Native Cloud-Native: Building Agile Microservices with the Micronaut Framework

© 2023 Object Computing, Inc. All rights reserved. No part of these notes may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means,
electronic, mechanical, photocopying, recording, or otherwise, without the prior, written permission of Object Computing, Inc.
Natively Cloud Native
Building Agile Microservices with the
Micronaut Framework™

Copyright © 2023 by Object Computing, Inc. (OCI).
All rights reserved.
About Me
Zachary Klein
• Principal Software Engineer,
Object Computing
• Speaker/instructor
• OSS Contributor to Grails &
Micronaut frameworks
@ZacharyAKlein
kleinz@objectcomputing.com
2

A modern, JVM-based, full-stack framework for building modular,
easily testable microservice and serverless applications.

History of Micronaut
4
• Micronaut announced in March 2018
• Framework open-sourced in May 2018, 1.0 release in
October 2018
• Triggered a wave of excitement and innovation
around the JVM - Quarkus, Spring Fu, etc
• Micronaut 3.0 released in August 2021 - Micronaut
4.0 expected in Q2
• Micronaut continues to point the path forwards for
server-side Java frameworks

Goals of Micronaut
5
• Designed With Microservices In Mind
• Fast Startup Time - No reflection
• Low Memory Footprint - No reflection
• Small Executable Jar Files
• AOT Compilation - Minimal runtime dependencies

Introduction To The
Micronaut Framework
• A framework for microservice & serverless apps
• Leverages Ahead Of Time (AOT) compilation:
• DI, AOP, code introspection
• Reactive HTTP layer built on Netty: https://netty.io
• Declarative HTTP Client
• Collection of framework integrations and libraries
• Build-tool agnostic (Maven & Gradle plugins
provided)
• Natively Cloud Native
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Natively Cloud Native
7
• Service Discovery
• Consul, Eureka, K8s…
• Distributed Configuration
• AWS, GCP, K8s, etc…
• Client-Side Load Balancing
• Serverless Computing
• AWS Lambda, Azure, GCF, etc
• Distributed Tracing
• Token propagation… and more!

What Can You Build With
The Micronaut Framework?
• Microservices
• Serverless Applications
• Message-Driven Applications with
Kafka/RabbitMQ
• CLI Applications
• Android Applications
• Anything with static void
main(String..args)
8

Why Should I Care About
Micronaut?
• Java and Traditional Java frameworks were not
designed with microservices & serverless in mind
• JVM-based DI/AOP solutions make heavy use of
reflection, runtime caches, and proxies
• Not optimized for fast cold starts (severless) or low
memory usage (microservices/containers)
9

Ahead of Time Compilation
Generated Bytecode
resides in the same
package as your
source code - your
code is never
altered by Micronaut

GraalVM
• "A high-performance JDK designed to accelerate
Java application performance while consuming fewer
resources”
• Allows generation of light-weight native images
• Minimal support for reflection
• Micronaut is officially “Ready for Native Image”
(tested by framework maintainers)

GraalVM

What is a Micronaut App?
• Micronaut-Inject: Core DI, AOP
• Micronaut-Runtime: ApplicationContext,
configuration
• HTTP-Server & Client: Reactive HTTP layer*
• A suite of configurations & libraries providing
advanced features (security, data access, messaging,
etc)
* Servlet containers are supported: https://micronaut-
projects.github.io/micronaut-servlet/1.0.2/guide/
index.html
14

configuration
etc)
Can be used in any JVM-based
application!
15

configuration
etc)
Included in a standard Micronaut
Application (via CLI or Launch)
16
Plus your choice of build tool:

configuration
etc)
Added to your project manually OR
specified as “features” when creating
the app via CLI or Launch
17

Creating a Micronaut App
• Micronaut Launch: https://
launch.micronaut.io
• SDKMan: https://sdkman.io
• Homebrew/MacPorts
• Binary or Source: https://
micronaut.io/download.html

Copyright © 2023 by Object Computing, Inc.
Non-blocking HTTP Server

URI Templates
/books/{id} Simple match
Integer id
/books/1
/books/{id:2} A variable of 2 characters max
Integer id
/books/10
/books{/id} An optional URI variable
@Nullable Integer id
/books/10 or /books
/book{/id:[a-zA-Z]+} An optional URI variable with regex
@Nullable String id
/books/foo
/books{?max,offset} Optional query parameters
@Nullable Integer max
/books?max=10&offset=10
/books{/path:.*}{.ext} Regex path match with extension
@Nullable String path
/books/foo/bar.xml
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Reactive Controllers
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Declarative HTTP Clients

