scenario: Debugging a memory leak in a Node.js application

thought_process: 1. Observed memory usage increasing over time despite garbage collection. 2. Checked heap snapshots and noticed growing arrays. 3. Traced back to event listeners not being removed. 4. Identified that EventEmitter listeners were accumulating on shared objects. 5. Realized the root cause was missing cleanup in component lifecycle methods.

decision: Implement proper cleanup in component unmount methods to remove all event listeners using .off() or .removeListener(). Add memory leak detection tests to prevent recurrence.

rejected_approaches: Increasing heap size: rejected as this only delays the problem, doesn't fix it. Manual garbage collection: rejected as it's not guaranteed to collect all unreferenced objects and is a bad practice.


scenario: Choosing between REST vs GraphQL for a new API

thought_process: 1. Analyzed client requirements: mobile app needs flexible data fetching. 2. Considered team expertise: team has strong REST experience, limited GraphQL knowledge. 3. Evaluated data complexity: moderately complex nested relationships. 4. Considered caching needs: CDN caching important for performance. 5. Weighed development overhead: GraphQL requires more setup and tooling.

decision: Start with REST API for simplicity and better caching support. Consider GraphQL wrapper in the future if client needs become more complex.

rejected_approaches: Pure GraphQL: rejected due to team learning curve and caching complexity. Pure REST with over-fetching: rejected as it would lead to inefficient mobile data usage.


scenario: Database index selection for slow queries

thought_process: 1. Analyzed slow query logs identifying queries taking >500ms. 2. Examined EXPLAIN output showing full table scans. 3. Reviewed WHERE and JOIN clauses to understand filter patterns. 4. Considered selectivity of columns (high cardinality = good index candidate). 5. Evaluated write vs read ratio (90% reads, 10% writes). 6. Calculated index maintenance cost vs query performance gain.

decision: Add composite indexes on (user_id, created_at) for user dashboard queries. Add separate index on status for filtering. Monitor query performance after deployment.

rejected_approaches: Indexing all columns: rejected due to excessive write overhead and storage. No indexes: rejected as queries are already causing user-facing delays.


scenario: Refactoring a monolithic function

thought_process: 1. Identified a 400-line function handling multiple responsibilities. 2. Examined function complexity and dependencies between logic blocks. 3. Considered extracting smaller functions but worried about state management. 4. Evaluated creating a class to encapsulate related operations. 5. Assessed test coverage for the existing function. 6. Determined the risk of introducing bugs during refactoring.

decision: Refactor into a class with private methods for each logical unit. Write comprehensive tests for the new structure before refactoring. Use feature flags to roll back if issues arise.

rejected_approaches: Leaving as-is: rejected as technical debt is making future changes difficult. Complete rewrite: rejected as too risky without fully understanding all edge cases.


scenario: Choosing a frontend framework for a new project

thought_process: 1. Analyzed project requirements: real-time updates, complex state management. 2. Considered team experience: React expertise available, no Vue experience. 3. Evaluated ecosystem: React has mature libraries for real-time features. 4. Assessed hiring needs: React developers are more available in the market. 5. Considered long-term maintenance: large community and corporate backing for React.

decision: Choose React with TypeScript for type safety and better developer experience. Use React Query for server state and Zustand for client state management.

rejected_approaches: Vue.js: rejected due to lack of team experience and smaller ecosystem. Angular: rejected as too opinionated and heavy for the project needs. Vanilla JS: rejected as it would require building state management from scratch.


scenario: Handling API rate limiting for third-party service

thought_process: 1. Observed 429 Too Many Requests errors from external API. 2. Reviewed rate limit documentation: 100 requests per minute. 3. Analyzed current usage patterns: bursts of requests during peak hours. 4. Considered implementing exponential backoff. 5. Evaluated request queuing vs caching strategies. 6. Assessed the cost of upgraded API tier vs implementation complexity.

decision: Implement request throttling with a token bucket algorithm. Add response caching for idempotent GET requests. Queue non-critical writes during off-peak hours.

rejected_approaches: Ignoring rate limits: rejected as it would cause service disruption. Paying for higher tier immediately: rejected as we should optimize usage first. Simple delay: rejected as it doesn't adapt to varying rate limits.


scenario: Database migration strategy for large table

thought_process: 1. Need to add column to 100M row table with minimal downtime. 2. Considered ALTER TABLE directly but estimated 2+ hours of locking. 3. Evaluated online schema change tools like pt-online-schema-change. 4. Thought about creating new table and syncing data. 5. Assessed application compatibility during migration. 6. Calculated storage requirements for duplicate tables.

decision: Use a three-phase migration: 1) Add new nullable column without default value, 2) Backfill data in batches, 3) Make column NOT NULL with default. Use application-level reads from both old and new columns during transition.

rejected_approaches: Direct ALTER TABLE: rejected due to unacceptable table locking. Recreation of table: rejected as too complex and risky for this change.


scenario: Code review: security vulnerability in authentication

thought_process: 1. Noticed JWT tokens stored in localStorage during code review. 2. Considered XSS attack vector: any malicious script can access localStorage. 3. Evaluated alternatives: httpOnly cookies, session-based auth. 4. Assessed UX implications: cookies need CSRF protection. 5. Considered existing architecture and migration effort.

decision: Migrate from localStorage to httpOnly, secure, sameSite cookies for JWT storage. Implement CSRF token validation for all state-changing operations. Add Content-Security-Policy headers.

