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Code → runtime → application → system

Backend

How server code executes, how NestJS assembles an application, and how a backend system stays responsive as load and complexity grow.

Chapters
17
Learning tracks
5
PRODUCTION CASES
19

What this sphere covers

Node.js Runtime

Event Loop · libuv · Worker Threads

07
  1. CHAPTER 01Event Loop orderStack → queues → phases

    Compare synchronous code, nextTick, microtasks, timers, poll, and check in one live run.

  2. CHAPTER 02Event demultiplexerMany sources → one thread

    Start a timer, file read, and DNS lookup together, then observe ready callbacks returning to JavaScript.

  3. CHAPTER 03Callback queueOne stack, many ready tasks

    Five zero-delay timers show how one expensive callback delays the entire queue.

  4. CHAPTER 04Blocking vs WorkerCPU-bound work

    Compare heartbeat gaps and a real HTTP load test with CPU work on main versus a bounded Worker pool.

  5. CHAPTER 05libuv thread poolHidden parallelism

    Six PBKDF2 jobs reveal the native thread-pool queue and the callbacks returning to the Event Loop.

  6. CHAPTER 07Promises, setImmediate, and BullMQMicrotasks → check → Redis jobs

    Practice Promise chains, async/await, combinators, and setImmediate, then follow a real BullMQ job lifecycle through Redis.

  7. CHAPTER 08Node.js vs Java, Go, and PythonConcurrency model → suitable workload

    Learn why Node is efficient for I/O, where the Event Loop advantage ends, and which models Java, Go, and Python provide.

Memory and diagnostics

leaks · closures · GC · heap snapshots

02
  1. CHAPTER 06Memory leakRetained references → rising RSS

    A controlled leak in an isolated process: watch heap, external, and RSS, release references, and then run GC.

  2. CHAPTER 09Closures, GC, and heap snapshotsRetainer path → proven cause

    Reproduce a leak through a closure or global cache, capture the heap, and find the retention path from payload to GC root.

NestJS

DI · IoC · request lifecycle

02
  1. CHAPTER 11NestJS Dependency Injection and IoCModule metadata → tokens → instances

    Build a real Nest application context and inspect class, value, factory, alias, singleton, and request-scoped providers.

  2. CHAPTER 12NestJS request lifecycleMiddleware → policy → handler → outcome

    Send real requests through Nest middleware, guards, interceptors, pipes, a controller, service, and exception filter.

Architecture

microservices · caching · System Design

03
  1. CHAPTER 13Microservices: boundaries, messages, and failuresCapability → contract → transport

    Understand why services are separated, how commands and events cross a network, and which failure modes distributed systems introduce.

  2. CHAPTER 21Caching in Node.js, NestJS, Redis, and HTTPKey → hit/miss → invalidation

    Learn where caching removes repeated work, how cache-aside behaves, and how stale data, stampedes, and unbounded memory cause incidents.

  3. CHAPTER 25System Design foundationsRequirements → scale → state → failures

    Learn to turn product requirements into capacity estimates, data flows, reliability boundaries, and testable trade-offs.

Python and CPython

syntax · objects · GIL · asyncio

03
  1. CHAPTER 22Python syntax for a JavaScript developerRead Python without guessing

    Learn the minimum syntax, collections, control flow, functions, and module rules needed to read everyday Python code.

  2. CHAPTER 23Python objects, functions, and protocolsIdentity · classes · generators · errors

    Read functions as values, classes, dataclasses, generators, decorators, exceptions, and context managers without importing JavaScript assumptions.

  3. CHAPTER 24CPython runtime, memory, GIL, and asyncioSource → bytecode → frames → concurrency

    Trace how CPython compiles and executes code, owns objects, collects cycles, coordinates threads, and schedules asyncio tasks.