3:36 a.m.
I'd like to point out that the 'start.policy' property needed for OSGi
deployments is a workaround for the general lifecycle disconnect that we
have between AS7 deployments and OSGi deployments.
In AS7 we have
* ADD - bring the bytes across
* DEPLOY - parse metadata, resolve (a.k.a create module/classloader),
install services
* UNDEPLOY - remove services, destroy classloader, etc
* REMOVE - take the bytes off the system
In OSGi we have
* INSTALL - bring the bytes across, parse the metadata
* RESOLVE - (may be implicit) link to other installed bundles, create
the classloader
* START/STOP - (repeatedly) install/uninstall services
* UNDEPLOY - take the bytes off the system
The fundamental disconnect is that the AS7 DEPLOY operation is a an all
or nothing approach, which creates an ordering issue for the user. For a
large set of interconnected deployments, the user has to know in which
order they can be deployed. Generally, this ordering concern should not
be delegated to the user because he/she cannot know the complex
dependencies between deployment capabilities/requirements. IOW, given a
set of deployments the admin cannot know in which order they need to be
dropped into the deployments folder.
I'm mentioning this because I believe we might want to apply the
deferred start.policy behaviour to non-osgi deployments as well.
This raises the question about properties that should be shared between
subsystems? Brian's approach binds them to one subsystem only.
I would prefer a global set of properties that the deployment layer
knows about and can validate. These can be document and they become part
of the API. Any other prop is passed through but not part of the API (it
would not show up in console/cli). This is much like any other shared
concept that can be seen from any subsystem.
------
Making props be part of the deployment ...
One of the value propositions of OSGi is that you can easily bring in
functionality by deploying 3rd party bundles. Those bundles cannot be
touched. Properties that modify (bundle) deployment behaviour like
auto-start and start-level must be defined external to the deployment.
------
Concerning jboss-all.xml and using overlays ...
An overlay is currently not a child of the deployment itself. When you
undeploy the properties related to that deployment must get removed as
well, which is currently not the case with overlays.
cheers
--thomas
On 10/15/2012 11:45 PM, Brian Stansberry wrote:
I've been working $subject in order to help support Thomas
Diesler's
request for AS7-3694[1]. The gist of this request is to add deployment
unit processing (DUP) configuration as children of the deployment
resource itself. Thomas' OSGi use case is one place where this would be
used. I expect HASingleton deployment will be another.
WIP is at [2]. I'm looking for feedback. :)
What I've done is based on what Thomas did at [3]. What I want to do is
move from the generic key/value pairs in that patch to a more formally
describable management API. Instead of:
<deployment name="foo.war"...>
<properties>
<property name="start.policy" value="DEFERRED"/>
<property>
</deployment>
It would be something analogous to how a profile configuration is done:
<deployment name="foo.war"...>
<deployment-subsystem xmlns="urn:jboss:domain:osgi:1.2">
<start-policy value="deferred"/>
</deployment>
</deployment>
The existing Extension API already has the hooks to support this.
Extensions can register xml parsers for children of the <deployment>
element and can register management resources to act as children of the
/deployment=foo.war resource as well. Several subsystems already take
advantage of the latter. Until now the former has been an unimplemented
API. The commit at [4] implements it.
A couple things giving me some concern:
1) The above xml:
<deployment-subsystem xmlns="urn:jboss:domain:osgi:1.2">
Nicer would be something like:
<deployers>
<subsystem xmlns="urn:jboss:domain:osgi:1.2">
I need to figure out if I can do some tricks with the parsing to allow
that to happen.
2) The structure of the resource tree. We already support resources like
this:
/deployment=foo.war/subsystem=web
Subsystems register resources like those to expose metrics. The commit
at [4] uses that same tree. When subsystems could now register child
resources to the deployment=* resource, they could include both runtime
stuff and configuration stuff.
I'm not sure that mixing the two is ideal, although it's what we do for
the regular subsystem resources in the profile. I'm vaguely concerned
that if someday the configuration that subsystems choose to expose via
this mechanism gets complex, the mixing of metrics with configuration in
the same tree will start to break down.
Comments are appreciated.
[1] https://issues.jboss.org/browse/AS7-3694
[2] https://github.com/bstansberry/jboss-as/commits/AS7-3694
[3] https://github.com/jbossas/jboss-as/pull/3230
[4]
https://github.com/bstansberry/jboss-as/commit/6326003a104ac4ac825e8dda4c...
--
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Thomas Diesler
JBoss OSGi Lead
JBoss, a division of Red Hat
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