Implementing Kubernetes operators in Java with Micronaut

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Implementing Kubernetes operators in Java with the Micronaut® framework Álvaro Sánchez-Mariscal Principal Member of Technical Staff Oracle @alvaro_sanchez

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Álvaro Sánchez-Mariscal Principal Member of Technical Staff, Oracle • Coming from Madrid • Developer since 2001 (Java stack) • Micronaut core developer since its inception (2017). • Author: Maven Plugin, Object Storage, Kubernetes, Cache, Control Panel. • Others: Core, Gradle, AWS, GCP, Azure, Security, Test, etc. • Currently at Oracle Labs: • Micronaut and Graal Development Kit for Micronaut (GDK). • GraalVM Native Build Tools. • Speaker at conferences: Devoxx, GeeCON, JavaLand, JavaZone, jPrime, Codemotion, Commit Conf, etc. @alvaro_sanchez

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Copyright © 2024, Oracle and/or its affiliates. Micronaut® is a registered trademark of Object Computing, Inc. Use is for referential purposes and does not imply any endorsement or affiliation with any third-party product. 5

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Introduction to Micronaut Copyright © 2024, Oracle and/or its affiliates 6 Micronaut is a complete solution for any type of application: microservices, message-driven producers or consumers, command-line apps, serverless functions, etc. All application types Micronaut leverages Java annotation processors and other optimisations to compute the framework infrastructure at compile-time, drastically reducing startup time and memory consumption. Highly optimised Modern, open-source Java Framework Micronaut has been designed from scratch in 2017, focused on modern architectures like microservices and serverless, and with the cloud in mind.

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Micronaut computes at build time: • All dependency and configuration injection. • Annotation metadata (meta annotations) • AOP proxies. • Bean introspections. • All other framework infrastructure. At runtime: • No reflection. • No proxy generation. • No dynamic classloading. • No classpath scanning. AOT: Ahead Of Time Copyright © 2024, Oracle and/or its affiliates 7 Source code @Singleton class MySvc {} Bytecode class $MySvc$Definition {} class $MySvc$Definition$Reference {} Source code @Builder record Person() {} Source code @Generated class PersonBuilder() {} compilation compilation

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Micronaut features: message-driven applications Kafka • Producers. • Consumers. • Kafka Streams. RabbitMQ • Producers. • Consumers. • RPC. MQTT • Publishers. • Subscribers. NATS • Producers. • Consumers. Copyright © 2024, Oracle and/or its affiliates 11

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Micronaut features: data access 13 Copyright © 2024, Oracle and/or its affiliates Interface implemented at compile time Query generated from the method name, compile-time validated Can have custom queries, inserts, etc

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Micronaut features: security 1. Authentication providers. • Bult-in support for LDAP and OAuth 2.0 password grant flow. 2. Security rules. • Configuration or annotation-based. 3. Authorization strategies. • Basic auth, session, JWT (JWKS, JWS), X.509. 4. OAuth 2.0. • Authorization code, client credentials and password grants. • OpenID Connect. • Ease of integration with providers such as Okta, Auth0, AWS Cognito, Keycloak and more. 14 Copyright © 2024, Oracle and/or its affiliates

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Micronaut features: Test Resources 1. Automatic provisioning of external resources needed during development or testing. • Containers, binaries, etc. 2. Built-in support: 3. Integrated with JUnit Platform (JUnit / Spock / Kotest) for zero-configuration Testcontainers. 15 Copyright © 2024, Oracle and/or its affiliates • MariaDB • MySQL • Oracle • PostgreSQL • SQL Server • Elasticsearch • Redis • MongoDB • Neo4j • Hashicorp Vault • Kafka • RabbitMQ • MQTT • Localstack

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Micronaut features: Serialization 1. Drop-in replacement for Jackson Databind, compile-time and reflection free. 2. Supports (most of) Jackson, JSON-B and BSON annotations. 3. Why? • Memory performance: 10x smaller runtime footprint. • Security: serializable classes must be opt-in. • Type-safety: Micronaut Serialization performs checks at compile-time (vs Jackson runtime exceptions). • Runtime portability: Micronaut Serialization at runtime supports different annotation sets. 16 Copyright © 2024, Oracle and/or its affiliates

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Micronaut features: misc 1. Dependency injection. • Can use JSR-330 (@Inject) or Spring (@Autowired) annotations. 2. Configuration. • Properties, YAML, TOML, Groovy, Config4K. 3. Validation support. • Built-in: reflection free, faster startup, smaller JAR, reduced memory. • Hibernate Validation: full Jakarta Validation API compliance. 4. AOP: Aspect-Oriented Programming. • Compile-time, reflection free. 17 Copyright © 2024, Oracle and/or its affiliates

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Micronaut features: misc 1. Distributed Tracing. • Zipkin, Jaegger. 2. Service Discovery and Distributed Configuration. • Consul, Eureka, Kubernetes. 3. Monitoring. • Micrometer, JMX, Elasticsearch. 4. API development. • GraphQL, GRPC, Open API. 5. Containers. • Docker, Kubernetes, Testcontainers. 6. Cache. • Jcache, Redis, Ehcache, Hazelcast, Infinispan, Oracle Coherence. 7. Email. 8. Error handling. 18 Copyright © 2024, Oracle and/or its affiliates

