I think you intended that message for me, not Brian. Thanks much for the 
feedback. I have been reading about Kubernetes, but I got discouraged when I 
saw that they dropped Docker support, since Docker seems to be the most popular 
containeriziation technology. Also, most of the Kubernetes tutorials I saw on 
YouTube seem to approach it as a dev platform, and we're not developers.


> -----Original Message-----
> From: Guido Jäkel <>
> Sent: Monday, June 28, 2021 2:43 PM
> To: Brian Wolfe <>
> Cc: Tomcat Users List <>
> Subject: Re: 500 instances of tomcat on the same server
> Dear Brian,
> please take the time to read about Linux Kernel namespaces as the technical
> base of containers. It's like two viewpoints to one thing. Take the network
> namespace as an example: From the conceptual point of view it looks like
> you have N indipended, functional identical "IP Stacks". But from the
> technical point of view, it's just the "well known" single instance just with 
> an
> additional field at all items that need this (packets, routing tables, ...) 
> to take
> a tag value that identify the namespace instance.
> You may use namespaces with the raw tools like enterns or with LXC or
> Dockers. During runtime of a started container, there's nothing more you
> have to trust but the kernel because for the basics, there's no need of
> additional userland processes to keep a container running.
> To run an application in a "container", you start it with a bunch of 
> instances of
> this namespaces, at least the process namespace. You'll probably take the
> same name for the technical namespace instances - from the conceptual
> point of view this is the name of the container.
> Most will start something like the init binary located in a directory tree of 
> a
> small Linux distribution userland. This may "boot" common services and the
> result may act like an "indipended platfrom". But you may also launch just
> single high-level applications like a JVM running a Tomcat.
> That's very close to your architecture, but much more easy to handle. For the
> network stack e.g. you may use the same ports for listeners and have the full
> range of ports available for connections in each namespace. There are
> different ways available to route the traffic, but in any case you may use
> individual IPs in each namespace.
> greetings
> Guido
> On 2021-06-28 19:22, Brian Wolfe wrote:
> > Generally, I'd agree too. We are considering using containers, but I'm
> > not yet sure what that buys us in terms of stability.
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