Some questions on microservices
- 1. Some Q/A on Microservices Architecture in Enterprise Applications Context Pranab Das
- 2. What are Some of the Characteristics of Enterprise Applications? Run Information System (IS) of large businesses e.g., banking, insurance, etc. Have large user bases for their transactional systems with heavy concurrent loads. Store data in polyglot systems e.g., Mainframe, RDBMS, Document DB, (K, V) pairs, Graph DB, etc. Have integrated Data Warehouse and Business Intelligence (DW/BI) systems to put information to strategic use. Require high performance, low meantime-between-failures (MTBF), high security, high maintainability, perfect scalability, and low latency.
- 3. Why/What is cloud-deployment? Computing—data processing, storing, and networking—has become a utility such as electricity, gas, or water that can be switched on or off as required. Collocating computing resources betters economy of scale and utilization of energy, helping a greener planet. Infra as a Service (IaaS) provides only infrastructure or the metal and maximizes freedom to choose platforms or software. In addition to the above, Platform as a Service (PaaS) also provides a platform such as Windows 2012, allowing freedom to select software that is compatible with such platform; hence, providing reasonable flexibility. Often, are Virtual Machines (VM) that use the hypervisor to host selected platforms. Such VMs may, optionally, be managed—scaled and secured—by the cloud-provider. A variation—Container as a Service (CaaS)—is a soft-VM cf. Docker, which is, generally, managed by the provider. In addition to the above, Software as a Service (SaaS) also provides a programming environment that may be limited. A type of SaaS, Function as a Service (FaaS) provides standalone functions facilitating microservices. FaaS is often fortified with requisite patterns e.g., Façade, Service Registry, and Fail Fast.
- 4. What is the Optimum Denomination of Microservices? Some talk about microservices as entities. Microservices as classes or components (when contained) provide easy conceptual migration from Object-Oriented Analysis and Design (OOAD). However, classes provide only a static view—insufficient to represent—of a System under Development (SuD). Rather, an SuD is described by what it does: its APIs. Some other conceive micro services as a method or function—like a one- method API. The functional decomposition of the system could be a way to denominate microservices. The atomicity of microservices may encourage reusability through generality. A do-something business service may be broken down into microservices such as form-filling, form-saving, and form-submitting that can be reused for do-something-else business service.
- 5. What are Best Practices with Microservices? Microservices being individually maintained and versioned should be indirected through a registry. The business services’ clients need not know which microservices need be called to fulfill their requirements. An instrumentality should check health of microservices periodically: if a microservice has failed, it should fail fast the business services that use it. The ‘talkative’ REST protocol may cause avoidable strain on computing resources: consider HATEOS.
- 6. What/Why is Service Registry Business services would refer to the registry, instead of a particular microservice. Anew version of a microservice needs to be registered (or the previous version rolled back, in case of a failure) without making any change in the business processes that use them. Netflix ‘Eureka’ provides a ready-to-use implementation of Service Registry via Spring Cloud.
- 7. What/Why is Façade? The Gang of Four pattern Façade is known as API Gateway in microservices parlance. It decouples clients from the microservices by providing a business service abstraction layer in-between. Amazon Web Service has API Gateway. So has Netflix Zuul, NGiNX, Spring Cloud Gateway, etc. The link to a comparative study can be found here.
- 8. What/Why Fail Fast? Sometimes, a microservice may fail or become slow—any calls to the corresponding business services would be wasteful. A periodic health-check of microservices should be instituted. If a microservice passes the health-check, it is deemed to be working normally; otherwise abnormally. For all abnormal microservices, all dependent business services should fail fast. They should be failed by the façade, without the façade calling any of the microservices corresponding to the business service that associates a failed microservice. If the client has a stub of the façade, it may not even make a request to the façade in the first place. Refer to Spring Cloud Circuit Breaker. Normal Abnormal Performing health-check States (boxes)/Transitions (arrows)
- 9. Why Microservices Should Not Use Talkative REST?
- 10. What is Talkative REST? Is a protocol that returns everything, often unnecessary. The SOAP is bounded by the WSDL, whereas REST isn’t. A REST call may beget data that is not required. Or, not required immediately. Puts unnecessary demand on computing resources. Network bandwidth. Processor. Memory. A way to get data on demand could be useful. Cf. lazy loading. Especially suitable for microservices that aims for resource-optimization.
- 11. What is Hypermedia as the Engine of Application State (HATEOS)? Works only with matching data repositories/entity objects. Such repositories are used in a REST object to create hyperlinks to other REST objects. Much like how HTTP uses links within a document to refer to other documents. Thus, a complex object can be loaded progressively and as required. Works best if such objects are designed hierarchically. Optimizes use of computational resources—a great way to improve performance of enterprise applications. HATEOS is built atop the REST protocol. Spring Boot can easily be integrated with HATEOS