rejected_approaches: Keeping current approach: rejected as it's a significant security vulnerability. In-memory storage: rejected as tokens would be lost on refresh.


scenario: Performance optimization: slow page load times

thought_process: 1. Measured LCP (Largest Contentful Paint) at 4.5 seconds, above target of 2.5s. 2. Analyzed waterfall chart showing late JavaScript bundles loading. 3. Identified large vendor bundle (1.2MB) blocking rendering. 4. Considered code splitting strategies. 5. Evaluated lazy loading vs eager loading for above-the-fold content. 6. Assessed impact on user experience and SEO.

decision: Implement route-based code splitting using React.lazy(). Defer non-critical JavaScript using script defer attribute. Preload critical CSS and fonts. Prioritize above-the-fold content rendering.

rejected_approaches: Minification only: rejected as insufficient for the performance gap. Server-side rendering: rejected as too complex for current infrastructure and requirements.


scenario: API versioning strategy

thought_process: 1. Need to introduce breaking changes to existing API endpoints. 2. Considered URL path versioning (/v1/, /v2/). 3. Evaluated header-based versioning (Accept: application/vnd.api+json; version=2). 4. Assessed client migration effort and compatibility. 5. Thought about backward compatibility requirements. 6. Considered deprecation timeline for old versions.

decision: Use URL path versioning for clarity and ease of use. Maintain v1 for 6 months with deprecation warnings. Document migration guide for clients. Sunset old versions after notification period.

rejected_approaches: No versioning: rejected as breaking changes would disrupt existing clients. Header versioning: rejected as less discoverable and harder to test manually.


scenario: Error handling strategy for microservices

thought_process: 1. Observed cascading failures when one service goes down. 2. Analyzed failure modes: timeout, connection refused, 500 errors. 3. Considered circuit breaker pattern to prevent cascading failures. 4. Evaluated retry strategies with exponential backoff. 5. Assessed fallback mechanisms and degraded functionality. 6. Thought about monitoring and alerting requirements.

decision: Implement circuit breaker using Hystrix or Resilience4j. Add retries with exponential backoff for idempotent operations. Provide cached fallback data when services are unavailable. Implement comprehensive health checks.

rejected_approaches: No error handling: rejected as it causes system-wide failures. Always retry: rejected as it can overwhelm struggling services (thundering herd problem).


scenario: Testing strategy for legacy code

thought_process: 1. Need to modify critical legacy code with no tests. 2. Considered writing tests before changes (TDD approach). 3. Evaluated characterization tests to capture current behavior. 4. Assessed risk of introducing bugs during refactoring. 5. Thought about time constraints vs code quality. 6. Considered incremental refactoring approach.

decision: Write characterization tests first to document current behavior. Extract the specific code section to be modified into a testable unit. Write focused tests for the new logic. Run both old and new tests in parallel during transition.

rejected_approaches: Modify without tests: rejected as too risky for critical legacy code. Full rewrite: rejected as time-prohibitive and risky without full understanding.


scenario: Caching strategy for content delivery

thought_process: 1. Analyzed content patterns: static assets, user-specific data, real-time updates. 2. Considered CDN caching for static content. 3. Evaluated edge caching vs origin caching. 4. Assessed cache invalidation challenges for dynamic content. 5. Thought about cache stampede prevention for popular content. 6. Calculated cache hit ratio targets and cost savings.

decision: Implement multi-layer caching: CDN for static assets with long TTL, Redis for dynamic content with 5-minute TTL, application-level cache for computed results. Use cache warming for frequently accessed content. Implement cache invalidation webhooks.

rejected_approaches: No caching: rejected as it puts unnecessary load on servers. Single cache layer: rejected as it doesn't optimize for different content types and access patterns.


scenario: Database sharding decision

thought_process: 1. Database at 500GB with performance degradation. 2. Analyzed query patterns and data access frequency. 3. Considered horizontal vs vertical scaling options. 4. Evaluated sharding keys based on user geography or data type. 5. Assessed cross-shard query complexity. 6. Thought about application changes required.

decision: Implement horizontal sharding by customer_id for even distribution. Use consistent hashing to minimize re-sharding. Maintain a lookup table for shard location. Implement application-level routing to avoid cross-shard joins.

rejected_approaches: Vertical scaling: rejected as too expensive and has limits. Read replicas: rejected as write performance is the bottleneck, not reads.


scenario: Secrets management approach

thought_process: 1. Found hardcoded secrets in repository. 2. Considered environment variables approach. 3. Evaluated dedicated secrets management solutions (HashiCorp Vault, AWS Secrets Manager). 4. Assessed rotation requirements and audit needs. 5. Thought about developer experience and access control. 6. Considered compliance requirements (SOC2, GDPR).

decision: Migrate to AWS Secrets Manager for cloud-hosted applications. Use environment variables injected from secrets manager at runtime. Implement automatic secret rotation. Restrict access using IAM roles. Add secrets scanning to CI/CD pipeline.

rejected_approaches: Continue with hardcoded secrets: rejected as major security violation. Simple .env files: rejected as secrets can be accidentally committed and lack audit trail.


scenario: Logging strategy for distributed systems

thought_process: 1. Difficulty debugging requests across multiple services. 2. Considered correlation ID propagation. 3. Evaluated structured logging vs plain text. 4. Assessed log aggregation solutions (ELK, CloudWatch, Splunk). 5. Thought about log retention costs and search performance. 6. Considered sensitive data redaction requirements.

