Paul McMahan wrote:
Thanks for initiating this important conversation. As part of the
clustering effort I would like to work on a new admin portlet that can
be used to visualize the cluster topology and do things like set
properties for the session managers, deploy/undeploy applications,
etc. I think that making this aspect of Geronimo intuitive and easy
to use will be a big differentiator in our favor. I would love to
hear everyone's feedback about this idea. E.g. given our current
direction does this idea make sense? and what should it look like?
If we are generally in favor of this idea then before proceeding I
would need help understanding certain fundamental concepts of our
approach, such as:
-- Will G have explicit knowledge and control over clustering or will
it just be "embedded" within the applications' logic/configuration?
Geronimo should have full knowledge at the container level.
-- Will G follow a deployment manager paradigm where a certain node is
in charge of managing the entire config and pushing it to the worker
nodes? Or will each node be responsible for its own configuration?
I don't know if there has been any discussion of this ? I think that IBM
donated a control panel of some sort but I haven't seen it and don't
know if it covers deployment.
There is some stuff of relevance in the clustering overview that I just
posted.
I would like to see a situation where you can [un]deploy to/from any
node in the [sub]cluster. This would perform the same operation on all
nodes in that [sub]cluster. Essentially, applications become 1->all
replicated data.
This is a very simplistic view - as it is probably not useful to
synchronise the lifecycle of instances of the same app around the
cluster, otherwise you can't stop one without stopping them all (but
maybe this is what you want?) - maybe we need a synchronised and
non-sychronised mode...?
Of course, it may be that this conversation has already been had and
decisions made elsewhere ? In which case, I would be interested in
knowing the outcome so that I can update the clustering overview and add
pointers to the necessary threads/people etc...
-- What component(s) of G will provide an interface to the clustering
metadata and config? Would it be possible to provide a single point
of control in G that can take as input a clustering "plan" and handle
the resulting deployments and node configuration?
I'm not aware that anyone has drilled down this far yet, into how a
unified approach might work, but I suspect that we will end up with some
form of ClusterGBean which provides the node's connection to the Cluster
(an activecluster.Cluster), notification of other nodes leaving and
joining, messaging primitives etc. A clustering portlet might register
listeners with this.
-- Is each member of a cluster assumed to be using an identical
configuration?
In a homogeneous cluster yes - but I think that we will have to cater
for heterogeneous deployments. There is a nascent section in the
overview doc about this.
-- Will G be able to participate in heterogeneous clusters with other
types of app servers and/or versions of G?
I don't know whether anyone else has considered mixing (a) appservers or
(b) geronimo versions in the same cluster - I haven't. I think (a)
unlikely (unless you are talking about e.g. a business tier that is
geronimo and a web-tier that is standalone Jetty/Tomcat, which I guess
might be possible, but i suspect that both tiers would just be geronimo
running different configurations), (b) is more possible, provided that
the protocols used by the different clustering components were
compatible. With the amount of complexity already surrounding
clustering, though, I think you would just be making your life much more
difficult than it need be.
Hope that helps,
Jules
Looking forward to your feedback and advice.
Best wishes,
Paul
On 1/26/06, *David Jencks* <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>> wrote:
I have some ideas about how to set up web clustering in terms of
geronimo modules and configurations and connections between gbeans.
I've talked with Jules and Jeff about this and think that they agree
that this is a good starting point so I'll try to describe it and
possibly even help implement parts of it.
There are quite a few questions I'm going to ignore, such as EJB SFSB
clustering and the new session module James and Dain wrote and how it
might relate to the web clustering stuff. We have to start
somewhere.
For me, one of the most important factors is that the clustering
solution be pluggable, in particular that you be able to run geronimo
without any clustering classes. This means that each clustering
solution needs to be packaged in one or more Configurations or
modules and that communication to the clustering module be done
through interfaces defined in a more core geronimo module. It also
implies that the all the web containers should communicate with the
clustering implementation through the same interface(s).
I'm proposing that the interfaces be SessionManagerFactory and
SessionManager, the factory being able to provide SessionManager
instances. I see the SessionManagerFactory being deployed as a GBean
and made available to web containers through a gbean reference.
My understanding is that for both jetty and tomcat, the web app
context needs an instance of a session manager. Therefore I propose
giving each web app context a reference to the session manager
factory gbean. At an appropriate lifecycle point it can get the
session manager it needs. In Tomcat IIUC a host or engine can also
be where a session manager is configured. We don't really need to
support that directly since we can in our deployer push a reference
to whatever "global" session manager may be configured down into each
web app context.
I see the jetty and tomcat builders installing references to
appropriate session manager factory gbeans. IIUC there is a lot of
configuration possible for at least WADI, and we should be able to
support running multiple session manager configurations at once, as
follows:
- there can be a default session manager (say WADI) configuration,
and the name of its session manager factory gbean can be configured
in the web app builder(s). This will be used for distributable web
apps that don't specify in their plan a different session manager
factory gbean.
- a web app plan can contain an explicit reference to a specific
session manager factory or an entire session manager factory/WADI
configuration.
- we can use a namespace driven xml-reference builder to construct a
wadi configuration inside a SMF reference (maybe :-)
There are a couple loose ends I can see and probably lots more I
can't:
-- I imagine we want to be able to have pluggable session managers
for non distributable apps or in the absence of clustering. I don't
know if we'd want 2 "default" session manager factory gbeans
available, one for cluster and one not, or if there is a better
solution. Having 2 and having the builder decide which you get seems
simplest at the moment.
-- We need to be able to support the non-wadi existing tomcat-
specific clustering, and it is unlikely this can be coerced
effectively into the proposed geronimo SMF and SM interfaces. We
could support this with another gbean and interface, but at the
moment I'm leaning towards giving the web app context either a
separate gbean reference to the tomcat specific clustering or
directly installing the tomcat solution into the web app context.
Comments? Flames?
thanks
david jencks
--
"Open Source is a self-assembling organism. You dangle a piece of
string into a super-saturated solution and a whole operating-system
crystallises out around it."
/**********************************
* Jules Gosnell
* Partner
* Core Developers Network (Europe)
*
* www.coredevelopers.net
*
* Open Source Training & Support.
**********************************/
