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Lessons (40)

• Topics, Partitions & Offsets

  How Kafka organises data. Why topics are split into partitions, how message keys decide the partition and keep …

• Consumers & Consumer Groups

  … This is the committed offset , saved in Kafka's internal consumer offsets topic. If a consumer crashes, its …

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

  … async ({ topic, partition, message }) = { const tx = await producer.transaction(); try { await tx.send({ topic: "ledger", messages: [{ key: message …

• Heaps & Priority Queues

  … keep a min-heap of size k . The heap's root is the smallest of the top k …

• What Is Apache Kafka?

  … append an event const producer = kafka.producer(); await producer.connect(); await producer.send({ topic: "orders", messages: [{ key: "customer …

• Stacks & Queues

  … top is running)"] direction TB c["c() ⬅ running"] --- b["b()"] --- a["a()"] --- g["global"] end Infinite recursion keeps …

• Event-Driven Architecture

  … Broker vs mediator topologies, the four kinds of event patterns, event design, and the real trade-offs. The …

• Kafka vs RabbitMQ & the Kafka Ecosystem

  … direct, topic, fanout, headers exchanges Simple: topic + partition by key Ordering Per queue (with one consumer) Per partition …

• Scaling & Health Probes

  … scale consumers on Kafka lag triggers: - type: kafka metadata: bootstrapServers: kafka:9092 consumerGroup: email-service topic: shop.orders …

• Brokers, Replication & Durability

  … Keep it false for important topics.) The controller and KRaft One broker acts as the controller : it tracks …

• Dynamic Programming

  … add a memo (top-down DP) → optionally convert it to a table (bottom-up). Key takeaways - DP = recursion …

• Graphs: BFS & DFS

  … stack / recursion) = go deep, backtrack = cycles, components, topological sort. - Always keep a visited set, or cycles will loop …

• Which Pattern Do I Need?

  … Microservices and Kafka lessons: Object-level pattern System-level cousin --- --- Observer Pub/Sub, Kafka topics, event-driven architecture …

• Comments & Formatting

  … important things at the top, details below](/img/clean-code/newspaper.svg) Vertical order: top-down, like a …

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

  … the king of AI/data; FastAPI for modern APIs, Django for full-featured apps. - Rust: top performance with …

• DSA Interview Patterns Cheat Sheet

  … all / connected / cycles DFS[DFS] C -- no D{Top K / min / max<br/ repeatedly?} D -- yes H[Heap …

• Structural Patterns: How to Connect Objects

  … Each topping wraps the drink, adds something (price, flavour), and it's still a coffee. Problem: add responsibilities …

• How Browsers Render a Page

  … Read the blueprint (HTML) → know which rooms exist ( DOM ). 2. Read the interior design notes (CSS) → know the …

• Trees & Binary Search Trees

  … one person at the top, each person has zero or more people below them, and nobody reports to …

• Message Queues & RabbitMQ

  … Routing rule Example --- --- --- Direct Exact routing key match "pdf" → pdf-queue Topic Wildcards: = one word, = zero or more …

• Authentication, Authorization & API Security

  … A 401 Unauthorized means "I don't know who you are". A 403 Forbidden means "I know who …

• Helm, kubectl Cheat Sheet & Best Practices

  … kubectl rollout restart deploy/shop-api Resource usage kubectl top pods / kubectl top nodes Recent events kubectl get …

• React Hooks in Practice

  … context during render (with Suspense) Key takeaways - Call hooks at the top level, in the same order every …

• Vertical Slice Architecture & the Modular Monolith

  … network call. Key takeaways - Vertical slices organise code by feature: one folder per use case, top to bottom …

• SOLID at a Glance

  Five design principles that keep object-oriented and modular code easy to extend, test and change. One picture …

• Clean Architecture in Depth

  … can know anything about something in an outer circle, not even its name. 💡 The Clean Code topic has …

• Small Functions That Do One Thing

  … No "and" in its description. - The top-level function should read like a table of contents. - Keep one …

• Clean Error Handling

  … Fail fast with guard clauses Check bad input at the top of the function and exit immediately. This …

• Code Smells & Refactoring

  … which currency? cents or dollars? rounding? function addTax(price) { return price 1.2; } // ✅ A small object that knows …

• Clean Architecture

  … Inner layers never know about outer layers. 🏛️ Want to go deeper? This lesson is the introduction. The …

• Monolith vs Microservices

  … payments must keep working when recommendations are down. ❌ Bad reasons: - "Netflix does it." (Netflix has thousands of engineers …

• Big-O Notation Made Simple

  … average O(n log n), worst O(n²) with bad pivots. Key takeaways - Big-O = how work grows …

• Kafka Producers

  … topic: "shop.orders.placed", acks: -1, // all in-sync replicas compression: CompressionTypes.GZIP, messages: [ { key: order.id, // keeps …

• Finding Service Boundaries with DDD

  … architecture/ddd-tactical-design) in the Software Architecture topic. Key DDD vocabulary Term Meaning Example --- --- --- Domain The business …

• Scaling, Load Balancing & Rate Limiting

  … the key to scaling out If a server keeps user sessions in its own memory , the next request …

• Frontend Security

  … Clickjacking An evil page loads your site in an invisible iframe on top of a fake "Win a …

• Sorting Algorithms

  … That matters when you sort by several keys. The simple O(n²) sorts Bubble sort: big items "bubble …

• Choosing an Architecture

  … Hexagonal, Stripe behind an ACL"] b1((core)) -- b2[Stripe adapter] end end Mono -- events via outbox K[(Kafka …

• Caching & Redis

  … Hot key One key (a celebrity's profile) gets so much traffic it overloads a single Redis node …

• Hexagonal Architecture (Ports & Adapters)

  … Cockburn drew a hexagon to escape the "top-to-bottom layers" picture, and to show there are many …