Microservices architecture is an approach where a single application is developed as a suite of small, independent services. Each service runs in its own process and communicates with others, often using lightweight mechanisms like HTTP APIs. The core principle is that these services are loosely coupled, built around specific business capabilities, and are independently deployable, scalable, and maintainable. This contrasts with a monolithic architecture where all components are tightly integrated into a single, large codebase and deployed as one unit. The independent nature of microservices improves fault isolation and allows for faster, more frequent deployments.

A. This describes a monolithic application, where all layers are packaged together, rather than a distributed system of individual services.
C. This is the definition of a monolithic architecture, which is characterized by tight coupling and deployment as a single unit, the opposite of microservices.
D. This is a generic description of web services or APIs. While microservices use this communication method, it omits the core architectural principles of loose coupling and independent deployability.

1. Cisco DevNet

"Introduction to Microservices": "A microservice is a small

loosely coupled

distributed service. Microservices allow you to take a large application and decompose or break it into easily manageable small components with narrowly defined responsibilities... Because they are loosely coupled

you can update

deploy

and scale them independently." This source directly validates the concepts of "loosely coupled" and "independently deployable".

(Source: Cisco DevNet Learning Labs

Introduction to Microservices module)

2. Microsoft Azure Documentation

"What are microservices?": "Microservices are a software development technique—a variant of the service-oriented architecture (SOA) architectural style that structures an application as a collection of loosely coupled services. In a microservices architecture

services are fine-grained and the protocols are lightweight." This official vendor documentation explicitly defines microservices using the term "loosely coupled services".

(Source: Microsoft Azure Architecture Center

Microservices architecture style section)

3. Amazon Web Services (AWS) Documentation

"What are Microservices?": "Microservices are an architectural and organizational approach to software development where software is composed of small independent services that communicate over well-defined APIs... This architecture allows for services to be created

deployed

and maintained independently." This source reinforces that services are independent and can be maintained and deployed separately.

(Source: AWS

"What are Microservices?" whitepaper)