Apereo CAS - Efficient Deployments with Class Data Sharing

Posted by Misagh Moayyed on May 26, 2024 · 8 mins read ·
Content Unavailable
Your browser is blocking content on this website. Please check your browser settings and try again.

Efficiency is a key factor that can significantly impact user experience when it comes to Spring Boot applications and that of Apereo CAS. Today, we’ll look at an Apereo CAS deployment that would be packaged and run as a Spring Boot application and explore techniques to enhance deployment efficiency and startup times. Our focus will be on packaging CAS as an executable WAR, utilizing Class Data Sharing (CDS), and leveraging Application Class-Data Sharing (AppCDS) for optimal performance, particularly for unpacked deployments.

This tutorial specifically focuses on:

  • CAS 7.1.x
  • Java 21

The Build

Apereo CAS Initializr is a component in the Apereo CAS ecosystem that allows you as the deployer to generate CAS WAR Overlay projects on the fly with just what you need to start quickly. Conceptually identical to start.spring.io, you can browse the user interface and add/remove modules that you wish to include in your deployment from the menu. At its most basic form, you can in the end either download the project as a .zip file manually or do so via the command line:

mkdir cas-server && cd cas-server
curl "https://getcas.apereo.org/starter.tgz" | tar -xzvf -

Then, it’s time to build the project:

./gradlew build

…and now it’s time to run the application. Let’s review options.

Executable WAR

The easiest way to run is to run CAS as an executable web application with embedded Apache Tomcat container:

java -jar build/libs/cas.war --server.ssl.enabled=false --server.port=8080
<Started CasWebApplication in 10.283 seconds (process running for 11.564)>

Not bad, but we can do better. It is often an advantage to explode the web application and run it in a different way. Certain PaaS implementations choose to unpack archives before they run. One way to run an unpacked archive is by starting the appropriate launcher, as follows:

jar -xf build/libs/cas.war
cd build/libs
java org.springframework.boot.loader.launch.JarLauncher
<Started CasWebApplication in 7.693 seconds (process running for 9.285)>

This is slightly faster on startup (depending on the size of the CAS WAR file) than running from an unexploded archive. After startup, you should not expect any differences. Alternatively, once you have unpacked the .war file you can also get an extra boost to startup time by running the app with its “natural” main method instead of the JarLauncher. For example:

jar -xf build/libs/cas.war
cd build/libs
java -cp "WEB-INF/classes:WEB-INF/lib/*" org.apereo.cas.web.CasWebApplication
<Started CasWebApplication in 6.873 seconds (process running for 7.469)>

Cool, eh?

Using the JarLauncher over the CasWebApplication has the added benefit of a predictable classpath order. The WAR file contains a classpath.idx file which is used by the JarLauncher when constructing the classpath.

Class Data Sharing (CDS)

Class Data Sharing (CDS) helps reduce the startup time and memory footprint of JVMs by caching class metadata in an archive file so that it can be quickly pre-loaded into a newly launched JVM. This accelerates class loading, a significant contributor to startup time. A default CDS archive is pre-packaged with most recent JDK distributions to contain metadata for common JDK classes. We can also create customized CDS archives to speed up the loading of classes in CAS.

A CDS archive for an unpacked-already CAS can be created when the application exits. The Spring Framework provides a mode of operation where the process can exit automatically once the application context has been refreshed. In this mode, all non-lazy initialized singletons have been instantiated, and callbacks have been invoked but the lifecycle has not started.

To build and run CAS with CDS, you must first make sure the CAS web application is built without executable mode:

./gradlew clean build -Pexecutable=false

Then, extract the uber WAR:

java -Djarmode=tools -jar build/libs/cas.war extract

If the WAR file is invalid, you will receive the following error:

Error: File 'cas.war' is not compatible; ensure jar file is valid and launch script is not enabled

This creates a cas/cas.war file and the needed libraries in a cas/lib folder at the root of the project directory. Then we need to perform a training run:

java -XX:ArchiveClassesAtExit=./cas/cas.jsa -Dspring.context.exit=onRefresh -jar cas/cas.war

This creates a cas.jsa file that can be reused as long as the application is not updated. Finally, CAS can then be executed with:

java -XX:SharedArchiveFile=./cas/cas.jsa -jar cas/cas.war
<Started CasWebApplication in 6.216 seconds (process running for 7.582)>

A tiny bit better. Note that CDS technology keeps getting better and better in each new JVM release. Unpackaged Spring Boot executable JARs or WARs do not yet fulfill all the conditions that are needed for optimal CDS performance and future upgrades are expected to bring more improvements to this area. Ultimately, the combination of CDS and Spring AOT optimizations should reduce the CAS startup time quite a bit.

Need Help?

If you have questions about the contents and the topic of this blog post, or if you need additional guidance and support, feel free to send us a note and ask about consulting and support services.


I hope this review was of some help to you and I am sure that both this post as well as the functionality it attempts to explain can be improved in any number of ways. Please feel free to engage and contribute as best as you can.

Happy Coding,

Misagh Moayyed