decision: Implement structured JSON logging with correlation IDs. Use OpenTelemetry for distributed tracing. Aggregate logs in Elasticsearch with 30-day retention. Redact PII and sensitive data before indexing. Set up alerts for error patterns.

rejected_approaches: Plain text logs: rejected as difficult to parse and query. No correlation: rejected as impossible to trace requests across services.


scenario: Feature flag implementation

thought_process: 1. Need to release feature gradually to monitor for issues. 2. Considered simple config file approach. 3. Evaluated feature flag management services (LaunchDarkly, Split.io). 4. Assessed rollback speed and safety requirements. 5. Thought about A/B testing needs. 6. Considered user segmentation capabilities.

decision: Implement a simple feature flag system using Redis with admin UI. Gradually roll out to 1%, 5%, 10%, 50%, 100% of users. Monitor metrics at each stage. Include kill switch for instant rollback.

rejected_approaches: Full release without flags: rejected as too risky for critical feature. Full-featured third-party service: rejected as overkill for current needs and adds dependency.


scenario: SQL vs NoSQL database selection

thought_process: 1. Analyzing data structure: hierarchical document with varying schemas. 2. Considered ACID requirements: strong consistency needed for transactions. 3. Evaluated query patterns: mostly document retrieval, some joins needed. 4. Assessed scaling requirements: need to handle 10x growth. 5. Thought about development velocity and team expertise. 6. Considered eventual consistency trade-offs.

decision: Choose PostgreSQL with JSONB support for the best of both worlds: ACID compliance with flexible schema support. Use JSONB for document storage and relational features for structured data when needed.

rejected_approaches: Pure MongoDB: rejected due to ACID requirements for transactions. Pure relational: rejected as it would require complex schema migrations for varying document structures.


scenario: Mobile app offline-first architecture

thought_process: 1. Need to support intermittent connectivity for field workers. 2. Considered local SQLite database with sync. 3. Evaluated conflict resolution strategies (last-write-wins, operational transformation). 4. Assessed storage constraints on mobile devices. 5. Thought about data consistency requirements. 6. Considered user experience during sync conflicts.

decision: Implement SQLite local storage with incremental sync. Use last-write-wins with timestamps for conflict resolution. Queue operations when offline, sync when connected. Show sync status and conflict resolution UI to users.

rejected_approaches: Online-only: rejected as field workers need offline access. Manual sync: rejected as too error-prone and poor user experience.


scenario: WebSocket vs Server-Sent Events for real-time updates

thought_process: 1. Need real-time updates from server to client. 2. Considered bidirectional communication needs. 3. Evaluated connection overhead and scalability. 4. Assessed browser compatibility requirements. 5. Thought about fallback for older browsers. 6. Considered infrastructure complexity.

decision: Use Server-Sent Events for server-to-client updates (simpler, auto-reconnect). Use REST API for client-to-server communication. Add WebSocket only if bidirectional real-time becomes necessary.

rejected_approaches: WebSocket for everything: rejected as overkill for unidirectional updates. Polling: rejected as inefficient and poor user experience.


scenario: CI/CD pipeline design

thought_process: 1. Need to automate testing and deployment process. 2. Considered container-based vs VM-based builds. 3. Evaluated pipeline stages: lint, test, build, deploy. 4. Assessed parallel execution opportunities. 5. Thought about rollback mechanisms. 6. Considered security scanning requirements.

decision: Implement multi-stage pipeline: parallel lint and unit tests, then build, then integration tests, then staged deployment (dev -> staging -> production). Use container caching for faster builds. Include security and dependency scans.

rejected_approaches: Single long-running pipeline: rejected as too slow. Skipping tests for speed: rejected as it allows bugs to reach production.


scenario: Rate limiting algorithm selection

thought_process: 1. Need to protect API from abuse while allowing legitimate use. 2. Considered fixed window counter approach. 3. Evaluated sliding window log for accuracy. 4. Assessed token bucket for burst handling. 5. Thought about distributed implementation complexity. 6. Considered memory requirements for each algorithm.

decision: Implement token bucket algorithm using Redis for distributed tracking. Allow short bursts within limits while maintaining sustained rate limits. Use different limits for authenticated vs anonymous users.

rejected_approaches: Fixed window: rejected as allows double requests at window boundaries. No rate limiting: rejected as system vulnerable to abuse and DoS attacks.


scenario: Event-driven architecture adoption

thought_process: 1. Multiple services need to react to user actions. 2. Considered direct HTTP calls between services. 3. Evaluated message broker options (Kafka, RabbitMQ, AWS SQS). 4. Assessed ordering and delivery guarantees needed. 5. Thought about eventual consistency implications. 6. Considered operational complexity.

decision: Implement event-driven architecture using AWS SNS/SQS. Use pub/sub for notifications and queues for async processing. Start with critical events and expand gradually. Add dead letter queues for failed messages.

rejected_approaches: Synchronous HTTP: rejected as creates tight coupling and cascading failures. Full microservices with Kafka: rejected as too complex for current scale and team size.


scenario: Type safety in JavaScript project

thought_process: 1. Experiencing runtime type errors in production. 2. Considered adding PropTypes for React components. 3. Evaluated TypeScript migration effort. 4. Assessed team learning curve and productivity impact. 5. Thought about incremental migration strategy. 6. Considered build tool and ecosystem compatibility.

