On Jan 21, 2010, at 8:21 PM, David Blevins wrote:
On Jan 21, 2010, at 7:49 PM, David Blevins wrote:
On Jan 20, 2010, at 12:15 AM, Kevan Miller wrote:
3) Geronimo currently requires multicast for the failover
scenario. This is great. However, we should also offer unicast-
based support, also. I frequently encounter users who are unable
to use multicast in their environments. Providing unicast support
would be a valuable addition, I think.
Agreed.
Currently with the way that everything is designed we theoretically
only need to replace this class:
org.apache.geronimo.farm.discovery.MulticastDiscoveryAgent
Which is an implementation of the DiscoveryAgent interface. The
primary job of the DiscoveryAgent is to receive notifications about
services coming and going and then simply notify the other parts of
the system that are interested in this information. These "other
parts" implement this interface:
public interface DiscoveryListener {
public void serviceAdded(URI service);
public void serviceRemoved(URI service);
}
So basically the new DiscoveryAgent needs to have a way to receive
"service added" and "service removed" messages and send that info
to the listener.
It seems that a REST implementation of DiscoveryAgent would be very
useful as a lot of shops use it quite extensively already for
various administration and it actually lines up pretty close.
ServiceAdded might be a PUT and serviceRemoved a DELETE.
Seems with something that simple it wouldn't be too hard to do
anything else that's required to get it to broadcast around.
Another approach we could take is a DiscoveryAgent implementation
that is backed by a JMS Topic. It would be a closer match to
Multicast, though we'd have to do some additional work to figure out
how to ensure that the JMS Broker is not a single point of failure.
Having it be a single point of failure initially would be fine, but
we would eventually need to figure that out. ActiveMQ does have
some features in this regard, so it should hopefully be workable.
http://activemq.apache.org/how-do-distributed-queues-work.html
One option.
Bottom line is all we use multicast for is to move URLs around the
network, so some way to do that without multicast is all we need.
Just checking in on this. Was hoping to start a conversation that
might lead to deciding on an approach (REST vs JMS vs ?).
-David
