[jboss-as7-dev] Extensions in host.xml + individual server overrides

[Brian Stansberry]

On 1/20/11 6:47 AM, Heiko Braun wrote:
>
> On Jan 14, 2011, at 5:10 PM, Brian Stansberry wrote:
>
>> ay back in April/May/June time we thought that we might have subsystems expose a limited number of configuration items that could be overridden at the host level. Those would be limited to things that logically vary by host, e.g. the size of some pool might be bigger on a monster machine.
>
>
> at the Neuchatel meeting we identified the same use cases:
>
> a) override host specific subsystem configuration values at runtime (i.e. JCA max-pool-size)
> b) read host specific subsystem metrics (i.e. current number of JCA connections in use)
>

For a read, there is a an address that specifically targets an 
individual server; the metric can be read from that:

[{"host" => "hostA"},{"server"=>"server1"},{"subsystem" => 
"datasources"}, {"datasource" => "XXX"}]

> IMO the current restriction for a) to be managed on the domain level is not sufficient.
> As for b) I don't yet understand how changes at runtime could be done through a system property.
>

Yes, Emanuel told me about your discussion. Glad you went through that, 
since you're right; the expression-based approach I described works for 
independently setting the value for each server at boot time, but it may 
not let us properly support changing the value at runtime. If we use a 
variable that references some property, we need a mechanism such that 
changing that property at runtime triggers runtime updates to whatever 
services used the variable. Or, some other approach altogether.

I'd very much like to avoid subsystems having to register a fixed set of 
server-level-overridable configuration elements.


-- 
Brian Stansberry
Principal Software Engineer
JBoss by Red Hat