The document discusses microservices and the Dropwizard framework. It provides definitions of microservices, noting they should be small, autonomous services. It outlines benefits of microservices like scalability, resilience and ease of deployment. It then discusses Dropwizard, describing it as a framework for developing rapid, ops-friendly and high-performance RESTful web services. Key aspects of Dropwizard like its use of Jetty, Jersey, Jackson and other libraries are summarized. Anatomy of a basic Dropwizard application and Jersey resource are briefly explained. Finally, it touches on Dropwizard's support for operations through configurations, metrics, and testing web services.

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Microservice? For elaborate history/definition/explanation -
http://martinfowler.com/articles/microservices.html
“Small and focused on
doing one thing well”
No proper definition of small - depends on context.
According to Jon Eves from RealEstate.com.au -
something that can be re-written in 2 weeks.
Autonomous
● Might be deployed as an isolated service
on a PaaS.
● To avoid coupling - all communication
between services themselves must be via
network calls.
● Service exposes a technology agnostic
API.

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Benefits of Micro-service (as opposed to monolith)
Technology heterogeneity
Resilience
Scaling
Ease of deployment
Organizational Alignment
Composability
Optimizing for replaceability
For elaborate explanation on each of them refer to
the book “Building Microservices” by Sam Newman

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Microservice vs SOA
Problems of SOA -
● bloated vendor middleware (MoMs, ESBs)
● technology-aware communication protocols
● no apparent guidance for monolith decomposition
● RPC/RMI tend to create coupling in a way that any change in Server
requires the client to change too
Microservice approach has emerged from real-world use - taking the
developers better understanding of systems/architecture to do SOA well.
Relationship between Microservice approach to SOA is similar to what
Scrum/Sprint is to Agile software development methodology.

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Microservice Development Frameworks
Selecting a single framework defeats the purpose.
Tools should be selected based on the requirement.
Having said that, some clear choices in Java space -
● Dropwizard.io
● Karyon by Netflix
● Spring Boot

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What is Dropwizard?
http://gunshowcomic.com/316

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What is Dropwizard?
Balancing between being a
library and a framework
for developing -
● Rapid
● Ops-friendly
● high-performance
● RESTful web services

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Dropwizard Ecosystem
Jetty Library -
Http/Servlet Container
Jersey - JAX-RS
Implementation for RESTful
Webservices
Jackson - JSON Library
View Bundle
Hibernate Bundle
Freemarker/Mustache
Template
Quartz
Integration
Metrics library
Populate application
performance data
Asset Bundle
Sundial Bundle
Apache HttpClient
Guava
Joda Time
Logback/Slf4j

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What constitutes a Dropwizard Application?
MyConfiguration MyApplication (main)
*.yaml
(dev, test, prod)
dataSource:
driverClass: org.hsqldb.jdbcDriver
user: sa
password:
url: jdbc:hsqldb:file:testdb
properties:
hibernate.dialect: org.hibernate.dialect.HSQLDialect
hibernate.hbm2ddl.auto: update
.
.
logging:
level: INFO
loggers:
io.dropwizard: INFO
au.com.fairfax.media.seo: DEBUG
appenders:
- type: console
.
.
public static void main(String[] args) throws Exception {
new MyApplication().run(args);
}
public void initialize(Bootstrap<MyConfiguration> bootstrap) {
// add View bundle, Asset bundle, Hibernate bundle, etc
}
public void run(MyConfiguration conf, Environment environment) {
// initialize and register application objects
// - services, dao, resource end-points, health-checks
}
Running a fully functional autonomous microservice is as simple as -
$ java -jar <myservice.jar> server <myconfig>.yaml

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Anatomy of a Jersey Resource: RESTful Web-service Enabler
@Path("report")
public class ReportResource {
private Dao dao;
@GET
@Produces(TEXT_HTML)
public ReportView showReport() {
ReportView reportView = new ReportView();
reportView.addModel(...);
return reportView;
}
@GET
@Timed
@UnitOfWork
@Path("by-date")
@Produces(APPLICATION_JSON)
public Message<List<ArticleCount>> reportByDate(@QueryParam("date") Date date) {
List<ArticleCount> counts = dao.getList(...);
return new Message<>(Message.SUCCESSFUL, counts);
}
}
public class ReportView extends View {
private Map<String, Object> model = new HashMap<>();
public ReportView() {
super("report.ftl");
}
public void addModel(String key, Object value) {
model.put(key, value);
}
public Map<String, Object> getModel() {
return model;
}
}
http://localhost:8080/report
Collect performance metric
Ensures Transactional operation
View rendering by
Freemarker Template
http://localhost:8080/report/by-date
Alternatively, your
service end-point could
only serve JSON data,
and all view rendering
logic reside in client.

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Ops Friendly?
Easy to provide different configurations/run-modes
Built-in application metrics (such as @Timed)
Logging/Additional Health-Checks
Thread dump
Optional integration with Operational tools - Graphite,
Nagios
environment.healthChecks().register("shareCountAPI",
new SharedCountApiHealthCheck(...));
By default Dropwizard collects many
application performance data that can be
consumed from the admin port
(localhost:8081) like a web-service itself.
This makes the integration with the
external monitoring systems convenient.
Different *.yaml file for
different run-modes (test, dev,
prod)

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@RunWith(MockitoJUnitRunner.class)
public class ReportResourceTest {
private static final MyDao dao = mock(MyDao.class);
@ClassRule
public static final ResourceTestRule reportResource = ResourceTestRule.builder()
.addResource(new ReportResource(dao))
.build();
@Test
public void testReportByDateShouldReturnSuccessMessage() throws Exception {
when(dao.getList(...)).thenReturn(Arrays.asList(new ArticleCount()));
Message<> result = reportResource.client().target("/report/by-date").request().get(<expected type>);
assertEquals(Message.SUCCESSFUL, result.getStatus());
}
Testing Web-service End-points
Also, DropwizardAppRule allows starting/stopping the application within the context of a
test case to check the full life-cycle.

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Sample implementation-
https://bitbucket.org/fairfax/seo-shared-count-report
Thank You!