# Quarkus

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

## Version history

| Version | Date | Notes |
| 0.12 | March 20, 2019 | Initial release |
| 1.0 | Nov 2019 | |
| 2.0 | Jun 2021 | |
| 3.0.1 | Mar 2023 | |
| 3.2.6 | Oct 2023 | LTS (3.2) |
| 2.16.12.Final | October 17, 2023 | |
| 3.2.7.Final | October 19, 2023 | |
| 3.5.0 | October 25, 2023 | |
| 3.2.9.Final | November 17, 2023 | |
| 3.6.0 | November 29, 2023 | |
| 3.2.10.Final | Jan 2024 | |
| 3.7.1 | Jan 2024 | |
| 3.8.1 | Feb 2024 | LTS (3.8) |
| 3.10.0 | Apr 2024 | |
| 3.13.0 | July 2024 | |
| 3.15.2 | Nov 2024 | LTS (3.15) |
| 3.16.2 | Nov 2024 | |
| 3.17.7 | Jan 2025 | |
| 3.18.3 | Feb 2025 | |
Quarkus offers quick scale-up and high-density use 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.

## Distributions
### GraalVM Community Edition (CE) and 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.

## Design pillars
### 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 use 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.
| Note | When you run mvn compile quarkus:dev Quarkus will launch in development mode. When it receives a HTTP request it will hold the request, and check to see if any application source files have been changed. If they have it will transparently compile the changed files, redeploy the application with the changed files, and then the HTTP request will continue to the redeployed application. Quarkus redeploys are much faster than a traditional app server, so for all but the largest applications this should take well under a second. |

#### Interactive developer user interface (DEV UI)

Quarkus provides an interactive developer UI to showcase all added dependencies when a developer accesses the http://localhost:8080/q/dev endpoint after the Quarkus dev mode gets started via mvn quarkus:dev 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:
quarkus.datasource.devservices.image-name=postgres:latest
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.