely — sequential phases with different urgency and different risks of doing them wrong.
Control Plane and Data Plane
The separation between the machinery that makes changes to a system and the machinery that serves its traffic.
Control Test Automation
Executing a control's test continuously against the whole population rather than sampling it annually, which changes both the detection latency and the strength of the evidence.
Cost vs Reliability Trade-off
The non-linear relationship between availability and spend, which makes each additional nine roughly an order of magnitude more expensive.
Credit-Based Flow Control
A scheme where a receiver grants the sender a budget of bytes or messages it may transmit, replenished as the receiver consumes.
Delivery vs Maintainability
Choosing where to take deliberate shortcuts, based on which kinds of debt are cheap to repay and which compound.
Design Review Trigger
The stated conditions under which a change requires security review, so that review capacity goes to what warrants it and everything else proceeds.
A core mainframe system with no API supports nightly batch file exchange only. The business needs near-real-time order status. Design the integration.
Establish the real constraint "No API" usually means no API the mainframe team will build on your timeline . Find out what exists: message queue interfaces, dat
A design review presents a new event-driven platform. What cost questions do you ask before approving it?
What the interviewer is testing Whether cost is part of your architecture review or an afterthought handled by finance later, and whether you know the specific
A payments API must guarantee that a network retry never charges a customer twice. Design the mechanism end to end.
Why this is unavoidable A client that times out on a POST cannot know whether the request succeeded. Not retrying risks a lost payment; retrying risks a duplica
A platform of 40 services has logs only, and incidents take hours to diagnose. Design the observability strategy and its rollout order.
Why logs alone fail at this size Logs answer "what happened in this service". They cannot answer "where did this request spend its time across twelve services",
A product catalogue page does 40,000 reads per second against a database that can serve 5,000. Walk me through the caching design, including what happens at 3 AM when the cache is empty.
What the interviewer is testing Whether you can design a cache including its failure modes, rather than saying "put Redis in front of it". The base design Cache
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 team proposes circuit breakers on every downstream call. What would you add, and why is the breaker not the most important control?
Why the bulkhead matters more A circuit breaker acts after it has detected a pattern of failure. During the seconds before it trips — and while its threshold is
A team shows you a design with eight services. Without knowing the domain, what questions tell you whether the boundaries are right?
What the interviewer is testing Whether you can evaluate a structure from its properties rather than needing to be a domain expert in every system you review. T
A twenty-year-old core system supports most of the business. It is on unsupported technology, three people understand it, and the last replacement attempt was abandoned after two years. Design the programme.
Learn from the abandoned attempt first The most important input is why the last one failed, and the reasons are usually structural rather than technical: a big
An estate has database passwords in environment variables across 200 services. Design the migration to a secrets manager.
Sequence it by risk, not by convenience Phase 0 — stop the bleeding. Secret scanning in CI and on the existing repositories, blocking new commits containing cre
Architecture decisions in your organisation are either ignored or bottlenecked in a review board. Design something better.
Why both failure modes have the same cause A review board is a synchronous, low bandwidth, high latency channel: teams wait, decisions are made by people distan
Classify DynamoDB, Spanner and Cassandra under PACELC, and say which half of the classification you would actually design around.
The classifications Store Partition Else Why DynamoDB (default reads) PA EL Serves from any replica; eventually consistent reads avoid a quorum round trip Cassa
Design a URL shortener handling 100 million new links per month and 10 billion redirects. Where is the real difficulty?
What the interviewer is testing The classic warm up. What is being assessed is not whether you can shorten a URL — it is whether you do capacity arithmetic befo
Design a webhook delivery system for a platform with 10,000 customers. What are the hard parts?
Delivery, and its failure modes Persist the event first, deliver asynchronously. Delivery in the request path couples your latency and availability to every cus
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
Design rate limiting for a multi-tenant API where a single customer's traffic spike currently degrades service for everyone.
Name the problem precisely This is the noisy neighbour problem. Rate limiting is one control for it, and on its own it is incomplete — a customer within their l
Design the audit logging for a system handling financial transactions. What is logged, where does it go, and what makes it hold up?
What is logged Significant actions only , defined explicitly rather than logging everything — an audit trail nobody can search is not usable evidence: Authentic
Design the network layout for a three-tier application in one cloud region. What are the decisions you cannot easily change later?
What the interviewer is testing Whether you know which network decisions are cheap and which are effectively permanent. This is a knowledge question with a clea
Design the timeout configuration for a request that passes through gateway, orders, pricing and inventory. What numbers, and what rule generates them?
The rule that generates the numbers One budget at the edge, decreasing inward, with room for a retry at exactly one layer. Start from what the caller will actua
Control Design vs Operation
A control that is well designed and never runs fails exactly like one that is absent.
Managed vs Self-Managed
Trading control and unit cost against operational attention.
Security vs Usability
Varying control by the value of the action rather than uniformly.
Strong vs Eventual Consistency
A per-operation decision, resolved by what a stale read would cost.
Analytics Cost Control
Scanned bytes, idle warehouses, and the query nobody knew was running hourly.
Backpressure & Flow Control
Telling callers to slow down instead of buffering into congestion collapse.
Build vs Buy
Differentiation versus table stakes, priced over five years.
Build vs Buy
Differentiation, five-year TCO, and the exit cost of each option.
CDC Pipeline Design
Building on a change stream: snapshot plus delta, tombstones, and merge into the target.
Centralised vs Distributed
Shared platform leverage against team autonomy.
Change Advisory vs Automated Gates
Replacing a weekly board with evidence a machine produces on every change.
Change Management vs CD
Reconciling CAB-era controls with continuous delivery without pretending either away.
Cost vs Reliability
Each nine costing an order of magnitude, and pricing the failure instead.
Delivery vs Maintainability
Fast in the cheap places, careful in the expensive ones.
Design Authority
How an ARB should decide, what it should not review, and how it avoids becoming a queue.
Design Patterns
Reusable solutions at code level, and when they become ceremony.
Design Systems
Components as a versioned internal product, with adoption and deprecation like any API.