[eldavido]

Just worked on deploying OpenAM on tomcat with Docker. A few things stuck out to validate the "hard to deploy in containers" point:

(1) node.js/Ruby/Python scale with processes, not threads. There's no supervisory/control environment over the processes, just the OS. JVM on the other hand expects to do a lot more process/thread control itself so it's kind of another "layer" between the OS and your code.

(2) Port binding doesn't work the same way, either. Most of our dockerized services have one port/process with simple load balancing built into our "routing fabric", which is something ops controls at my company. My understanding of JVM scaleout is that the servlet container is responsible for multiplexing incoming connections onto free capacity, which isn't how most docker shops work.

(3) I'm not sure what the typical deployment patterns are for servlet containers but they seem more multi-tenant w.r.t # of applications running in them, vs. a typical docker setup where containers are very thin and meant to be run in the dozens or more per-machine.

It's not that the JVM is inherently inferior, more than Docker has grown up around unix/linux ops-minded folks and they're bringing a lot of their assumptions about how software should be deployed and operated (e.g. "things should be scriptable") with them, and that their thinking is dominant among the current container-using crowd.

[brown9-2]

My understanding of JVM scaleout is that the servlet container is responsible for multiplexing incoming connections onto free capacity, which isn't how most docker shops work.

No, not really, typically you would just run N of your JVM processes with either some sort of load balancer (or your "routing fabric") to balance between them or a discovery mechanism.

I think you might be referring to some sort of big-box "enterprise" servlet container like Websphere or something quite different than Tomcat.