Modular Monolith

Answer-First: A Modular Monolith prevents code degradation (“Big Ball of Mud”) by applying Domain-Driven Design (DDD) Bounded Contexts, isolating database schema namespaces (e.g. billing.payments, inventory.stock), enforcing compile-time import boundaries via Go internal packages and arch-go, and using an in-memory transactional outbox pattern for asynchronous event communication. Pillar Architecture Guide: This article is part of the Architecting 21-Service E-commerce with Golang & DDD series and Composable E-Commerce Migration guide. Please refer to the original article for a detailed overview of the architecture. ...

Answer-first: Extracting a module from a modular monolith into an independent microservice is justified only when domain isolation, asymmetric CPU/RAM scaling, or strict regulatory isolation demands it. Having pre-enforced DDD bounded contexts ensures extraction requires introducing network RPC adapters (gRPC) and Anti-Corruption Layers rather than refactoring internal core domain logic. Pillar Architecture Guide: This article is part of the Architecting 21-Service E-commerce with Golang & DDD series and Composable E-Commerce Migration guide. Please refer to the original article for a detailed technical overview of the architecture. ...

Answer-First: Consolidating fragmented microservices back into a modular monolith utilizes the Reverse Strangler Fig pattern with dual-writing and zero-downtime database schema mergers. Merging database schemas using logical schema separation (PostgreSQL schemas) preserves strict module autonomy while eliminating distributed transaction complexity. Pillar Architecture Guide: This article is part of the Architecting 21-Service E-commerce with Golang & DDD series and Composable E-Commerce Migration guide. Please refer to the original article for an architectural overview of the architecture. ...

Answer-first: The Modular Monolith case study matrix evaluates how industry leaders—including Shopify, GitHub, Segment, Etsy, and Stack Overflow—scale core systems using monolithic architecture. These real-world production benchmarks prove that co-locating domains reduces infrastructure expenses, deployment friction, and network latency while maintaining high development velocity. Pillar Architecture Guide: This article is part of the Architecting 21-Service E-commerce with Golang & DDD series and Composable E-Commerce Migration guide. Please refer to the original article for a detailed technical overview of the architecture. ...

Answer-First: Large monoliths avoid slow CI/CD pipelines by implementing monorepo path-filtering, Go build caching, and selective test execution based on git diffs. Deploying a single-binary modular monolith enables atomic deployments where application code and schema migrations ship deterministically in a single commit release. Pillar Architecture Guide: This article is part of the Architecting 21-Service E-commerce with Golang & DDD series and Composable E-Commerce Migration guide. Please refer to the original article for a detailed overview of the architecture. ...

Pillar Architecture Guide: This article is part of the Architecting 21-Service E-commerce with Golang & DDD series. Please refer to the original article for a detailed overview of the architecture. Prerequisite: This is the executive summary and introductory overview of the Modular Monolith Architecture series. No prior reading is required to start here. Part 0: Executive Summary — How Amazon Prime Video Saved 90% on Infrastructure Costs Executive Summary & Quick Answer: Amazon Prime Video reduced infrastructure costs by 90% by consolidating their audio/video monitoring service from serverless AWS Lambda/Step Functions into a single modular monolith. This transition eliminated high-frequency state transition fees and S3 network egress bottlenecks, demonstrating that in-memory data processing outperforms distributed microservices for high-throughput workloads. ...

Answer-First: Observability in modular monoliths leverages in-process OpenTelemetry span propagation across module boundaries without network serialization overhead. Combining in-memory context tracking with structured logging reduces telemetry ingestion costs while retaining microservice-level latency visibility. Pillar Architecture Guide: This article is part of the Architecting 21-Service E-commerce with Golang & DDD series and Composable E-Commerce Migration guide. Please refer to the original article for an architectural overview of the architecture. Prerequisite: Before reading this part, please review Part 4: CI/CD Simplified. ...

Pillar Architecture Guide: This article is part of the Architecting 21-Service E-commerce with Golang & DDD series and Composable E-Commerce Migration guide. Please refer to the original article for a detailed overview of the architecture. Prerequisite: Before reading this part, please review Part 1: Architectural Decision Framework. Part 2: FinOps Cost Reality - The “Hidden Tax” of Microservices Executive Summary & Quick Answer: The true cost of microservices lies in hidden infrastructure charges: sidecar proxy memory overhead, cross-AZ data transfer egress fees, NAT Gateway processing fees, and high-cardinality logging ingestion. A modular monolith co-locates processing within the same private subnet and container task, bypassing these multi-thousand-dollar cloud bills entirely. ...

Pillar Architecture Guide: This article is part of the Architecting 21-Service E-commerce with Golang & DDD series and Composable E-Commerce Migration guide. Please refer to the original article for a detailed overview of the architecture. Prerequisite: Before reading this part, please review Part 0: Executive Summary — How Amazon Prime Video Saved 90% on Infrastructure. Part 1: Architectural Decision Framework Executive Summary & Quick Answer: Deciding between a Modular Monolith and Microservices depends on organizational scale, transaction consistency requirements, and latency limits. Teams with under 50 developers should build a modular monolith to avoid the administrative and operational “microservice premium”, using direct memory function calls to bypass network latency and complex distributed transaction protocols. ...