Microservices, also known as the microservice architecture, is an architectural style that structures an application as a collection of services. These encapsulated services, collectively known as a “microservice,” can operate and evolve independently. Design principles for microservices are crucial for building effective applications using this architectural style. These principles are even more crucial if you’re pursuing the AWS Certified Solution Architect – Associate (SAA-C03) exam, as it tests your skills in designing and deploying scalable, highly available, and fault-tolerant systems on AWS, among other things.

Table of Contents

Single Responsibility Principle

The single responsibility principle is a fundamental design principle in microservices. In the context of microservices, this principle suggests that each microservice within the application should have only one job. This can be illustrated by segmenting services by business function, such as order management, customer management, and so on.

On AWS, for example, each AWS Lambda function should conform to this principle by fulfilling only one clearly defined task.

Stateless and Stateful Microservices

In microservices architecture, there are two types of workloads, stateless and stateful. A stateless workload doesn’t remember anything from one execution to the next. Every request is handled based on the given input, which means that it doesn’t aggregate data over multiple requests. In contrast, a stateful workload retains data across multiple requests. Here’s a simple comparison:

Stateless Workloads Stateful Workloads
Data is not preserved between requests Data is preserved between requests
Better scalability Risks of data inconsistency and requires more resources
Cannot leverage previous interactions Can leverage previous interactions
Examples: RESTful APIs, AWS Lambda Examples: Databases, AWS ElastiCache

Scalable and Resilient Microservices

Microservices need to be scalable and resilient. Scalability refers to the ability of a microservice to handle increasing amounts of work by adding resources. AWS, for instance, provides several native services that aid in scalability, like EC2 Auto Scaling and Elastic Load Balancing.

Resilience is the ability of a microservice to cope with failures and remain functional. Microservice should be designed with the assumption that services could fail. AWS Service like Amazon CloudWatch can handle monitoring and error logging to ensure that problems are promptly addressed.

Decentralized Governance

In a microservices architecture, each microservice should be able to use technology that is best suited to its needs. This means a decentralized governance model, where teams have the freedom to choose technologies. This can mean different languages, databases, and tools for different services.

AWS provides a comprehensive and broad range of services that different teams within a business can choose for their specific needs.


Design principles like single responsibility, stateless vs stateful workloads, scalability, resilience, and decentralized governance are instrumental to devise and maintain effective microservices. Understanding these principles is vital for practitioners, especially for those preparing for AWS Certified Solutions Architect – Associate (SAA-C03) exam.

In AWS, you have a wide variety of services available that conform to these design principles, allowing for the creation of robust, efficient, and reliable applications using the microservices architecture.

Practice Test

True or False: Stateless workload is recommended over stateful workload in microservices design.

  • True
  • False

Answer: True.

Explanation: Stateless applications can scale horizontally because they don’t save the client’s session data. This makes stateless applications far easier to scale as compared to their stateful counterparts.

In microservices, what does the term ‘stateless’ refer to?

  • A. A service that maintains client information
  • B. A service that does not maintain client information
  • C. A service that continuously verifies client information.

Answer: B. A service that does not maintain client information.

Explanation: In stateless design, each request from client to server must contain all the information needed to service the request, and the server should not store anything between requests.

What does the principle of ‘Single Responsibility’ in microservices refer to?

  • A. One function per service
  • B. One function per container
  • C. One function per database

Answer: A. One function per service

Explanation: The Single Responsibility Principle means that one service or module should have only one reason to change.

Is deploying microservices in a monolithic architecture a good design principle?

  • Yes
  • No

Answer: No.

Explanation: Microservices architecture allows for the breakdown of tasks into smaller, more manageable pieces that can be developed and managed separately. Deploying them in monolithic architecture would defeat their purpose.

True or False: Microservices are typically deployed with a centralized database.

  • True
  • False

Answer: False.

Explanation: Typically, each microservice has its own database to ensure decoupling from other services.

What is the benefit of implementing automation in microservices design and deployment?

