This document discusses characteristics of enterprise applications and microservices architecture. It describes how enterprise applications have large user bases, store data across various databases, and require high performance. Microservices break applications into smaller, independent pieces that use service registries and APIs to communicate. The document recommends microservices be defined by their APIs and functional decomposition. It also provides best practices like using service registries, facade patterns, and failing fast on abnormal 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