Micronaut HTTP Client
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❖Netty-Based HTTP Client
❖Low-level API and declarative
compile-time client
❖Uses @Introduction advice to
simplify writing clients
❖Reactive, CompletableFuture
and blocking I/O support
❖Built-in Service Discovery support
❖Support for multi-part uploads,
streaming data over HTTP, etc

27

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https://guides.micronaut.io/latest/tag-json-streams.html

Fast & Easy Testing

© 2023 Object Computing, Inc. (OCI) All rights reserved. No part of these notes may be reproduced, stored in a retrieval system, or transmitted, in any form or by any
means, electronic, mechanical, photocopying, recording, or otherwise, without the prior, written permission of Object Computing, Inc. (OCI)
DEPENDENCY INJECTION

Dependency Injection
❖Micronaut Contains A Full Featured Dependency
Injection (DI) Container
❖Uses jakarta.inject.* Annotations
❖JSR-330 Compliant
‣ Passes The Full TCK
❖Supports Constructor Injection As Well As
Property And Field Injection
‣ insert heated debate here…
31

Field Injection
import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Get;
import javax.inject.Inject;
@Controller("/")
public class HelloController {
@Inject
// Could be private, protected,
// package-protected or public
private MessageHelper messageHelper;
// ...
}
33

Constructor Injection
import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Get;
@Controller("/")
public class HelloController {
private final MessageHelper messageHelper;
public HelloController(MessageHelper messageHelper) {
this.messageHelper = messageHelper;
}
// ...
}
RECOMMENDED! 34

Conditional Beans
❖Bean Definitions May Be Marked With @Requires
To Conditionally Load Them
❖Examples:
@Requires(classes = org.hibernate.classic.Lifecycle.class)
@Requires(property = “some.property")
@Requires(property = “some.property”, value = "some value")
@Requires(beans = javax.sql.DataSource.class)
@Requires(env = "test")
@Requires(notEnv = "test")
@Requires(sdk = Requires.Sdk.JAVA, version = “1.8")
35

Replaceable Beans
❖ @Replaces May Be Used In Conjunction With
@Requires To Optionally Replace Beans
@Singleton
@Requires(beans = DataSource.class)
public class JdbcBookService implements BookService {
// Real BookService Impl...
}
@Singleton
@Requires(env = Environment.TEST)
@Replaces(JdbcBookService.class)
public class MockBookService implements BookService {
// Mock BookService Impl...
}
36

PostConstruct
@Refreshable
public static class WeatherService {
private String forecast;
@PostConstruct
public void init() {
forecast = "Scattered Clouds "
+ new SimpleDateFormat("dd/MMM/yy HH:mm:ss.SSS”)
.format(new Date());
}
public String latestForecast() {
return forecast;
}
}
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PreDestroy
import javax.annotation.PreDestroy;
import jakarta.inject.Singleton;
import java.util.concurrent.atomic.AtomicBoolean;
@Singleton
public class PreDestroyBean implements AutoCloseable {
AtomicBoolean stopped = new AtomicBoolean(false);
@PreDestroy
@Override
public void close() throws Exception {
stopped.compareAndSet(false, true);
}
}
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Application Configuration
39

Config Files
❖Micronaut Supports Multiple Formats
❖Defined In src/main/resources/
‣ application.properties
‣ application.yml
‣ application.groovy
‣ application.json
❖Environment specific configuration with -suffix:
‣ application-test.yml
‣ application-gcp.yml
https://docs.micronaut.io/latest/api/io/micronaut/context/env/Environment.html
40

Config Files
41

Injecting Config Values
❖Config Values May Be Injected Into Property
References Using @Value(…)
import io.micronaut.context.annotation.Value;
@Controller
public class SomeController {
@Value("${some.config.value}")
protected String someProperty;
// ...
}
42

Random Config Properties
❖Micronaut provides a set of randomly assigned
properties that you can use within your config
Property Value
random.port An available random port number
random.int Random int
random.integer Random int
random.long Random long
random.float Random float
random.shortuuid Random UUID of only 10 chars in length
random.uuid Random UUID with dashes
random.uuid2 Random UUID without dashes
micronaut:
application:
name: myapplication
instance:
id: ${random.shortuuid}
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Alternate Config Sources
❖SPRING_APPLICATION_JSON
❖MICRONAUT_APPLICATION_JSON
❖System Properties
❖OS Environment Variables
❖Cloud Configuration
❖application-[env].[extension]
‣ env = runtime environment
44

