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Build reliable client–service integrations by understanding DNS, transport, HTTP caching, URI resolution, typed payloads, authorization and retry contracts. Repair and review real protocol and compatibility defects.
The curriculum and complete lessons are free with an account. Optional practice resources and Ono usage follow your plan’s allowances.
Follow a request from naming and transport to representation, caching and recoverable mutation. Protocol exercises are paired with reviews of plausible but incomplete fixes.
How to study: Work in order. Predict the result before opening a visualizer, implement before reading the editorial, and explain the invariant and edge cases after each exercise. Repository and review activities are paired: fix the behavior, then assess a proposed change independently. Choose a supported language or repository environment; you do not need to repeat every environment. Existing completion of shared content counts toward this path.
Check your understanding: • Distinguish user input, a URI reference, a cache key and a resource identity. • Test missing versus empty headers, validators, conditional requests and schema evolution. • Explain what a timeout means for safe retries and visible effects.
The TCP/IP Model: The Internet's Architectural Blueprint
Ports
Sockets
TCP Protocol Overview
TCP Three-Way Handshake
TCP Timers: The Temporal Guardians of Reliable Communication
TCP Dynamic Timeout Mechanisms
DNS Overview
DNS Records: The Data Backbone of Domain Name Resolution
DNS Resolution
DNS Caching Mechanisms
HTTP Overview
HTTP Methods and Status
DNS Hierarchy
DNS Security: Protecting Domain Name Resolution
Client-Server Model
APIs and Protocols
Canonicalize DNS master-file owner names
Canonicalize DNS master-file owner names
Use the closest DNS encloser for wildcard synthesis
Use the closest DNS encloser for wildcard synthesis
Resolve alias targets without chasing CNAME queries
Return CNAME RRsets while misqualifying absolute targets
Merge relative paths with the base directory, replacing its final file segment
uri proposal 1
Remove literal dot segments including terminal dot and parent segments while preserving duplicate slashes and percent-encoded dot text
uri proposal 2
An explicitly empty query replaces the base query
uri proposal 3
HTTP/1.1: The Foundation of Modern Web Communication
HTTP/2: The Modern Web Protocol
HTTP/3 - The Next Generation of Web Protocol
HTTPS and Web Security
TLS Handshake
Certificates and PKI
Request-Response Pattern
REST API Design
API Versioning: Managing Change in Distributed Systems
Network-path references replace authority, and fragments always come from the reference
uri proposal 4
An explicit absolute reference replaces the base scheme and normalizes scheme case
uri proposal 5
Why Caching Matters
Caching Layers
Write-Through Caching
Cache Invalidation Strategies
CDN Caching: Global Content Distribution at Scale
Repair shared freshness directives
Repair shared freshness directives
Include response delay in corrected age
Include response delay in corrected age
Preserve absent headers in variant identities
Preserve absent headers in variant identities
Repair entity-tag strength and condition precedence
Repair entity-tag strength and condition precedence
Repair 304 body retention and connection metadata
Repair 304 body retention and connection metadata
Data Transfer Object (DTO) Design
Validation and Defensive Programming
Error Handling in APIs
The Principle of Least Astonishment (POLA)
Restore directional numeric schema widening
Restore directional numeric schema widening
Require every writer union branch to be readable
Require every writer union branch to be readable
Resolve reader aliases without losing renamed values
Resolve reader aliases without losing renamed values
Preserve explicit null defaults and validate default types
Preserve explicit null defaults and validate default types
Apply enum fallbacks and validate their declarations
Apply enum fallbacks and validate their declarations
Preconditions and Postconditions
Immutable Objects — Unchanging by Design
Defensive Copying: Preserving Object Integrity
Unit of Work Pattern
Decode JSON Pointer escapes exactly once
Decode JSON Pointer escapes exactly once
Insert array elements without replacing their neighbours
Insert array elements without replacing their neighbours
Compare JSON values structurally in test operations
Compare JSON values structurally in test operations
Reject descendant moves and roll back failed patch batches
Restore batch rollback while deleting a move source before ancestry validation
Apply recursive merge deletion with safe object keys
Delete merge-patch null members while accepting unsafe keys
Authentication Patterns in Distributed Systems
Authorization Patterns
OAuth2 and OpenID Connect
JWT Tokens
API Security
Data Protection
Temporary access remains valid at its expiry time
Expire access at the deadline
A read-only grant unexpectedly permits writes
Capture the scopes the applicant requested
Reject boolean offsets before redacting a document
Reject booleans before accepting integer offsets
Add stable document-local aliases for sensitive values
Scope redaction aliases to both kind and exact value
Timeout Patterns in Synchronous Communication
Retry with Backoff: Building Resilient Distributed Systems
Rate Limiting at API Gateway
Circuit Breaker Pattern: Building Resilient Distributed Systems
Outbox Pattern
Delivery Guarantees
Scope credit accounts and retry receipts to the tenant
Separate credit account keys while leaving retry receipts shared
Failed notification commits leave a delivered message
Deliver queued notifications only
Design an API Gateway
Design a Rate Limiter
API Documentation
Distributed Tracing: Following Requests Across Services
Integration Testing at LLD Level
Documentation and Communication
Release choices put version 1.10 before 1.2
Compare release components instead of version labels
Implement maintenance-window upgrade planning
Plan upgrades while checking only the final release
Failed certificate rotation changes the active credential
Reject stale certificate rotations
Complete this path to earn a personalised certificate. You choose whether to make it public.