On 19 Dec 2005, at 14:54, Jules Gosnell wrote:
James Strachan wrote:
On 19 Dec 2005, at 14:14, Jules Gosnell wrote:
James Strachan wrote:
On 19 Dec 2005, at 11:53, Jules Gosnell wrote:
, whether there is other suitable Geronimo or ASF-licensed
code available, or whether we will need to write our own
WADI- autodiscovery classes. The important thing is to impose
as few dependencies on the client as possible. The client
side code should literally be a few lines. Clients using
clusters should not suddenly find themselves sucking down
e.g. the whole of activemq, just to do a once off
autodiscovery. Early versions of WADI had its own
autodiscovery code. If we need them, they could be resuscitated.
There's no reason why you can't do a simple implementation of
ActiveCluster which doesn't use ActiveMQ - its just a simple API.
Sure - but I'm talking about the EJB-client side - where we just
want to throw across as thin a line as possible, in order to haul
a decent strength cable back. An EJB client would not need the
ActiveCluster API (I'm not thinking in terms of making EJB
clients fully fledged cluster members), but simply a way of
locating the cluster and requesting a membership snapshot of it.
Thats exactly what the ActiveCluster API is for :). Though by all
means come up with another API if you can think of a better way
of doing it.
This could be done by just broadcasting a query packet at a well
known multicast address and waiting for the first well-formed
response.
Sure - an *implementation* of ActiveCluster API could do exactly
that.
???
well, maybe I'm thinking of the wrong piece of activecluster then ?
any piece of code could broadcast a packet... which piece of
activecluster's API are you suggesting here ?
You said...
but simply a way of locating the cluster and requesting a
membership snapshot of it.
The entire purpose of the ActiveCluster APi is to locate members in
clusters & be informed when they go down. There's a zillion ways of
implementing this - AC just tries to be a common, simple API we can
share.
we really are talking about just a remoting proxy which needs to
find, but not 'join' a cluster.
AC can be used purely to discover nodes and choose which one to use
as a server. The local in-JVM node does not actually have to actually
advertise itself to members of the cluster if it doesn't wish to -
thats an implementation detail. (e.g. if you only want servers to be
discoverable but keep clients invisible).
Using the EJB client and server side example - you may want to know
which clients are connected to what servers so that you can load
balance; so even though you may not consider clients as 'members of
the server cluster' being able to know who is connected to who is
quite useful. EJB clients could expose statistics that can be used to
help choose the right server a new node should join.
But whatever - if you don't wanna use the AC API its no big deal; use
whatever abstraction you see fit - I just wanted to explain the point
of AC; for discovering nodes in a cluster and being able to choose
which one to communicate with; it can be implemented any way you like
(simple multicast stuff, using HTTP, LDAP stuff etc).
Maybe it'd help if we separated AC into the 'messaging' part and the
'discovery' part?
James
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