Configuration Annotations
❖ io.micronaut.context.annotation.ConfigurationProperties
❖ io.micronaut.context.annotation.EachProperty
❖ io.micronaut.context.annotation.EachBean
45

Management Endpoints
❖Micronaut Provides A Set Of Management
Endpoints
❖Requires A Dependency On The management
Library
‣ "io.micronaut:micronaut-management"
❖Applications May Contribute Custom Endpoints
As Beans
46

47

/beans Returns information about the loaded bean
definitions in the application
/info Returns static information from the state of the
application
/health Returns information about the "health" of the
application
/metrics Return the application metrics. Requires the
micrometer-core configuration on the classpath
/refresh Refreshes bean state
/routes Returns information about URIs available to be
called for your application
/stop Shuts down the application server (disabled by
default)
/loggers View and mutate logging configuration (e.g, POST to
change log levels at runtime)
/env Returns all currently resolved configuration
properties
48

Micronaut Service Discovery
❖Support for Consul, Kubernetes and Eureka
❖Configuration Support for Consul, Kubernetes,
Vault, Spring Cloud Config Server and AWS
ParameterStore
❖Native Client-Side Load-Balancing
implementation ‘io.micronaut:micronaut-discovery-client'
49

Micronaut Service Discovery
micronaut:
application:
name: service-a
consul:
client:
registration:
enabled: true
defaultZone: "${CONSUL_HOST:localhost}:${CONSUL_PORT:8500}"
$ docker run -p 8500:8500 consul:1.2.4
src/main/resources/application.yml
Start up Consul with Docker
50

Cacheable
❖Annotate classes and methods to specify caching
behavior
51
@Singleton
@CacheConfig("headlines")
public class NewsService {
@Cacheable
public List<String> headlines(Month month) {
//This method is cacheable
}
@CachePut(parameters = {"month"})
public List<String> addHeadline(Month month, String headline) {
//Return value is cached with name headlines for the supplied month.
}
@CacheInvalidate(parameters = {"month"})
public void removeHeadline(Month month, String headline) {
//invalidates the cache headlines for the supplied month.
}
}

Scheduled
❖Annotation for scheduling background tasks (can
also be done programmatically via TaskScheduler)
52
@Scheduled(fixedDelay = "5m")
void fiveMinutesAfterLastExecution() {
System.out.println("Executing fiveMinutesAfterLastExecution()")
}
@Scheduled(cron = "0 15 10 ? * MON" )
void everyMondayAtTenFifteenAm() {
System.out.println("Executing everyMondayAtTenFifteenAm()")
}
@Scheduled(initialDelay = "1m" )
void onceOneMinuteAfterStartup() {
System.out.println("Executing onceOneMinuteAfterStartup()")
}

Retryable
❖Indicates that the method call should be re-
attempted for a configurable number of times,
before throwing an exception
53
@Retryable(
attempts = “5",

delay = “2s"
)
public Book findBook(String title) { //...
@Retryable(attempts = "${book.retry.attempts:3}",

delay = "${book.retry.delay:1s}" )

Circuit Breaker
❖Variation of @Retryable which (after a set number
of failures) will immediately re-throw the exception
without waiting for the method to fail
54
@CircuitBreaker(
attempts = “5",

delay = “2s”

reset = “30s”
)
public Book findBook(String title) { //...

Distributed Tracing
Catalog Inventory
Storefront
55

Distributed Tracing
@NewSpan("productList")
List<Product> productList() {
//Get products
}
@ContinueSpan
@Get(“/{id}”)
HttpResponse<Product> show(Long id) {
//Get product
}
@Get("/{productNumber}")
HttpResponse<Integer> hits(
@SpanTag("product") String product
) {}
❖ @NewSpan begins a
new tracing segment
at this method
❖ @ContinueSpan
includes this method
within the current
span
❖ @SpanTag allows
metadata to be
added to the (new or
current) span

Tracing UI
57

OpenAPI Documentation
58
https://dzone.com/articles/a-quick-guide-to-microservices-with-the-micronaut
micronaut:
router:
static-resources:
swagger:
paths: classpath:META-INF/swagger
mapping: /swagger/**
src/main/resources/application.yml

Micronaut Data
❖Precomputes Queries at compilation
time.
❖Solution for Static Queries
❖Uses Micronaut's reflection-free AOP.
❖Zero runtime overhead database
access solution
❖Compilation time checking
❖Smaller stack traces
59

