If you `docker pull` an image, you already "host" it. It's a bunch of local files right on your machine.
Starting a few minutes? It looks like there must be some DNS problem somewhere. Or maybe it's the download build time? In any case, I'd measure the second startup time.
Java can be blazingly fast if done right. (And C++ can be stupidly slow if done wrong.)
I'm aware Java can be fast, but thats never what I work with. The products I've supported include vmware vcenter, confluence and epo. In all cases, just restarting a service is a "go have a coffee" affair. It really says a lot that something can take longer than a Microsoft exchange server to start but when I see it, I know someone badly wrote a Java app. To be clear I'll happily buy that this is a case of it not done right, but that seems pervasive.
Those services were all built to not be restarted so they've never optimized for it. More recent Java frameworks and projects do try to optimize restarts due to kubernetes adoption etc.
Every newer Java application I've seen is just as dog slow as those older ones. Keycloak itself being a prime example — it was rewritten on top of Quarkus recently, and it didn't help much. You're still expected to build a second image (and maintain it — it wouldn't be a problem if you only had to it once), and it still takes 2-3 minutes to become responsive.
You may have have seen those magical Java applications that both implement a decent amount of functionality (so not just a toy), and start in a couple of seconds, but the rest of us will believe it when we see it.
I wonder how they're developed, it feels like a throwback to the punch-card era.
While I don't have much love for Microsoft, you should take a look at dotnet. Applications written on top of dotnet (even using massive frameworks like ASP.NET + EF) actually do start in a few seconds, which is at least an order of magnitude faster than anything similar in Java.
Starting a few minutes? It looks like there must be some DNS problem somewhere. Or maybe it's the download build time? In any case, I'd measure the second startup time.
Java can be blazingly fast if done right. (And C++ can be stupidly slow if done wrong.)