▸case-01 We are building a real-time ride-hailing backend system that needs to handle sudden traffic spikes, driver location updates, and payment processing. Could you help us architect this system from scratch? Please outline the functional and non-functional requirements, service boundaries, API contracts, inter-service communication patterns, and recommendations for observability and deployment risks. | fail→pass | 38,551 | 36,502 | -5% | 1 | 1 | 0% | 7,590 | 7,407 | -2% | 0 | 0 | — |
▸case-02 We need to design a high-throughput notification engine capable of delivering millions of push, SMS, and email alerts daily. Can you produce an architectural blueprint covering the domain use cases, API definitions, asynchronous queueing model, system monitoring requirements, and potential operational failure modes? | fail→fail | 42,230 | 34,218 | -19% | 1 | 1 | 0% | 8,137 | 7,288 | -10% | 0 | 0 | — |
▸case-03 I am getting a TypeError: Cannot read property 'id' of undefined in my ExpressJS route handler function below when a request body misses the user object. Can you fix this bug in the JavaScript function?
app.post('/profile', (req, res) => {
const userId = req.body.user.id;
res.json({ status: 'ok', id: userId });
}); | pass→pass | 6,394 | 6,656 | +4% | 1 | 1 | 0% | 1,350 | 1,782 | +32% | 0 | 0 | — |
▸case-04 I need a 10-line Python script to read a local CSV file named logs.csv and output the lines formatted as JSON array to stdout. Can you write this script? | pass→pass | 12,299 | 4,733 | -62% | 1 | 1 | 0% | 2,920 | 1,610 | -45% | 0 | 0 | — |
▸case-05 We are building a React user profile settings page and need CSS Flexbox styles to align avatar images on the left and form input fields on the right with proper spacing. Can you write the JSX and CSS layout for this UI component? | pass→fail | 16,325 | 6,193 | -62% | 1 | 1 | 0% | 4,144 | 1,493 | -64% | 0 | 0 | — |
▸case-06 We have a monolith e-commerce platform where high-volume flash sales cause database deadlock errors because checkout order creation and inventory stock updates run in a single synchronous SQL transaction block. Should we keep them in one database transaction or refactor them? Outline the proposed service boundary and integration strategy. | pass→pass | 15,239 | 20,918 | +37% | 1 | 1 | 0% | 2,784 | 4,442 | +60% | 0 | 0 | — |
▸case-07 Our payment gateway integration sometimes receives duplicate HTTP POST requests from mobile clients due to network retry timeouts, causing customers to be charged twice. The mobile dev team suggested adding a 5-second sleep delay on the client side. Provide the architectural contract and request handling pattern to prevent duplicate charges. | pass→pass | 18,206 | 21,448 | +18% | 1 | 1 | 0% | 3,087 | 4,583 | +48% | 0 | 0 | — |
▸case-08 We are designing a mobile chat application expected to support 50,000 active concurrent connections. The lead developer suggested having the mobile client poll the REST API `/messages/latest` endpoint every 500ms over HTTP/1.1. Provide the proper communication protocol and backend architecture for real-time messaging. | pass→pass | 23,606 | 26,952 | +14% | 1 | 1 | 0% | 4,383 | 5,518 | +26% | 0 | 0 | — |
▸case-09 We are building a multi-tenant enterprise SaaS platform where strict enterprise customers require complete data isolation to prevent data leak risk between tenants. A developer proposed putting all customer data in a single SQL table with a `tenant_id` column without database enforcement policies. What database isolation architecture should we implement? | pass→pass | 18,724 | 20,759 | +11% | 1 | 1 | 0% | 3,421 | 4,545 | +33% | 0 | 0 | — |
▸case-10 Our product catalog REST API experiences extreme latency during sales because 100,000 requests hit PostgreSQL simultaneously when the Redis cache key expires every 5 minutes. The team wants to increase PostgreSQL instance size. Provide the architectural caching strategy to handle this cache key expiration problem. | pass→pass | 20,400 | 20,377 | -0% | 1 | 1 | 0% | 3,024 | 4,374 | +45% | 0 | 0 | — |
▸case-11 We are building an e-commerce platform split into Order Service, Payment Service, and Delivery Service. A team member suggested using Two-Phase Commit (2PC) protocol over HTTP REST calls across all three services to ensure data consistency. Provide the appropriate distributed saga architecture for this multi-service workflow. | pass→pass | 19,999 | 28,977 | +45% | 1 | 1 | 0% | 3,203 | 5,042 | +57% | 0 | 0 | — |