Micronaut Data JPA
❖Support for Hibernate JPA
❖Precomputes JPA-QL queries
❖Provides a full ORM experience
❖Hibernate’s dialect support and
features
❖Con: Hibernate relies on runtime
reflection
60

Micronaut Data JDBC
❖Support for native JDBC
❖Data Mapper vs ORM
❖Focused on DTOs
❖Light-weight and reflection/
proxy-free
61
JDBC

JPA vs JDBC
62
JDBC Hibernate/JPA
More efficient Higher memory requirements
Few Dialects Greater dialect support
DTO-oriented Entity to Table
Optimized for reads Optimized for writes
Better for serverless Not optimized for cold starts
JDBC

Micronaut Data Entity
// src/main/java/demo/Car.groovy
package demo;
import io.micronaut.data.annotation.MappedEntity;
import io.micronaut.data.annotation.GeneratedValue;
import io.micronaut.data.annotation.Id;
@MappedEntity
public class Car {
@Id
@GeneratedValue
private Long id;
private String make;
private String model;
// …
}
63

Micronaut Data Repository
package demo;
import io.micronaut.data.jdbc.annotation.JdbcRepository;
import io.micronaut.data.model.query.builder.sql.Dialect;
import io.micronaut.data.repository.CrudRepository;
@JdbcRepository(dialect = Dialect.MYSQL)
public interface CarRepository extends CrudRepository<Car, Long> {}
64

Micronaut Data Repository
package demo;
import io.micronaut.data.jdbc.annotation.JdbcRepository;
import io.micronaut.data.model.query.builder.sql.Dialect;
import io.micronaut.data.repository.CrudRepository;
@JdbcRepository(dialect = Dialect.MYSQL)
public interface CarRepository extends CrudRepository<Car, Long> {
void update(@Id long id, String make, String model);
Car save(String make, String model);
List<Car> findAllByMake(String make, String model);
Integer countAllByMakeAndModel(String make, String model);
}
65

Micronaut Security
66
❖Official security solution for
Micronaut apps
❖Follows similar pattern to Spring
Security (also implements JSR
250 annotations)
❖Makes use of HTTP filters
❖Supports basic auth, session
auth, JWT & OAuth 2.0

Micronaut Kafka
• https://micronaut-projects.github.io/micronaut-kafka/
• Provides declarative API for publishing/consuming
events in Kafka
• Reflection-free serialization/deserialization of events
• Create messaging apps without a HTTP server
67

Producer
68

Consumer
69

Kafka Summit Presentation
70
https://www.confluent.io/events/kafka-summit-
europe-2021/event-driven-applications-with-kafka-
micronaut-and-aws-lambda/

Deploying to the Cloud
❖Micronaut applications can be deployed as JAR
files, containerized microservices; (optionally) as
native images
❖Cloud-Provider specific features available in
Micronaut Launch for:
‣ AWS Lambda
‣ Google Cloud Run / Functions / Compute /
AppEngine
‣ Oracle Cloud Infrastructure
‣ Microsoft Azure
71

72
❖Micronaut Guides
includes step-by-
step tutorials for
deploying to major
Cloud Platforms

https://guides.micronaut.io/latest/micronaut-google-cloud-
platform-cloud-run.html

Create the Google Cloud project (use gcloud to
authenticate and set the project ID)

gcloud auth configure-docker - sets up your local
Docker to point to Google Container Registry

Add Docker image info to build.gradle:
Push image to the Google Container Registry:

Deploy Google Cloud Run

Invoke deployed service:

Summary
❖Micronaut is a full-featured
framework designed for cloud-
native architectures
❖Offers features that are useful in
every sort of application
❖Micronaut is actively evolving - 4.0
due in Q2!
❖Micronaut community is growing
and is super helpful - join the Gitter
channel! https://app.gitter.im/#/
micronautfw
84

Resources
❖micronaut.io/launch
❖micronaut.io/docs
❖micronaut.io/guides
❖micronaut.io/blog
❖micronaut.io/foundation
❖https://app.gitter.im/#/micronautfw
85

Resources
86
https://micronautpodcast.com/

Resources
87
https://groovypodcast.podbean.com/

© 2023 Object Computing, Inc. All rights reserved. No part of these notes may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means,
electronic, mechanical, photocopying, recording, or otherwise, without the prior, written permission of Object Computing, Inc.
Thank You!
Zachary Klein - kleinz@objectcomputing.com

Native Cloud-Native: Building Agile Microservices with the Micronaut Framework

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