Design Your Workload Service Architecture - Reliability Pillar

Design Your Workload Service Architecture

Build highly scalable and reliable workloads using a service-oriented architecture (SOA) or a microservices architecture. Service-oriented architecture (SOA) is the practice of making software components reusable via service interfaces. Microservices architecture goes further to make components smaller and simpler.

Service-oriented architecture (SOA) interfaces use common communication standards so that they can be rapidly incorporated into new workloads. SOA replaced the practice of building monolith architectures, which consisted of interdependent, indivisible units.

At AWS, we have always used SOA, but have now embraced building our systems using microservices. While microservices have several attractive qualities, the most important benefit for availability is that microservices are smaller and simpler. They allow you to differentiate the availability required of different services, and thereby focus investments more specifically to the microservices that have the greatest availability needs. For example, to deliver product information pages on Amazon.com (“detail pages”), hundreds of microservices are invoked to build discrete portions of the page. While there are a few services that must be available to provide the price and the product details, the vast majority of content on the page can simply be excluded if the service isn’t available. Even such things as photos and reviews are not required to provide an experience where a customer can buy a product.

Choose how to segment your workload: Monolithic architecture should be avoided. Instead, you should choose between SOA and microservices. When making each choice, balance the benefits against the complexities—what is right for a new product racing to first launch is different than what a workload built to scale from the start needs. The benefits of using smaller segments include greater agility, organizational flexibility, and scalability. Complexities include possible increased latency, more complex debugging, and increased operational burden.

Even if you choose to start with a monolith architecture, you must ensure that it’s modular and has the ability to ultimately evolve to SOA or microservices as your product scales with user adoption. SOA and microservices offer respectively smaller segmentation, which is preferred as a modern scalable and reliable architecture, but there are trade-offs to consider especially, when deploying a microservice architecture. One is that you now have a distributed compute architecture that can make it harder to achieve user latency requirements and there is additional complexity in debugging and tracing of user interactions. AWS X-Ray can be used to assist you in solving this problem. Another effect to consider is increased operational complexity as you proliferate the number of applications that you are managing, which requires the deployment of multiple independency components.

Figure 3: Monolithic architecture versus microservices architecture

Build services focused on specific business domains and functionality: SOA builds services with well-delineated functions defined by business needs. Microservices use domain models and bounded context to limit this further so that each service does just one thing. Focusing on specific functionality enables you to differentiate the reliability requirements of different services, and target investments more specifically. A concise business problem and small team associated with each service also enables easier organizational scaling.

In designing a microservice architecture, it’s helpful to use Domain-Driven Design (DDD) to model the business problem using entities. For example for Amazon.com entities may include package, delivery, schedule, price, discount, and currency. Then the model is further divided into smaller models using Bounded Context, where entities that share similar features and attributes are grouped together. So using the Amazon example package, delivery and schedule would be part of the shipping context, while price, discount, and currency are part of the pricing context. With the model divided into contexts, a template for how to boundary microservices emerges.

Provide service contracts per API: Service contracts are documented agreements between teams on service integration and include a machine-readable API definition, rate limits, and performance expectations. A versioning strategy allows clients to continue using the existing API and migrate their applications to the newer API when they are ready. Deployment can happen anytime, as long as the contract is not violated. The service provider team can use the technology stack of their choice to satisfy the API contract. Similarly, the service consumer can use their own technology.

Microservices take the concept of SOA to the point of creating services that have a minimal set of functionality. Each service publishes an API and design goals, limits, and other considerations for using the service. This establishes a “contract” with calling applications. This accomplishes three main benefits:

  • The service has a concise business problem to be served and a small team that owns the business problem. This allows for better organizational scaling.

  • The team can deploy at any time as long as they meet their API and other “contract” requirements.

  • The team can use any technology stack they want to as long as they meet their API and other “contract” requirements.

Amazon API Gateway is a fully managed service that makes it easy for developers to create, publish, maintain, monitor, and secure APIs at any scale. It handles all the tasks involved in accepting and processing up to hundreds of thousands of concurrent API calls, including traffic management, authorization and access control, monitoring, and API version management. Using OpenAPI Specification (OAS), formerly known as the Swagger Specification, you can define your API contract and import it into API Gateway. With API Gateway, you can then version and deploy the APIs.