decision: Migrate to TypeScript incrementally using allowJS setting. Start with new files and high-risk modules. Use any types temporarily for legacy code. Enable strict mode gradually as team gains experience.

rejected_approaches: JSDoc type checking: rejected as less comprehensive than TypeScript. PropTypes only: rejected as runtime-only and doesn't catch all type errors.


scenario: Database backup strategy

thought_process: 1. Need to ensure data durability and recovery capability. 2. Considered full daily backups with transaction logs. 3. Evaluated point-in-time recovery requirements. 4. Assessed RPO (Recovery Point Objective) and RTO (Recovery Time Objective). 5. Thought about cross-region redundancy for disaster recovery. 6. Calculated storage costs and retention policy.

decision: Implement continuous backup with point-in-time recovery to 35 days. Use automated daily snapshots with 30-day retention. Store backups in separate region for disaster recovery. Test restore process monthly.

rejected_approaches: Manual backups: rejected as unreliable and error-prone. Single daily backup: rejected as too much data loss potential (24 hours).


scenario: API authentication method

thought_process: 1. Need to secure API endpoints for external partners. 2. Considered API key authentication. 3. Evaluated OAuth 2.0 with client credentials flow. 4. Assessed security requirements and user context needs. 5. Thought about revocation and rotation capabilities. 6. Considered implementation complexity vs security benefit.

decision: Implement OAuth 2.0 client credentials flow for machine-to-machine communication. Use short-lived access tokens (15 minutes) with refresh mechanism. Provide API keys as fallback for simple integrations.

rejected_approaches: Basic authentication: rejected as insecure and lacks granular control. No authentication: rejected as data would be publicly accessible.


scenario: Microservice boundary definition

thought_process: 1. Monolithic application becoming difficult to maintain. 2. Considered splitting by technical layers (database, API, UI). 3. Evaluated domain-driven design bounded contexts. 4. Assessed data consistency requirements across boundaries. 5. Thought about deployment independence needs. 6. Considered team organizational structure.

decision: Split by business domain following DDD principles. Start with user management and order processing as separate services. Define clear APIs between services. Accept eventual consistency where appropriate.

rejected_approaches: Split by technical layer: rejected as creates distributed monolith with all the complexity and no benefit. Database per service immediately: rejected as premature optimization without clear boundaries.


scenario: Search functionality implementation

thought_process: 1. Need to implement product search for e-commerce site. 2. Considered SQL LIKE queries for simplicity. 3. Evaluated dedicated search solutions (Elasticsearch, Algolia, Typesense). 4. Assessed search requirements: fuzzy matching, faceting, ranking. 5. Thought about indexing strategy and update frequency. 6. Calculated infrastructure costs.

decision: Implement Elasticsearch for search functionality. Use inverted index for fast full-text search. Add autocomplete and typo tolerance. Reindex products on update. Use application-level caching for popular searches.

rejected_approaches: SQL LIKE: rejected as doesn't scale and lacks search features. Google Custom Search: rejected as limited customization and control.


scenario: Image optimization strategy

thought_process: 1. Images causing slow page loads and high bandwidth costs. 2. Considered manual optimization workflow. 3. Evaluated automated CDN solutions (Cloudinary, imgix). 4. Assessed format options: WebP, AVIF, fallback to JPEG. 5. Thought about responsive image needs for different devices. 6. Calculated cost savings vs CDN costs.

decision: Implement responsive images with WebP/AVIF support using Sharp for optimization. Use srcset for device-appropriate serving. Configure CDN caching headers. Lazy load images below the fold.

rejected_approaches: Manual optimization: rejected as unsustainable at scale. Single image size: rejected as wastes bandwidth on mobile and poor quality on desktop.


thought_process: 1. Planning expansion to European markets. 2. Considered text extraction and translation workflow. 3. Evaluated i18n libraries (react-i18next, vue-i18n). 4. Assessed requirements beyond text: dates, currencies, numbers, RTL languages. 5. Thought about content management for translations. 6. Considered SEO implications for multilingual content.

decision: Implement i18next with namespace organization. Extract all text to translation files. Use ICU message syntax for complex messages. Format dates, numbers, and currencies by locale. Add hreflang tags for SEO.

rejected_approaches: Duplicate codebase per language: rejected as maintenance nightmare. Machine translation only: rejected as quality issues and cultural nuances missed.


scenario: Dependency injection approach

thought_process: 1. Code has tight coupling making testing difficult. 2. Considered constructor injection pattern. 3. Evaluated framework DI solutions (InversifyJS, Awilix). 4. Assessed impact on code readability and simplicity. 5. Thought about circular dependency issues. 6. Considered learning curve for team.

decision: Use manual constructor injection with TypeScript for type safety. Keep it simple without framework overhead. Use factory functions for complex object graphs. Add tests that can inject mock dependencies easily.

rejected_approaches: Service locator pattern: rejected as hides dependencies. No DI (instantiating dependencies directly): rejected as makes testing impossible and creates tight coupling.


scenario: Data migration from legacy system

thought_process: 1. Need to migrate 5 years of customer data to new system. 2. Considered big-bang cutover approach. 3. Evaluated phased migration with parallel running. 4. Assessed data validation requirements. 5. Thought about rollback plan if issues arise. 6. Considered downtime tolerance for business.

