On Platforms

I’m primarily (as always) talking Java, here. This post has a larger purpose but I’m not there yet. If all goes according to plan this post will make sense with some others to follow. At the moment it probably doesn’t make much sense. If that’s your thing, read on. You may also be interested in the next post in this series.

What is a platform?

If I have one library with one class in it, with one function, do I have a platform? What about two functions? Two classes? Two libraries?

In my opinion, it depends on what it does.

Maybe I’m naïve, but I think a platform has to have a definition of what a packaged application looks like, a way to create such a packaged application (or at least verbiage about how to do it), and a way to run a packaged application that is handed to it. It may or may not also include a framework or libraries that the application may or must use.

You write and package an application to run on a platform, optionally (or not) using the platform’s facilities, and the application and the platform are distinct entities and have notionally different lifespans (that may of course nevertheless line up).

How the packaged application is expected to look and how it runs is dictated by the platform. Also, in most cases, but I suppose not all, a platform dictates how the application must look but not how it is produced.

So Docker, for example, is a platform, because, among other things, it tells you what a packaged application is, one way among several to package your application (docker build) and how to run it (docker run). Docker itself doesn’t really include any kind of framework that your application would use: your application is responsible, wholly, for doing whatever it wants to do. Here you can start to argue semantics about things like volume mounts and whatnot if you so choose, and if you do that I will start checking my phone and waiting for you to leave.

Is Kubernetes a platform? Unquestionably, it seems to me, by the same logic. (Also, anything with that many metric tons of YAML is probably a platform by fiat, or at least a ZIP code.)

Jakarta EE (and Java EE before it) is a platform because it tells you how to package your application (mvn {war plugin incantations}) such that a very specific ZIP file with a very specific filename suffix is created, or at least what an application so packaged must look like, and how to run (deploy) it. Well, hmm; no, it doesn’t really tell you how to run such an application, although it does say that any compliant Jakarta EE implementation must allow the user to perform a deploy operation on a standard packaged application. So more accurately: any given Jakarta EE implementation is a platform: you hand it a standard application, and its tooling can run that application.

Is CDI SE a platform? No. It is a framework. A framework is a library that, should it be poked through some other means, will arrange for your framework extension or participant to be called back (and hence started or poked, whatever that might mean, as well). CDI SE will look for certain classpath resources, but that’s not really packaging, exactly, and you can turn it off anyway, so ultimately you are the one doing the starting or poking of the framework and telling it what, in turn, to start or poke itself. Once you take care of that one way or another, your CDI SE framework extension or participant (your application) will do whatever the framework says it should do. So: framework yes, platform no.

Is Spring a platform? Yes and no. It is probably fundamentally a framework by the same logic, plus a collection of useful libraries you can use outside of the framework, plus some other stuff, plus a grand piano, some lead shot, the kitchen sink, a bank safe, and the fluff found in your front pockets. It also however does define a packaging format: if you build your Spring application a certain way, an executable archive pops out the other end that can be run by the Java platform (which also relies on a very complicated custom classloader embedded into the tail end of the ZIP-formatted archive by Spring!) or by a suitable Jakarta EE web container. So in that sense that part of Spring is a platform. On the other hand it leans on Java itself to do the heavy lifting if you execute one of its fat (and I do mean fat!) jars, so the recognizing that there is a Main-Class that has to be executed is done by Java itself, not by Spring.

Is DropWizard a platform? No, not really. DropWizard, like Spring, is a collection of libraries it defines and, unlike Spring, those from other places. It recommends, but does not define, various packaging formats. It wants you to run your program as a plain old Java program. Notably, DropWizard, while strictly speaking is probably a framework, delegates to other frameworks (like Jetty) to do the heavy lifting. Bottom line: not a platform, but a collection of useful libraries and frameworks.

Is Java a platform? Yes. It defines how you package your application and how such packaged applications are run. Using the same command line tool (java) you can run several different applications (executable jar files, exploded class directories, JPMS modules) depending on what you supply to the tool. (Also Java is obviously a collection of useful libraries!)

So is Java running a program that is a Jakarta EE implementation that deploys a Jakarta EE application two platforms? Yes, but in that picture presumably only the Jakarta EE implementation would be the platform of interest.

Is MicroProfile a platform? No. It is a framework as currently constituted, kind of. Actually, it’s not even really that, since there’s no entry point to a MicroProfile application, so no real defined way to poke it or start it. Like DropWizard, it relies (exclusively) on other frameworks (like JAX-RS) to do the heavy lifting, which do define such entry points. Nor is there a notion of a MicroProfile application that you start in any way. Nor is there a notion of deployment. Nor is there any common way to package a MicroProfile application even if there were a notion of what one is. Instead, I suppose it is a collection of useful libraries, and in some cases only parts of useful libraries, where the other parts are off-limits in some currently unspecified way. To use the language of Jakarta EE, it is, as currently constituted, “little more than bundles of APIs with few or no tie-ins” to a (nonexistent) larger platform. Maybe this will change.

If I have some arbitrary executable binary in my hand and I ask my computer to run it, is there a platform involved? Of course at some level there is, but I personally stop here, so therefore, dear reader, you will too: yes, a Unix system is a platform that runs, say, ELF executables, but in that parlance I guess I would be interested only in ELF executables that run other packaged applications. So, for this discussion, no, if I have an arbitrary executable (such as a compiled and linked C program) that just runs and does its thing, it is not a platform.

If I make a binary using GraalVM’s native image facility, is the resulting binary a platform? No (unless I’ve deliberately created a binary to run well-defined packaged applications of some kind, of course). See the logic above.

So is Quarkus a platform? No, because it just results in single purpose binaries. Quarkus is, really, a kind of compiler, I guess.

Is Helidon SE a platform? No; it’s a collection of libraries.

Is Helidon MP a platform? No; it’s a MicroProfile implementation and you’ll see above that MicroProfile isn’t a platform.

Is OpenLiberty a platform? Weirdly, although they define a runtime that can run well-defined packaged applications, they define themselves as a framework. I disagree; they are a platform: you deploy a well-defined packaged application to a simple server. Platform all the way.

Is Payara a platform? Yes. Depending on the product in question, it is either a Jakarta EE implementation of some kind (and hence a platform; see above) or defines a way of running applications (it is a MicroProfile implementation, and although as noted above MicroProfile is not a platform a runtime that defines a packaging format that happens to use MicroProfile’s useful collection of libraries is thus itself a platform).

Is Oracle WebLogic Server a platform? Yes; among many other things it is a Jakarta EE implementation.

More to come that may tie back to this article.