Regarding Stacks, Runtimes, and Remote Descriptors
This email is to try to begin discussion on some recent duplication of
code and responsibilities, which should probably be fixed before things
get too comfortable. I'm speaking specifically about the role of
discovering runtimes to download, where that's done, how that's done,
and which responsibility belongs to who. Forgive me if the email is
long, as I am trying to be thorough.
Currently, there are three places from which runtimes to download may be
1) base/runtimes has an extension point named downloadRuntimes, which is
used by AS Tools and Seam Tools (and perhaps others).
2) a remote descriptor file which acts as a second arm of 1) and is
basically an xml form of 1) used to dynamically add new runtimes as they
3) The new Stacks methodology, currently stored in
We should begin unifying these three locations into one, but the goal is
to do it correctly. So, I would first like to list the benefits of each.
a) downloadable runtimes provided through the extension point cannot be
removed without a maintenance or major release of some type, and for
this reason are semi-permanent
b) downloadable runtimes available via the remote descriptor file may be
added OR removed at will. This provides flexibility and post-release
updates are easy.
c) The new stacks section has a more robust model capable of providing
more information than the downloadable runtimes does. However, the
plugin requires several libraries and is currently placed in the
jboss-central module, where others may not make use of it.
d) the Stacks yaml file does not provide a place to access the file size
for the download, however it does provide a 'labels' section, which
seems extendable to add whatever properties you may want to add.
At first glance, it seems that Stacks is the superior framework. It is
extensible, it can have unlimited labels (aka properties) if desired,
and it already provides more information which is usable to others who
may want it. To make use of stacks inside Runtimes, however, we'd either
a) Expand the API in runtimes to allow other plugins (like in
central) to provide downloadable runtimes, or,
b) Push 'stacks' out of central and down into runtimes, as its own
plugin upon which runtimes.core and runtime.ui can depend.
The main negative of pushing stacks into base/runtimes, in my opinion,
is that there are a significant number of libraries required. It's not
too much, by far, but it is about 7 jars totalling about 1 megabyte.
Whether these jars belong in base/runtimes is debatable, and currently
we do not have a "3rd-party dependencies" section in base where we
organize common dependencies and versions together so that each plugin
doesn't need to bundle their own 3rd party libraries. I admit, this is a
debate for another time, but, I just wanted to point out that pushing
the stacks logic down into runtimes would be another example of this issue.
Even still, I would argue that we should push stacks into its own small
plugin below runtimes, deprecate the "downloadRuntimes" extension point,
and the online downloadRuntime.xml (wherever the file is, I forget).
However, once we do that, there are many more questions. The first is,
who's job is it to provide the yaml file from which stacks are generated?
Currently there is only one yaml file, and it is referenced directly via
a github url. Aside from how (IMO) this is fairly crazy in itself, it
causes another problem. The stacks client jar *can* cache the yaml file
and only update if the timestamp has changed, however, when checking the
timestamp on a github file, there isn't one...
This would seem to imply we should take control of the yaml file
ourselves and put it NOT in github but rather in a release-specific
online-accessible folder, ex: jbt4.1/stacks.yaml, jbt5.0/stacks.yaml, etc.
The problem with this is that we are then taking control away from the
jdf team, and once we take the file away, it is our job to keep it
updated and in synch. This may cause errors if we are not very careful.
Assuming we do this, though, the next question is, do we add seam and
esb runtimes to this yaml file, which currently only provides
application servers? Remember, the purpose of moving stacks down would
be to deprecate the downloadRuntime extension point, therefore any
replacement would need to do everything downloadRuntime does, which
includes providing seam and esb runtimes for download.
Let's assume (for now) that we simply add lines to the yaml to allow it
to provide seam and esb runtimes. We may come back to this point later,
but for now, assume we do that.
Then which plugin will provide the url to our copied yaml? Who's
responsibility is it to point to this yaml file? Let's look at our options:
1) The runtimes plugin references the yaml
2) The central plugin references the yaml
Both of these fail after thinking about it. How?
1) If the runtimes plugin references the yaml, then the download
runtimes dialog will list things (like seam) which may not be present in
the installation. Imagine an installation with only base and server
plugins installed, and so no seam or esb. A user clicking 'download
runtimes' will see esb and seam downloads, but the plugins which are
prepared to handle those runtimes after the download are not present.
2) If central is in charge of providing this yaml, perhaps through a new
extension point to the base/runtimes/stacks plugin we add there, then an
installation including only plugins from base / server will have a BLANK
download list. Users who install only ASTools will not be able to
download JBoss Application Servers.
So both of these fail in their own way. The only solution as I can see,
the only way it would work, would be to have multiple such yaml files,
one for astools, one for seam, one for esb, etc. Each of these modules
would provide their own yaml url to base/runtimes/stacks via an
extension point in base/runtimes/stacks, and let stacks fetch each one
and build a unified model.
a) multiple urls need to be loaded
b) multiple yaml files need to be kept up to date, instead of just
one. Multiply number of contributing plugins by number of major releases
c) Possibility of duplicates. Once you have multiple yaml files
generating models, it's possible some duplication leaks in. I'm not so
sure about this one, but Fred listed it as a concern.
So, by my analysis, this is the only way I can imagine a unification of
these three models. I'll summarize the changes below, but it does seem
there would be a bit of work to do.
Summary of changes:
1) Deprecate downloadRuntimes extension point
2) Create new plugin in runtimes module called "stacks"
3) Add extension point to 'stacks' plugin called stacksProvider
4) modify runtime.core and runtime.ui to use the model built in 'stacks'
5) Create a web-accessible location for jbt-release-relevent data on a
per-module basis. For example,
6) Copy the current jdf yaml file to that location for astools.yaml
7) Create a new yaml file which can build stacks for esb, seam, etc
8) Ensure astools, esb, seam, etc, make use of the new stacksProvider
9) Test the shit out of it
There are other benefits to this approach. Currently there's no really
good mapping of downloadRuntimes id's to an app-server id. This is done
in a hard-coded fashion in astools. This could instead be added to the
labels in the astools.yaml file if desired. It would allow dynamic
addition or removal of any runtimes, though in the yaml syntax. It would
minimize connections and re-downloads of the yaml files, since they'll
actually have a timestamp now (as opposed to in github, where they
don't). And it could help clean up some other areas that could benefit
from a cleanup.
I'd really like feedback on this issue from anyone who knows anything
about the topic, because I know for sure I'm lacking a bit in fully
understanding the entire api. But I'd love at the least for someone to
tell me which of the logic here is obviously bad or if i'm wrong on any
Thanks and look forward to the feedback
- Rob Stryker
I break things, and then put them back together.