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From Jean-Baptiste Onofré ...@nanthrax.net>
Subject Re: Possible feature features
Date Tue, 18 Jan 2011 06:22:01 GMT
Hi David,

my comments inline:
> 1. maven-generated features.xml and maven feature packaging type.
> Geronimo has some code that basically generates a features.xml that includes the (appropriately
scoped) pom dependencies and transitive dependencies, stopping when a dependency is a feature.
 It even works with maven 3 :-) (AFAICT the current generate-features-xml mojo does not).
 I haven't been able to figure out what the current geronimo-feature-xml mojo tries to do
but it appears to be something else.  So, the output from such a maven project would be a
features.xml file with a single feature including all the transitive dependencies.  This is
a totally non-code project.  A feature maven packaging type would then deploy this as the
sole generated artifact for this project.  Then you can refer to this project as a dependency
and it all fits into the maven infrastructure.
We have the features maven plugin:

Using the features plugin, you can:
- features:generate-features-xml to generate the features XML
- features:add-features-to-repo which reads a features descriptor and 
resolves artifacts to the local repo

FYI, we raised a JIRA to rename this maven plugin with a more generic 
name: karaf.
The purpose is to provide new goals such as karaf:branding, karaf:run, 
karaf:distribution, etc.
Of course, the existing goals will still exist: 
karaf:generate-features-xml, karaf:add-features-to-repo.

> 2. .kar files
> I just found out about .kar files today.  IIUC this is a jar file that contains a feature.xml
and the bundle dependencies listed in the feature.xml.  I think an additional mojo and packaging
type that generates the feature.xml as in (1) and then packages it and the bundles listed
into an archive would be a good idea.
Agree, it's in the plan of the "new" generic karaf maven plugin:
- karaf:kar goal will take just a features descriptor (and eventually 
some resources) to create the kar by packaging the features description 
plus the bundles set
I raised a JIRA about that: KARAF-401.

> 3. resources in .kar files
> Geronimo .car files can include resources that get unpacked on installation into the
server directory structure. While normally osgi bundles are supposed to look for their data
in their own osgi-managed data area, sometimes you need something that the user can find :-)
and it really belongs in a well known location not associated with a particular bundle.  In
particular, in geronimo we use this idea in server assembly.  We have a .car file that has
the basic directory structure of a server and the startup jars packed as resources.  When
assembling a server, we start with this .car file and unpack the server structure out of it.
Yeah, as I said before, the kar goal could contains an instructions 
(with includes/excludes tags) to embed resources into the generated kar 

> 4. server assembly
> (cf. KARAF-56)  Karaf really needs a really simple way to assemble a custom server using
maven. Based on geronimo's experience, one way to do this would be using a maven plugin that
installed features and .kar files, using the resource-in-kar idea from (3).  You'd use a server-assembly
packaging and list all the features and kar files you want as dependencies, and the plugin
would install them and pack up the result.
Agree. I'm working about this.
The first step is to rename the features maven plugin into karaf maven 
plugin to avoid to lost the users with several plugin name.
On the karaf maven plugin, the dist goal will create and package a 
custom karaf container.

> Comments
> When assembling an osgi server, there's a battle between osgi/obr "I need these packages/services"
and maven/file-system/require-bundle "I want this artifact".   When a feature lists an artifact
to install, its definitely on the "this artifact" side of the line.  What do you do when you
get to something you need but don't want to include in the feature?  you can either specify
the external requirements as Import-Package and some kind of require-service specifications
or specify e.g. other features whose bundles provide the requirements.  Geronimo has used
something similar to the "specify other features" approach.  Aries EBAs specify osgi package
requirements.  If you want to assemble a server with the minimum input information, relying
on feature dependencies is very simple.  However it makes it harder to use alternate sources
of packages and services.  One idea I had was to associate an OBR repository.xml with each
feature that includes the OBR info for the bundles in the
 feature.  Then you can create a "virtual" OBR from a set of features by including all the
repository.xmls from the features.  If a feature specifies its external requirements both
as osgi requirements and as feature dependencies, an installer/assembler could check if each
feature dependency is needed to satisfy the osgi dependencies before installing it.
We added the obr resolver in a feature.
If we package an OBR repository.xml in a feature, I could be append to 
the Karaf instance OBR.
 From my point of view, the OBR should be manage:
- by the Karaf instance itself
- by the provisioning tool
As we can consider the feature as a provisioning tool, it makes sense 
that it can provide an OBR repository.xml.


> ----
> I'd really appreciate comments on these ideas.  I'm going to start seeing if I can munge
the geronimo code to do some of this either in a karaf sandbox or in git.  Having some code
to try out may be a lot clearer than my sometimes convoluted explanations...
> thanks
> david jencks

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