decision: Implement phased migration with dual-write strategy. Write to both systems during transition. Migrate historical data in batches. Validate data integrity at each step. Keep legacy system in read-only mode for 30 days.

rejected_approaches: Big-bang cutover: rejected as too risky with no rollback path. Manual data entry: rejected as error-prone and time-consuming.


scenario: Monitoring and alerting strategy

thought_process: 1. Currently discovering issues from users, not proactive. 2. Considered simple health checks. 3. Evaluated comprehensive monitoring (Prometheus, DataDog, New Relic). 4. Assessed key metrics: RED method (Rate, Errors, Duration) and USE method (Utilization, Saturation, Errors). 5. Thought about alert fatigue prevention. 6. Considered integration with incident response.

decision: Implement the Four Golden Signals monitoring: latency, traffic, errors, saturation. Use Prometheus for metrics collection. Set up alert thresholds based on SLOs. Create runbooks for common incidents. Integrate with PagerDuty for on-call.

rejected_approaches: User reports only: rejected as reactive and poor customer experience. Over-monitoring: rejected as creates noise and alert fatigue.


scenario: State management for React application

thought_process: 1. Managing complex application state with useState only. 2. Considered Context API for global state. 3. Evaluated specialized state libraries (Redux, Zustand, Jotai). 4. Assessed state complexity: mostly server state with some client UI state. 5. Thought about developer experience and boilerplate. 6. Considered bundle size impact.

decision: Use React Query for server state management (caching, invalidation, refetching). Use Zustand for minimal client UI state. Avoid Context for frequently changing state to prevent re-renders.

rejected_approaches: Redux: rejected as overkill and too much boilerplate. Everything in Context: rejected as performance issues with frequent updates.


scenario: Email delivery strategy

thought_process: 1. Transactional emails frequently landing in spam. 2. Considered configuring own mail server. 3. Evaluated email service providers (SendGrid, AWS SES, Mailgun). 4. Assessed deliverability requirements and tracking needs. 5. Thought about volume and cost scaling. 6. Considered template management and personalization.

decision: Migrate to AWS SES with dedicated IP for better deliverability. Implement SPF, DKIM, and DMARC records. Use CloudWatch for delivery metrics. Create email templates in separate service for easy updates.

rejected_approaches: Own mail server: rejected as difficult to maintain and poor deliverability. Gmail/Outlook SMTP: rejected as violates terms of service and limits.


scenario: File upload handling

thought_process: 1. Users uploading large files causing timeouts. 2. Considered direct multipart upload to S3. 3. Evaluated resumable upload libraries (tus.io). 4. Assessed security concerns: file type validation, size limits. 5. Thought about processing workflow after upload (virus scan, thumbnails). 6. Considered user experience during upload.

decision: Implement client-side direct upload to S3 with presigned URLs. Add chunked upload for files >100MB. Validate file types on both client and server. Process files asynchronously after upload.

rejected_approaches: Proxy through server: rejected as causes timeout and memory issues. No validation: rejected as security vulnerability.


scenario: SEO optimization for SPA

thought_process: 1. React SPA not indexing well in search engines. 2. Considered pre-rendering with static site generation. 3. Evaluated server-side rendering (Next.js). 4. Assessed dynamic content requirements vs static content. 5. Thought about maintenance overhead and deployment complexity. 6. Considered incremental static regeneration option.

decision: Migrate to Next.js with hybrid approach: static generation for marketing pages, SSR for dynamic content, client-side for authenticated areas. Implement proper meta tags and structured data.

rejected_approaches: Prerender.io: rejected as expensive and doesn't handle dynamic content. Stay as SPA: rejected as poor SEO and social sharing.


scenario: A/B testing implementation

thought_process: 1. Need to test new feature before full rollout. 2. Considered simple feature flag approach. 3. Evaluated A/B testing platforms (Optimizely, Google Optimize). 4. Assessed statistical significance requirements. 5. Thought about tracking and analytics integration. 6. Considered multiple variant testing needs.

decision: Build simple A/B testing framework with consistent hashing. Track events in analytics platform. Calculate statistical significance before making decisions. Document results for future reference.

rejected_approaches: Full rollout without testing: rejected as risky for user-facing changes. Expensive platform: rejected as overkill for current testing needs.


scenario: Database transaction isolation level

thought_process: 1. Experiencing deadlocks in high-concurrency scenarios. 2. Analyzed current isolation level (SERIALIZABLE). 3. Evaluated lower isolation levels (READ COMMITTED, REPEATABLE READ). 4. Assessed consistency requirements for business logic. 5. Thought about phantom read and dirty read risks. 6. Considered performance vs correctness trade-off.

decision: Lower isolation to READ COMMITTED with row-level locks where needed. Use SELECT FOR UPDATE for critical sections. Implement optimistic concurrency control with version numbers where appropriate.

rejected_approaches: Stay at SERIALIZABLE: rejected as causes excessive deadlocks and poor performance. No transactions: rejected as risks data inconsistency.


scenario: Webhook delivery reliability

thought_process: 1. Webhooks occasionally failing to reach clients. 2. Considered simple retry with exponential backoff. 3. Evaluated queue-based delivery with DLQ. 4. Assessed idempotency requirements for duplicate deliveries. 5. Thought about signature verification for security. 6. Considered client notification preferences.