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Micronaut 4: what’s new 1. Java 17 required. • Virtual threads support (Project Loom). • @Client implementation based on java.net.http.HttpClient (JEP 321) • For older versions of Java use Micronaut 3.x. • Other languages • Kotlin 1.8, KSP support. • Apache Groovy 4. 2. GraalVM improvements. • Reachability metadata enabled. • Improved build times and reduced memory consumption. 3. Micronaut Data v4 • Hibernate 6. 24 Copyright © 2024, Oracle and/or its affiliates

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Micronaut 4: what’s new 3. Smaller, lighter runtime. • Performance closer to raw Netty (~200ms startup). • Some modules spun off core: Service Discovery, Retry, Session, Validation, Websocket. • Some dependencies now optional: Jackson, SnakeYAML, Caffeine. 4. Other features: • HTTP client/server filter methods: annotation-based and without reactive APIs. • Annotation-based CORS configuration. • HTTP/3 support. • Prefer Micronaut Serialization over Jackson. • Disabled cloud environment deduction by default. 25 Copyright © 2024, Oracle and/or its affiliates

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Service discovery 1. Allows Micronaut HTTP clients to discover Kubernetes services (kind: Service) 2. Micronaut will query the Kubernetes API to fetch the list of services and watch for changes. • By default, will search in the current namespace, but can be configured to look in different ones. • If the service is a Multi-port one, the client can be configured to use one specific port. • Available services can be filtered by using includes/excludes lists or labels. 3. Service discovery modes: • Endpoint (default): reads from kind: Endpoints objects to compute a list of instances that are load balanced by the Micronaut HTTP client. • Service: uses the ClusterIP from the service. Load balancing is handled by Kubernetes’ kube-proxy. 33 Copyright © 2024, Oracle and/or its affiliates

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Distributed configuration 1. Reads Kubernetes kind: ConfigMap and kind: Secret, and makes them available as PropertySource’s 2. Micronaut will query the Kubernetes API to fetch the list of config maps / secrets, and watch for changes. • By default, will search in the current namespace, but can be configured to look in different ones. • Available objects can be filtered by using includes/excludes lists or labels. 3. Config maps / secrets can also be read from mounted volumes (no Kubernetes API). 35 Copyright © 2024, Oracle and/or its affiliates

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Health checks 36 Copyright © 2024, Oracle and/or its affiliates 1. Probes communication with the Kubernetes API. 2. Provides some additional information about the pod where the application is running from. 3. Lists all the services discovered and their resolved URL endpoints.

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Kubernetes Java Client 1. Allows you to use dependency injection to get a ready-to-use client object from the Official Kubernetes Java client library. 2. Supports multiple authentication options. It works out-of-the-box. Can be programmatically customised. 3. Micronaut implements reactive variants with Reactor or RxJava 2/3. 4. The underlying HTTP client can be programmatically customised if needed. 38 Copyright © 2024, Oracle and/or its affiliates

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Kubernetes Operator support 1. Micronaut allows you to implement the following Kubernetes operators building blocks: • Informers. • Reconcilers. • Leader election. 2. Allows you to work with both core and custom resource definitions (CRD). 39 Copyright © 2024, Oracle and/or its affiliates

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Graal A full stack for the development and deployment of high performance Java cloud native applications

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What is Graal Development Kit for Micronaut? Copyright © 2024, Oracle and/or its affiliates 44 BUILT FOR GRAALVM NATIVE IMAGE Easily compile ahead-of-time with GraalVM Native Image into small executables that start instantly, and use less memory/CPU. CLOUD-AGNOSTIC MODULES A curated set of Micronaut modules that provide platform-independent support for core cloud services – object store, secrets, streaming, and more. DEV TOOLS AND VS CODE EXTENSIONS Dev tools to generate multicloud application starter templates. VS Code extensions for local development and cloud deployment.

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Micronaut and GraalVM 6ms As low as startup time 18MB Consuming memory footprint >30% Increased throughput up to and reduced latency

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Micronaut and GraalVM 1. The best integration possibly, supported by teams working together at Oracle Labs. • GraalVM EE includes optimisations for Micronaut for increased performance and throughput. • GraalVM EE license included in Oracle Cloud. 2. Micronaut is ready for GraalVM Native Image since day 1. • No reflection, no runtime proxies, no bytecode generation, no dynamic classloading. 3. GraalVM tooling for Visual Studio Code and Intellij IDEA. 52 Copyright © 2024, Oracle and/or its affiliates

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GraalVM Reachability Metadata Repository Community-driven collection of GraalVM reachability metadata for open-source libraries. • Actively maintained by a collective effort of VMware, Oracle and others. • Enabled in GraalVM Native Build Tools (Maven and Gradle plugins). • Integrated by default in Spring Boot and Micronaut. 53 Copyright © 2024, Oracle and/or its affiliates

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Micronaut and GraalVM powering Disney+ 57 Copyright © 2024, Oracle and/or its affiliates https://aws.amazon.com/blogs/opensource/improving-developer-productivity-at-disney-with-serverless-and-open-source/

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ABCDB: A Better Cool DataBase 1. Simple Micronaut application that pretends being a database product. 2. We want our customers to install it with a Kubernetes operator. • Instances will be created with a Custom Resource Definition 3. Packaged as a native executable inside a Docker image. 4. Can read configuration from a ConfigMap, and has a @Refreshable endpoint. 59 Copyright © 2024, Oracle and/or its affiliates