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

Heiko, Following up a bit here on our #jboss-as7 discussion that I had to leave. This is a general topic area we haven't talked about in a formal way for a long time, and I'd appreciate your perspective. The only reason to have <extension/> in host.xml is if the HostController would need to load an extension module and interact with it to find out something about its subsystems. Only reason HC would need to do that is if there were some subsystem info in host.xml. Only place that would logically fit would be in the <server/> element. Way 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. However, since then I've gotten a fair bit of user feedback that folks are going to want to use variables in their configurations, and set those variables from the command line or from the <system-property> elements in host.xml. So, we need to support this kind of syntax in domain.ml: <pool size="${my.pool.property:10}" /> What that expression resolves to could only be determined at the server level. Once we support that kind of syntax, it can really be applied to anything. And if you can do that, the rationale for some kind of formal SPI where subsystems expose a limited set of server-level overrides largely disappears. And with that, the rationale for the <extension/> element in host.xml disappears. -- Brian Stansberry Principal Software Engineer JBoss by Red Hat