decision: Implement webhook delivery with message queue (RabbitMQ/SQS). Retry with exponential backoff up to 3 days. Use HMAC signatures for verification. Provide webhook status dashboard and retry capability to clients.

rejected_approaches: Fire and forget: rejected as unreliable. Synchronous delivery: rejected as blocks main request processing.


scenario: Color scheme selection for accessibility

thought_process: 1. Designing UI for diverse user base including colorblind users. 2. Considered WCAG contrast ratio requirements (4.5:1 for normal text). 3. Evaluated color blindness simulators to test palettes. 4. Assessed not just color but also patterns/icons for information. 5. Thought about dark mode support. 6. Considered user testing with accessibility tools.

decision: Design with WCAG AA compliance as baseline. Use high contrast colors (7:1 for preference). Support both light and dark themes. Never rely on color alone to convey information. Test with axe DevTools and real users.

rejected_approaches: Aesthetic over accessibility: rejected as excludes users with disabilities. Single theme: rejected as doesn't support user preferences and environmental conditions.


scenario: API documentation strategy

thought_process: 1. API documentation is scattered and outdated. 2. Considered Swagger/OpenAPI specification. 3. Evaluated auto-generation from code annotations. 4. Assessed developer experience needs (try it out, examples). 5. Thought about documentation maintenance workflow. 6. Considered client SDK generation.

decision: Implement OpenAPI 3.0 specification with Swagger UI. Auto-generate from code annotations where possible. Include code examples in multiple languages. Generate client SDKs for popular languages. Keep docs in sync with API versioning.

rejected_approaches: Wiki/Confluence: rejected as disconnected from code and hard to maintain. No documentation: rejected as poor developer experience and adoption.


scenario: Session storage backend selection

thought_process: 1. Using in-memory sessions, losing them on restart. 2. Considered database-backed sessions. 3. Evaluated Redis for session storage. 4. Assessed session size and frequency of access. 5. Thought about session expiration and cleanup. 6. Considered distributed application requirements.

decision: Migrate to Redis for session storage with TTL for automatic expiration. Use connection pooling for performance. Implement session compression for large sessions. Consider sticky sessions as fallback.

rejected_approaches: In-memory: rejected as lost on deploy and doesn't scale. Database: rejected as adds load to primary database and slower access.


scenario: Code ownership and review policy

thought_process: 1. No clear code ownership leading to review delays. 2. Considered strict owner approval requirement. 3. Evaluated tiered review requirements based on change risk. 4. Assessed team velocity vs quality needs. 5. Thought about knowledge sharing goals. 6. Considered on-call implications.

decision: Implement CODEOWNERS file with module ownership. Require approval for files in owned modules. Allow auto-approval for trivial changes (typo, formatting). Encourage pair programming for knowledge sharing.

rejected_approaches: Anyone can review: rejected as lacks accountability and expertise. Single approver bottleneck: rejected as slows down development unnecessarily.


scenario: Mobile app build and distribution

thought_process: 1. Manual build process is error-prone and slow. 2. Considered automating with Fastlane. 3. Evaluated CI/CD integration (Bitrise, App Center). 4. Assessed distribution needs (TestFlight, Play Store internal). 5. Thought about code signing and certificate management. 6. Considered beta testing workflow.

decision: Automate builds with GitHub Actions using Fastlane. Automatically distribute to TestFlight and Play Store internal track on merge to main. Store certificates securely in GitHub Secrets (encrypted). Use semantic versioning for releases.

rejected_approaches: Manual builds: rejected as error-prone and time-consuming. Local builds: rejected as not reproducible and lacks audit trail.


scenario: Error tracking and debugging

thought_process: 1. Only learning about production errors from users. 2. Considered simple logging to files. 3. Evaluated error tracking services (Sentry, Rollbar, Bugsnag). 4. Assessed need for stack traces, breadcrumbs, user context. 5. Thought about alerting on error rate spikes. 6. Considered performance monitoring correlation.

decision: Integrate Sentry for error tracking with source maps. Capture user context and breadcrumbs for debugging. Set up alerts for error rate increases. Correlate errors with performance data.

rejected_approaches: Email alerts: rejected as lacks context and actionable information. Log aggregation only: rejected as difficult to correlate errors into meaningful events.


scenario: Cost optimization for cloud infrastructure

thought_process: 1. Cloud costs increasing 50% quarter over quarter. 2. Analyzed usage patterns: development environments running 24/7. 3. Considered reserved instances for production workloads. 4. Evaluated auto-scaling policies for variable load. 5. Assessed idle resource elimination. 6. Thought about right-sizing resources.

decision: Implement schedule-based auto-shutdown for non-production environments. Use reserved instances for baseline production load. Add auto-scaling for variable workloads. Right-size instances based on actual metrics. Set up budget alerts.

rejected_approaches: Blind cost cutting: rejected as risks performance and availability. Ignore and pay: rejected as unsustainable and inefficient.


scenario: Database query optimization

thought_process: 1. Specific report query taking 45 seconds to run. 2. Analyzed execution plan showing multiple table scans. 3. Identified missing indexes on join columns. 4. Considered query restructuring to reduce joins. 5. Evaluated materialized view for pre-aggregation. 6. Assessed report freshness requirements.

decision: Add composite indexes for frequently joined columns. Restructure query to avoid N+1 pattern. Create materialized view refreshed hourly for historical reports. Add query result caching for repeated identical queries.

