To be Reviewed By: 13 Mar 2020

Authors: Udo Kohlmeyer

Status: Draft聽| Discussion | Active | Dropped | Superseded

Superseded by: N/A

Related:聽Geode Modularization - An approach,聽Proposal for Geode Modularization,聽How to stop dependency leakage in 10 steps.pdf

Apache Geode uses many libraries and frameworks to complete features. These libraries will be on the classpath for global access within the JVM using a global Java ClassLoader (default behavior). Apache Geode has the ability to run custom code deployed onto the server-side. This means that logic that requires data can be run where the data is located, which results in potentially faster response times, as there are fewer network hops and serialization steps required to complete a single operation. Writing custom code allows users to tailor-make their logic to solve their problems. This code can use either the libraries that Apache Geode has available on its classpath OR deploy the libraries that the code requires to complete the functionality. In the latter scenario, it is possible that the custom deployed code requires/uses libraries that are conflicting in version or implementation with the libraries that Apache Geode uses. A prime example of this is Apache Geode Management's use of the Spring Framework.

In older versions of Apache Geode, the bundled Spring Framework version was on v4.3.x. Which meant that any user that wanted to use Spring in their custom code would be restricted to using that version. Manually upgrading the Spring Framework version higher, like v5.x, could result in version conflicts in either the custom deployed code, Apache Geode, or in both. In all cases, this is undesirable behavior.

Without a solution that does not restrict users on framework and versions, it will be impossible for users to most effectively use Apache Geode to their advantage. It also adds an extra burden on the Apache Geode system to always be up-to-date with all the latest versions of libraries, but also have tested with many different combinations of library versions. This of course is an impossible feat, which would result in always being on the wrong version compared to what the custom code required. i.e Apache Geode has upgraded to the latest version of libraryA (v2.0) but the custom deployed code is reliant on (v1.0) OR vice versa. One cannot keep everybody happy!!!聽

What is required is the ability to deploy custom code, that functions as expected (and tested externally) and that does not affect the Apache Geode core system or break in an unexpected manner due to version conflicts. The ability to deploy custom code with the freedom to use whatever libraries/frameworks and versions of those without any restriction. The expected behavior should be similar to a Web Container or Application Container, where the web/application does not affect the container system and is not affected by the libraries that the container system uses.

This proposal is aimed at ONLY solving/resolving problems that one is faced with when deploying custom code, into Apache Geode, and using any library/framework or version that one chooses without affecting the core Apache Geode system or without being affected by the libraries/framework that Apache Geode uses.

This proposal is not there to help define how to modularize one's code (as per the related reading) or any other approaches (like API/SPI) to simplify code and implementation.

As per the "related" content聽How to stop dependency leakage in 10 steps.pdf, the proposal hinges on the聽JBoss Modules library. This library will enable the capability to deploy modular code into Apache Geode and not affect or be affected by the libraries used by Apache Geode.

With聽JBoss Modules聽the following features are possible:

In order to have Apache Geode bootstrap correctly, Apache Geode's current bootstrapping cycle needs to be altered to accommodate this modular loading system. In order to bootstrap the "JBoss Modules" modular environment correctly, the initiating class needs to change from org.apache.geode.distributed.ServerLauncher or org.apache.geode.distributed.LocatorLauncher to using org.jboss.modules.Main. The ServerLauncher or LocatorLauncher will still be invoked, as the JBoss Modules Main is a passthrough for the command. e.g The new bootstrapping mechanism will bootstrap Apache Geode components using JBoss Modules modular system,聽which will load the Apache Geode system into its own ClassLoader.

聽 聽

The initial bootstrapping implementation is "simple".聽

There will be two bootstrapping options:

The determination of the bootstrapping type will be done in聽GFSH using an "--enable-classloader-isolation" flag. This flag will instruct GFSH to either use the current class loading mechanism or use the class loader isolated mechanism.

The biggest change that will be visible will be when opting into using the聽JBoss Modules class loading. The initial targeted implementation would be the `gfsh deploy jar' .聽

The deploy function initiated by running `deploy --jar` from聽gfsh will trigger the聽JarDeploymentService to register the module with the聽DeploymentService聽using the uploaded JAR file. This is done by the JAR file being placed in a known location on disk.聽

The聽DeploymentService聽will create a JBoss Module module, with the jar as a resource and a dependency on the Apache Geode system. The聽DeploymentService will then interact with the聽GeodeModuleLoader to load the jar into its own module and Classloader.

The deployed custom code will still have access to Apache Geode's public APIs, but not its libraries.

No anticipated performance impact.

No backward compatibility impact.

No public APIs being changed

Deploying of jars might have a small change in behavior. The initial implementation might require the user to deploy a fully built jar, not part-jars where the sum of the jars make up a whole. Upgrading of libraries will result in the old jar being undeployed and the new one deployed in its place.

An alternative to this solution is to either leave the ClassLoader model as it is currently working in Geode. Whilst the current approach has a notion of ClassLoader isolation, the user will still be limited to the versions of the libraries that Apache Geode chooses to use.

Answers to questions you鈥檝e commonly been asked after requesting comments for this proposal.

What are minor adjustments that had to be made to the proposal since it was approved?