Quarkus

Quarkus  is a Java framework tailored for deployment on Kubernetes. Key technology components surrounding it are OpenJDK HotSpot and GraalVM. The goal of Quarkus is to make Java a leading platform in Kubernetes and serverless environments while offering developers a unified reactive and imperative programming model to optimally address a wider range of distributed application architectures.

Version history
Quarkus offers quick scale-up and high-density utilization in container orchestration platforms such as Kubernetes. Many more application instances can be run given the same hardware resources. After its initial debut, Quarkus underwent several enhancements over the next few months, culminating in a 1.0.0 release within the open-source community in November 2019.

GraalVM Community Edition (CE) & GraalVM Enterprise Edition (EE)
GraalVM is a Java Virtual Machine for compiling and running applications written in different languages to a native machine binary. GraalVM Community Edition has varying support and licensing requirements.

Mandrel
Mandrel is a downstream distribution of GraalVM CE, supporting the same capabilities to build native executables but based on the open source OpenJDK. Mandrel aims to make GraalVM easy to consume by Quarkus applications by only including GraalVM CE components that Quarkus needs. Red Hat began commercial support for using Mandrel to build native Quarkus applications since the Quarkus 1.7 release in October 2020.

Container first
From the beginning, Quarkus was designed around the container-first and Kubernetes-native philosophy, optimizing for low memory usage and fast startup times.

As much processing as possible is done at build time, including taking a closed-world assumption approach to building and running applications. This optimization means that, in most cases, all code that does not have an execution path at runtime isn't loaded into the JVM.

In Quarkus, classes used only at application startup are invoked at build time and not loaded into the runtime JVM. Quarkus also avoids reflection as much as possible, instead favoring static class binding. These design principles reduce the size, and ultimately the memory footprint, of the application running on the JVM while also enabling Quarkus to be natively-native.

Quarkus' design accounted for native compilation from the onset. It was optimized for using the native image capability of GraalVM to compile JVM bytecode to a native machine binary. GraalVM aggressively removes any unreachable code found within the application's source code as well as any of its dependencies. Combined with Linux containers and Kubernetes, a Quarkus application runs as a native Linux executable, eliminating the JVM. A Quarkus native executable starts much faster and uses far less memory than a traditional JVM.


 * Fast Startup (tens of milliseconds) allows automatic scaling up and down of microservices on containers and Kubernetes as well as FaaS on-the-spot execution
 * Low memory utilization helps optimize container density in microservices architecture deployments requiring multiple containers
 * Smaller application and container image footprint

Live coding
One of the major productivity problems that most Java developers face is traditional Java development workflow. For most web developers this will generally be:

Write Code → Compile → Deploy → Refresh Browser → Repeat

This can be a major drain on productivity, as the compile + redeploy cycle can often take up to a minute or more. Quarkus aims to solve this problem with its Live Coding feature. When running in development mode the workflow is simply:

Write Code → Refresh Browser → Repeat

This will work out of the box, with no special setup required. This works for application source files, configurations, and static resources.

Interactive developer user interface (DEV UI)
Quarkus provides an interactive developer UI to showcase all added dependencies when a developer accesses the  endpoint after the Quarkus dev mode gets started via   command-line. The developers also can update configurations then the changes will sync the application.properties file up automatically.

Zero configuration with DevServices
Installing a database in a developer's local environment is not a trivial task if the database should be the same as the production version. Linux users (developers) can run the database easily using a container command-line tool and a container engine. They still tend not to run production-ready databases (e.g., PostgreSQL and MariaDB) due to the high consumption of the computer's resources. Instead, they prefer to use in-memory datastores like the H2 database.

Quarkus provides the DevServices built on test containers to solve this problem. For example, a developer can do test applications if they work in the production database, PostgreSQL rather than H2 in-memory datastore in the application.properties file:

DevServices is generally enabled by default unless there is an existing configuration present. When DevServices is enabled Quarkus will attempt to automatically configure and start a database when running in development or test mode.

Continuous testing
Not testing is not an option to develop robust applications in software development from monolithic application to microservices. Developers probably think of external continuous integration (CI) tools that a QA team most likely has responsibility for verifying test cases.

What if the developers do not need to integrate the CI tools but perform the test cases on a runtime environment where business applications are developing and running?

Quarkus provides a continuous testing feature through the command-line interface as well as the DEV UI. This feature removes the developer's efforts to integrate an external CI tool and ensures functionality while continuously developing business logic.

Built on standards
Quarkus rests on a vast ecosystem of technologies, standards, libraries, and APIs. Developers do not have to spend lots of time learning an entirely new set of APIs and technologies to take advantage of the benefits Quarkus brings to the JVM or native images. Among the specifications and technologies underlying Quarkus are Contexts & Dependency Injection (CDI), JAX-RS, Java Persistence API (JPA), Java Transaction API (JTA), Apache Camel, and Hibernate, just to name a few.

Quarkus is an Ahead-of-Time compilation (AOT) platform, optimizing code for the JVM as well as compiling to native code for improved performance. All of the underlying technologies are AOT-enabled, and Quarkus is continually incorporating new AOT-enabled technologies, standards, and libraries.