rejected_approaches: Denormalize tables: rejected as risks data inconsistency. Increase hardware: rejected as expensive and doesn't fix inefficient query.


scenario: Git workflow selection

thought_process: 1. Team struggling with merge conflicts and lost work. 2. Considered simple trunk-based development. 3. Evaluated GitFlow with feature branches. 4. Assessed deployment frequency and team size. 5. Thought about CI/CD integration. 6. Considered code review requirements.

decision: Implement simplified GitHub flow: feature branches to main, protected main branch requiring PRs and checks. Use draft PRs for early feedback. Delete branches after merge. Use rebase for clean history.

rejected_approaches: GitFlow: rejected as too complex for continuous deployment. No branching: rejected as makes code review difficult and risky.


scenario: Data privacy and GDPR compliance

thought_process: 1. Need to comply with GDPR for EU customers. 2. Considered data mapping and classification. 3. Evaluated consent management platforms. 4. Assessed right to be forgotten implementation. 5. Thought about data retention policies. 6. Considered data portability requirements.

decision: Implement data classification and inventory. Add consent management for data collection. Create GDPR-compliant delete endpoint that removes all personal data. Implement data export functionality. Document data processing activities.

rejected_approaches: Ignore GDPR: rejected as legal risk and fines. Geo-blocking EU: rejected as loses significant market opportunity.


scenario: API response format design

thought_process: 1. Inconsistent response formats across endpoints. 2. Considered simple envelope format. 3. Evaluated JSON:API specification for standardization. 4. Assessed client library needs and ease of use. 5. Thought about pagination, filtering, sorting. 6. Considered error response structure.

decision: Design consistent response format with success/error envelopes. Include standardized pagination, filtering, and sorting. Use appropriate HTTP status codes. Document all response formats with examples.

rejected_approaches: Different format per endpoint: rejected as confusing for clients. Over-engineered envelope: rejected as adds unnecessary complexity and parsing overhead.


scenario: Background job processing

thought_process: 1. Long-running tasks blocking web requests. 2. Considered simple cron-based processing. 3. Evaluated job queue systems (Sidekiq, Bull, Celery). 4. Assessed job priority and scheduling needs. 5. Thought about retry policies and failure handling. 6. Considered job monitoring and observability.

decision: Implement job queue using Redis with Bull for Node.js. Separate queues by priority. Configure exponential backoff for retries. Add job monitoring UI and dead letter queue analysis.

rejected_approaches: Inline processing: rejected as times out HTTP requests. Cron jobs: rejected as too slow for near-real-time processing.


scenario: Typography and font loading strategy

thought_process: 1. Custom fonts causing layout shift and slow loads. 2. Considered system fonts for performance. 3. Evaluated self-hosting vs CDN for web fonts. 4. Assessed font subsetting to reduce file size. 5. Thought about font-display strategy (swap, block, optional). 6. Considered FOUT (flash of unstyled text) vs FOIT (flash of invisible text).

decision: Use font-display: swap for body text, font-display: optional for decorative fonts. Subset fonts to include only needed characters. Self-host fonts for better performance control. Add font-face preconnect hints.

rejected_approaches: All fonts via Google Fonts: rejected as performance and privacy concerns. No custom fonts: rejected as limits brand expression.


scenario: Third-party dependency management

thought_process: 1. Security vulnerabilities in outdated dependencies. 2. Considered automated dependency updates (Dependabot, Renovate). 3. Evaluated manual update process. 4. Assessed semantic versioning trustworthiness. 5. Thought about breaking change detection. 6. Considered lockfile commit practices.

decision: Enable Dependabot for automated PRs. Configure auto-merge for patch/minor updates passing tests. Require manual review for major updates. Run security audits in CI. Commit lockfiles for reproducible builds.

rejected_approaches: No updates: rejected as security risk and missing improvements. Automatic all updates: rejected as breaking changes could cause issues.


scenario: Database replication strategy

thought_process: 1. Need to improve read performance and add disaster recovery. 2. Considered master-slave replication. 3. Evaluated multi-master replication for geographic distribution. 4. Assessed consistency requirements (staleness tolerance). 5. Thought about failover automation. 6. Considered replication lag monitoring.

decision: Implement single-master, multiple-read-replicas setup. Use read replicas for reporting and non-critical queries. Monitor replication lag and alert if > 5 seconds. Document failover procedure.

rejected_approaches: No replication: rejected as single point of failure. Multi-master: rejected as adds complexity with conflict resolution not currently needed.


scenario: Accessibility testing automation

thought_process: 1. Manual accessibility testing is time-consuming and error-prone. 2. Considered adding axe-core to automated tests. 3. Evaluated continuous integration accessibility scanning. 4. Assessed coverage needs (all pages vs critical flows). 5. Thought about false positive management. 6. Considered manual testing complementary approach.

decision: Integrate axe-core into end-to-end test suite. Scan all pages in CI for critical accessibility issues. Fix violations before merge. Supplement with quarterly manual testing by disabled users.

rejected_approaches: No automated testing: rejected as issues slip into production. Manual only: rejected as inconsistent and doesn't scale.


scenario: Progressive Web App (PWA) implementation

thought_process: 1. Mobile users experience poor connectivity. 2. Considered adding PWA capabilities for offline support. 3. Evaluated service worker implementation complexity. 4. Assessed installability and app-like experience benefits. 5. Thought about iOS support limitations. 6. Considered development overhead vs user benefit.

