[jboss-as7-dev] Management proposal for attribute mutability

[Jason T. Greene]

Currently we have way too many read only attributes in our management 
model. This makes life harder for the management tools and/or makes the 
resulting UI a bit unwieldy.

In some cases this is just because we haven't polished subsystem 
management (PLEASE all subsystem authors look at this!). In other cases 
though it's intentional because it is either difficult or currently 
impossible to make hot changes to a particular attribute. This should be 
exceedingly rare. Users love hot updates, and it's a competitive 
advantage. So first we should strive to make it hot in the first place.

However in the case that the change is not hot, and a server reboot is 
too aggressive, we should still supporting making the changes by 
bouncing all services involved. After some debate on IRC we finally 
arrived at what is IMO a really good option for this problem:

write-attribute (impact-services=true|false)

The operation handler on such a non-hot attribute would then return an 
error if false (the default), but would continue and bounce everything 
needed if the value is true. In addition we would add some simple 
description metadata that would allow tools to handle it right away 
instead of reacting to the error response.

For a practical example look at datasources. Due to limitations in JCA 
we have to restart the resource adapter if the jdbc connection url 
changes. While it should be possible to one day make this change hot, we 
can for the time being still allow the user to type in a value. They 
would however be prompted with some kind of dialogue that would confirm 
the impact of this change.

-- 
Jason T. Greene
JBoss, a division of Red Hat