> -----Original Message-----
> From: Mark Thomas <ma...@apache.org>
> Sent: Monday, June 28, 2021 9:04 AM
> To: users@tomcat.apache.org
> Subject: Re: 500 instances of tomcat on the same server
> On 28/06/2021 14:53, Christopher Schultz wrote:
> > Eric,
> >
> > On 6/25/21 22:58, Eric Robinson wrote:
> >> We can run 75 to 125 instances of tomcat on a single Linux server
> >> with
> >> 12 cores and 128GB RAM. It works great. CPU is around 25%, our JVMs
> >> are not throwing OOMEs, iowait is minimal, and network traffic is
> >> about 30Mbps. We're happy with the results.
> >>
> >> Now we're upping the ante. We have a 48-core server with 1TB RAM, and
> >> we're planning to run 600+ tomcat instances on it simultaneously.
> >> What caveats or pitfalls should we watch out for? Are there any hard
> >> limits that would prevent this from working as expected?
> > If you have the resources, I see no reason why this would present any
> > problems.
> >
> > On the other hand, what happens when you need to upgrade the OS on
> > this beast? You are now talking about disturbing not 72-125 clients,
> > but 600 of them.
> >
> > If I had a beast like this, I'd run VMWare (or similar) on it, carve
> > it up into virtual machines, and run fewer clients on each.... just
> > for the sheer flexibility of it.
> That just moves the goal posts. You'll have the same issue when the
> hypervisor needs updating (which admittedly may need a reboot less often
> than the OS).
> > If this is already a virtualized/cloud environment, then I think
> > you're doing it wrong: don't provision one huge instance and use it
> > for multiple clients. Instead, provision lots of small instances and
> > use them for fewer (or even 1) at a time.
> But it adds the overhead of an OS for each instance. And costs if you have to
> pay for that OS instance.

The overhead issue is an important factor. The other is the fact that it's a 
canned app, supported by the publisher, and doing it our way pays big dividends 
in terms of that workflow.

> As always there are trade-offs to be made and the "right" answer will vary
> based on circumstances and what you are trying to optimize for. I do agree
> that, generally, more smaller instances will be a closer fit to more use cases
> but that is only a general answer.

Generally, I'd agree too. We are considering using containers, but I'm not yet 
sure what that buys us in terms of stability.

> Mark
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