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Lessons (40)

• Clean Error Handling

  Fail loudly, fail early, and never swallow errors. Learn how to handle errors so bugs are easy to …

• Go Web Services with Gin

  … errors │ ├── service.go business rules (no Gin imports!) │ ├── repository.go interface + Postgres implementation │ └── handler.go Gin handlers: HTTP …

• Event-Driven Architecture

  … compensate I ✅ The flow and error handling are in one place. ❌ The mediator is extra coupling and a …

• Serverless: Lambda and API Gateway

  … Check other created resources separately. Practice: the handler passes a console test but API Gateway returns an error …

• Node.js and Express

  … routing, the middleware pipeline, validation, async error handling, project structure, configuration, security, rate limiting, logging and graceful shutdown …

• Event-Driven Patterns, Step Functions and Reliable Lambdas

  … See [Step Functions error handling](https://docs.aws.amazon.com/step-functions/latest/dg/concepts-error-handling.html …

• Behavioral Patterns II: Chain, Template, Iterator, Mediator, Memento, Visitor

  … Each handler either handles the request or passes it on. js // Express middleware IS a chain of responsibility …

• NestJS Core Concepts

  … middleware → guards → interceptors → pipes → handler → interceptors → filters on error. - Use a global ValidationPipe with DTOs, guards for auth …

• AI Evaluation, Safety, and Security

  Build representative tests, measure retrieval and model quality, defend against prompt injection, and handle sensitive data responsibly. The …

• React Hooks in Practice

  … the new one renders useActionState Handle form actions: pending state, result, errors useOptimistic Show the expected result instantly …

• Frontend Testing Strategy

  … Your components, hooks and data libraries run for real; only the server is fake. ts // mocks/handlers.ts …

• Rust: Types, Errors and Concurrency

  … when --- --- ? Propagate the error to the caller (most of the time) match / if let Handle each case differently …

• Backend Languages: Node.js, Go, Python & Rust

  … Docker and Kubernetes are written in Go) Verbose error handling, a smaller ecosystem than JS/Python Python async …

• Behavioral Patterns I: Observer, Strategy, Command, State

  … transition(order, action) { const handler = orderStates[order.status][action]; if (!handler) throw new Error( Cannot ${action} an order …

• Scalable Frontend Architecture

  … not each invent fetch calls, base URLs and error handling. Put transport and response conversion behind a feature …

• Consumers & Consumer Groups

  … how offsets are committed, and how to handle lag, errors and retries. The big idea A pile of …

• Async JavaScript: Promises, async/await and Node's Event Loop

  … running work in parallel, handling errors, timeouts and cancellation with AbortController, and how Node.js orders nextTick, microtasks …

• AWS Databases: Choose the Right One

  … managed SQL database RDS runs engines such as PostgreSQL and MySQL while AWS handles hardware, backups, and many …

• Delivery Guarantees: At-Most, At-Least & Exactly Once

  … catch (error) { await tx.abort(); // nothing written, offset not committed → the message will be retried throw error; } }, }); Consumers …

• Atomic Design & Component Libraries

  … Prefer the browser's native element before recreating it with div plus click handlers. tsx type IconButtonProps = { label …

• Database Indexing & Transactions

  … call or user input inside one. - Always handle rollback on errors (most ORMs do this for you). - Lock …

• Edge, Platform & Frontend Delivery

  … Monitor error rate, Web Vitals and server latency after release. 5. Roll back to the previous known-good …

• Prompting and Structured Outputs

  … library or provider-supported schema enforcement, handle refusal and parsing errors, and do not cast untrusted output into …

• Concurrency, Resilience & Distributed Workflows

  … Idempotency is required for retryable HTTP requests, queue consumers, scheduled jobs and webhook handlers. Retries, exponential backoff and …

• JavaScript Language Fundamentals

  … objects and prototypes, classes, modules, array methods and error handling. The big idea JavaScript has only a few …

• Domains, Load Balancers and HTTPS

  … http.server import BaseHTTPRequestHandler, HTTPServer import json class Handler(BaseHTTPRequestHandler): def do GET(self): if self.path == "/health …

• Testing, Preconditions, and Policy Checks

  Use validation, lifecycle conditions, Terraform tests, and policy checks to catch different classes of errors. Different checks answer …

• React Internals & Concurrent Rendering

  … Rendering may happen more than once; network calls and other side effects belong in event handlers, effects, or …

• AWS: Start Here

  … With a managed database, AWS handles more infrastructure work, but you still choose network access, credentials, backup settings …

• Go Concurrency: Goroutines, Channels and Context

  … messages: handle(msg) case err := <-errs: return err case <-time.After(2 time.Second): return errors.New("timeout …

• CI/CD and Reviewed Production Changes

  … 1 means an error, and 2 means changes exist. Configure the scheduler to handle 2 as a drift …

• Scaling, Load Balancing & Rate Limiting

  … It gives clients one stable address while it decides which healthy backend should handle each connection or request …

• Premiere-Night Video Streaming

  … img/system-design-l6/premiere-streaming.svg) Plane Handles Goal --- --- --- Control Auth, entitlement, manifest, progress Small, stateless, scalable …

• Go Fundamentals

  … with value or pointer receivers, implicit interfaces, explicit error handling with wrapping, defer/panic/recover, and generics. The …

• Timeouts, Retries & Backpressure

  … latency, retries, and error-budget burn. A concrete overload plan Imagine image processing can handle 100 jobs at …

• Message Delivery: Queues, Kafka, Ordering and DLQs

  … Bound retries and quarantine poison events with original payload, error and metadata. Define who repairs and replays them …

• YAGNI: You Aren't Gonna Need It

  … Clear names and structure Generic BaseAbstractManager<T classes Error handling and security Caching layer before measuring slowness Code …

• KISS: Keep It Simple, Stupid

  … Too simple. KISS doesn't mean skipping validation, error handling or tests. Key takeaways - The simplest solution that …

• Python and Math Foundations with Runnable Examples

  … In production, handle zero denominators explicitly and report results for relevant classes and groups. What math should you …

• Backend Design Scenarios

  … Route only replica-safe reads and handle replication lag. 4. Shard when the primary cannot handle the write …