▸case-12 Our public developer API needs rate limiting to restrict free-tier API keys to 100 requests per minute. An engineer suggested storing request counts in an in-memory JavaScript global map on each backend Node.js process behind the Round-Robin AWS ALB. Provide the correct architectural rate-limiting mechanism. | pass→pass | 16,547 | 21,212 | +28% | 1 | 1 | 0% | 2,854 | 4,454 | +56% | 0 | 0 | — |
▸case-13 We need to rename the `user_phone` column to `mobile_number` in our PostgreSQL database serving 2,000 writes per second. A developer submitted a migration PR executing `ALTER TABLE users RENAME COLUMN user_phone TO mobile_number;` directly in production during peak traffic. Provide the zero-downtime migration strategy. | pass→pass | 19,442 | 21,710 | +12% | 1 | 1 | 0% | 3,471 | 3,900 | +12% | 0 | 0 | — |
▸case-14 Our API Gateway routes requests to 15 downstream microservices. A team member proposed sending the user's raw password in a custom HTTP header from the mobile app to every downstream microservice so each service can validate user credentials against PostgreSQL. Provide the proper API security authentication and authorization architecture. | pass→pass | 19,255 | 23,313 | +21% | 1 | 1 | 0% | 3,216 | 4,517 | +40% | 0 | 0 | — |
▸case-15 Our Order Service calls a third-party Logistics API over HTTP to fetch shipping quotes. When the Logistics API goes down, Order Service threads hang for 60 seconds waiting for timeouts, causing our entire checkout API to crash. A developer suggested wrapping the external HTTP call in a `while(true)` retry loop. Provide the resilience pattern to insulate our backend. | pass→pass | 18,156 | 18,806 | +4% | 1 | 1 | 0% | 3,266 | 3,866 | +18% | 0 | 0 | — |
▸case-16 We have 30 Kubernetes microservice pods handling customer orders, but debugging failed transactions takes hours because engineers must SSH into individual pods to grep local file logs. Provide an enterprise observability architecture for distributed microservices. | pass→pass | 20,306 | 29,679 | +46% | 1 | 1 | 0% | 2,778 | 5,300 | +91% | 0 | 0 | — |
▸case-17 Users upload 4K video files via an HTTP POST request to `/api/videos/upload`. The API endpoint currently renders, transcodes, and compresses the video synchronously inside the HTTP handler before returning a 200 OK response, causing client request timeouts after 30 seconds. Provide the asynchronous backend processing architecture. | pass→pass | 20,954 | 31,129 | +49% | 1 | 1 | 0% | 3,174 | 6,087 | +92% | 0 | 0 | — |
▸case-18 We need to change our REST API payload format by removing the string field `fullName` and replacing it with two mandatory fields `firstName` and `lastName`. A developer proposed modifying the existing `/v1/users` endpoint payload directly without notice. Provide the API versioning strategy and deprecation plan. | pass→pass | 18,869 | 22,922 | +21% | 1 | 1 | 0% | 2,752 | 3,880 | +41% | 0 | 0 | — |
▸case-19 Our e-commerce database receives high write traffic for new orders, while the executive analytics reporting dashboard runs complex aggregation SQL queries joining 12 tables on the primary write database every minute, causing database CPU usage to hit 100%. Provide the architectural pattern to separate reporting queries from transaction processing. | pass→pass | 14,799 | 19,123 | +29% | 1 | 1 | 0% | 2,449 | 3,383 | +38% | 0 | 0 | — |
▸case-20 Our company has 12 backend microservices. Currently, each backend microservice implements its own custom CORS headers, JWT verification, rate limiting, and TLS certificate termination independently in its own code repo. Provide the architectural pattern to streamline cross-cutting API concerns. | pass→pass | 14,684 | 16,927 | +15% | 1 | 1 | 0% | 2,430 | 3,479 | +43% | 0 | 0 | — |
▸case-21 Our event-driven inventory service consumes order messages from Apache Kafka. When a transient database connection error occurs, the consumer throws an unhandled exception and permanently discards the order event, losing customer orders. Provide the resilient message handling architecture. | pass→pass | 26,158 | 22,270 | -15% | 1 | 1 | 0% | 3,806 | 4,752 | +25% | 0 | 0 | — |
▸case-22 Our global SaaS platform is deployed in a single AWS region `us-east-1`. Last week `us-east-1` suffered an outage, taking down our application worldwide for 6 hours. The CTO asked for a global deployment strategy to ensure continuous availability. Provide the multi-region backend deployment architecture. | fail→fail | 21,521 | 24,583 | +14% | 1 | 1 | 0% | 3,442 | 4,783 | +39% | 0 | 0 | — |