decision: Implement core PWA features: service worker for offline cache, manifest for installability, push notifications for engagement. Focus on critical offline functionality first. Test thoroughly on both Android and iOS.

rejected_approaches: Full offline capability: rejected as too complex for initial implementation. No PWA: rejected as poor mobile user experience.


scenario: Time zone handling in application

thought_process: 1. Users reporting scheduling issues due to time zones. 2. Considered storing all times in UTC. 3. Evaluated storing user time zone preference. 4. Assessed display logic for different time zones. 5. Thought about daylight saving time transitions. 6. Considered recurring event complexity.

decision: Store all times in UTC in database. Store user time zone preference. Convert to user's time zone on display. Use moment-timezone or date-fns-tz for timezone-aware calculations.

rejected_approaches: Server local time: rejected as breaks with distributed deployment. Client local time only: rejected as difficult to compare across users.


scenario: API gateway selection

thought_process: 1. Multiple microservices need unified entry point. 2. Considered building custom gateway service. 3. Evaluated managed API gateways (AWS API Gateway, Kong, Ambassador). 4. Assessed requirements: rate limiting, auth transformation, caching. 5. Thought about operational overhead. 6. Considered cost scaling patterns.

decision: Use AWS API Gateway for managed service with built-in features. Configure caching, throttling, and authorizers at gateway level. Use mapping templates for response transformation. Monitor costs and optimize.

rejected_approaches: Custom gateway: rejected as reinventing the wheel and operational burden. No gateway: rejected as cross-cutting concerns duplicated across services.


scenario: Environment configuration management

thought_process: 1. Configuration scattered across files and environment variables. 2. Considered .env files per environment. 3. Evaluated configuration services (Spring Cloud Config, Consul). 4. Assessed need for dynamic configuration updates. 5. Thought about secret separation from config. 6. Considered validation and type safety.

decision: Use environment variables for deployment-specific config. Validate config at application startup. Document required and optional variables. Use distinct configs for dev/staging/production environments.

rejected_approaches: Hardcoded config: rejected as inflexible and error-prone. Shared .env files: rejected as risk of committing secrets.


scenario: Real-time collaboration features

thought_process: 1. Need to add collaborative editing to application. 2. Considered simple WebSocket broadcasting of changes. 3. Evaluated CRDT (Conflict-free Replicated Data Types) approach. 4. Assessed conflict resolution requirements. 5. Thought about operational transformation algorithms. 6. Considered off-the-shelf solutions (Yjs, ShareDB).

decision: Implement using Yjs for CRDT-based collaboration. Use WebSocket provider for real-time updates. Add awareness features (cursors, presence). Persist document state with version history.

rejected_approaches: Last-write-wins: rejected as data loss with concurrent edits. Build from scratch: rejected as complex and error-prone.


scenario: Performance budget enforcement

thought_process: 1. Bundle size growing beyond acceptable limits. 2. Considered manual monitoring in PR reviews. 3. Evaluated automated bundle size checks in CI. 4. Assessed budget categories: total JS, CSS, images. 5. Thought about enforcement policy (block or warn). 6. Considered per-route budgets.

decision: Implement bundle size tracking in CI using bundlesize package. Set budgets for critical routes. Block PRs that exceed budgets by > 5%. Warn for minor overages. Display bundle size in PR comments.

rejected_approaches: No enforcement: rejected as bundle grows unbounded. Strict blocking: rejected as can block necessary features.


scenario: Feature branch naming conventions

thought_process: 1. Inconsistent branch names making git history confusing. 2. Considered free-form branch names. 3. Evaluated structured naming with prefixes (feature/, bugfix/, hotfix/). 4. Assessed integration with ticket systems. 5. Thought about branch deletion automation. 6. Considered commit message correlation.

decision: Implement naming convention: type/ticket-number-description. Examples: feature/PROJ-123-add-auth, bugfix/PROJ-456-fix-login. Validate in CI with branch name checker. Auto-delete branches after merge.

rejected_approaches: No convention: rejected as difficult to understand purpose. Overly complex: rejected as team won't follow consistently.


scenario: Database connection pooling configuration

thought_process: 1. Database connection exhaustion under load. 2. Analyzed current pool settings (too small). 3. Evaluated optimal pool size based on application server resources. 4. Assessed connection timeout and idle timeout settings. 5. Thought about connection leak detection. 6. Considered monitoring for pool exhaustion.

decision: Calculate optimal pool size: (cores * 2) + effective disk count. Set connection timeout to 30 seconds. Implement connection leak detection (max connection age). Monitor pool metrics and alert when > 80% used.

rejected_approaches: Unlimited connections: rejected as database will reject connections anyway. Very small pool: rejected as causes request queuing and slow response times.


scenario: Content Security Policy (CSP) implementation

thought_process: 1. Need to protect against XSS attacks. 2. Considered strict CSP blocking all inline scripts. 3. Evaluated report-only mode for testing. 4. Assessed third-party dependencies and script needs. 5. Thought about nonce or hash approach for inline scripts. 6. Considered browser compatibility.

decision: Start with CSP report-only mode to collect violations. Use strict-dynamic for script-src with nonces. Gradually tighten policy based on reports. Add specific allow-lists for required third-party domains.

rejected_approaches: Full blocking immediately: rejected as breaks functionality. No CSP: rejected as vulnerable to XSS attacks.