  • A. Reduced human error
  • B. Increased cost
  • C. Time-consuming

Answer: A. Reduced human error

Explanation: Automation makes processes repeatable, and reduces the chance of human error.

Loose coupling and high cohesion refers to:

  • A. Making services as dependent as possible
  • B. Making services as independent as possible
  • C. Having a mix of dependent and independent services

Answer: B. Making services as independent as possible

Explanation: Loose coupling encourages having each service as independent as possible while high cohesion keeps related services together.

True or False: Observeability is not significant in microservices architecture.

  • True
  • False

Answer: False

Explanation: Observability is crucial in microservices as it allows monitoring and understanding the state and performance of the services.

The ‘Backends for Frontends’ pattern in microservices allows:

  • A. A single backend for all types of clients
  • B. Each frontend (like mobile, desktop, etc.) to have its own backend
  • C. All backends to be dependent on frontends

Answer: B. Each frontend (like mobile, desktop, etc.) to have its own backend

Explanation: This approach allows the team to tailor the backend according to the specific requirements of each client.

True or False: Each microservice should have its own data-model.

  • True
  • False

Answer: True

Explanation: It helps in separation of concerns and loose coupling by ensuring that each microservice doesn’t depend on others for its data requirements.

Interview Questions

What is the major advantage of using stateless workloads in microservices architecture?

The primary advantage of using stateless workloads is that they can be easily scaled horizontally by adding or removing instances of the service without impacting the system’s behavior.

What influences the decision to choose between stateless and stateful microservices?

The decision to choose between stateless and stateful microservices is typically influenced by the requirements of the application, the kind of data it handles, its scalability requirements, and its interaction with other services and components.

What is the primary principle behind designing microservices?

The primary principle behind designing microservices is the Single Responsibility Principle. Each microservice is responsible for a single specific business functionality and can operate independently.

How does data consistency get managed in a stateless microservice architecture?

In a stateless microservice architecture, data consistency is handled through methods such as database transactions or eventually consistent mechanisms like event-driven architectures.

What does it mean that microservices should be loosely coupled?

If microservices are loosely coupled, changes to one service have minimal impact on other services. This allows for faster deployments, lower risk of system-wide failure, and independent service scalability and development.

What is the main challenge of handling stateful workloads in microservices?

The main challenge with stateful workloads is that they cannot be simply scaled horizontally due to the requirement to maintain state or data continuity across sessions. This can limit flexibility and scalability.

How is resilience achieved in microservice architecture design?

Resilience in microservice architecture design is achieved through features like timeouts, retries, fallbacks, and circuit breakers that allow the system to function even when some parts of it fail.

What is the advantage of designing microservices with a Domain-Driven Design approach?

A Domain-Driven Design approach segregates the system into different domains or business capabilities, allowing developers to focus on the business logic instead of on infrastructural complexities.

What is the role of APIs in a microservices architecture?

APIs in a microservices architecture enable communication and data exchange between different services and components, thereby fostering decoupling and independence.

How can data consistency be achieved in a distributed microservice system?

In a distributed microservice system, data consistency can be achieved through mechanisms like event sourcing, distributed transactions, or the Saga pattern.

Why is automation an essential aspect of microservices design?

Due to the decomposition of applications into smaller services, the need for deployment, scaling, monitoring, and management processes increases, making automation essential for operational efficiency.

In microservices, how is fault isolation achieved?

In microservices, fault isolation is achieved through their inherent design which limits the scope of failure to a particular service only. This way, even if one service fails, others can still function independently.

Why is Containerization beneficial in the deployment of microservices?

Containerization provides a consistent environment for running microservices, regardless of the hosting environment, which greatly simplifies deployment, scaling, and management.

Which principle allows microservices to evolve without interrupting the user experience?

The principle of evolutionary design allows microservices to grow and adapt to new requirements and technologies without disturbing the user experience.

What AWS service can be used to deploy microservices?

AWS services like Elastic Beanstalk, EC2, Lambda, and Amazon ECS (Elastic Container Service) can be used for deploying microservices.

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