On Jun 9, 2010, at 2:59 AM, viola.lu wrote:
> The doc is clear for end-users to understand. thanks. But I have one
> question about multipoint failover.
> There are three servers:server 1. server 2, server 3, now i add server 2 as
> server 1 initial multipoint servers, server 3 as server 2 inital multipoint
> servers, an openejb client call server 1 using:
> failover:ejbd://[server 1]:4201( here i don't need add all servers to
> openejb client provider url, right?)
> then i shutdown server 1, openejb client should still work coz server 1 will
> failover to server 2, and if i shutdown server 2, then server 2 will
> failover to server 3. This is the specific multipoint failover scenario, am
> i right?
If I understand correctly, then right on all points.
To recap for possible doc benefit, sounds like this is the setup.
client -> server1 -> server2 -> server3
That should definitely work, but the start order would have to be the exact
opposite:
server3, server2, server1, client
And the overall outcome would be:
server3 starts
server2 starts
- static: connect to server3
server1 starts
- static: connect to server2
- dynamic: connect to server3
At this point all nodes are connected.
And then when the client comes online and connects to server1, it will be sent
the following dynamic list [server1, server2, server3]. That list is versioned
and will be dynamically updated in future responses from the server if other
servers join/leave the network.
Once the dynamic list is obtained, the original "failover:ejbd://server1:4201"
URL initially used by the client is no longer consulted and the dynamically
obtained list is preferred for all failover situations. This is built right
into the ejbd protocol and is the same for multipoint(TCP) or multicast(UDP).
Any method of connecting to a server will work -- "ejbd://server1:4201",
"failover:ejbd://server1:4201,ejbd://server2:4201", or
"multicast://239.255.2.3:6142". Upon first connect, the dynamic list is
exchanged and that original URL is ignored. Note for that reason using
"failover:ejbd://server1:4201" and "ejbd://server1:4201" is essentially the
same thing.
Should a situation arise where the client cannot connect to any of the servers
in the dynamic list, then the original URL is used one more time before failing
the request. Here is where the benefit of the "failover:" URL lies in that
multiple servers can be listed resulting in more than one fallback.
Should that fail as well, the request will finally fail and the remote bean
method invocation will result in an exception. The entire process is repeated
should the application code attempt another remote bean invocation. It is not
necessary to construct a new InitialContext.
Going to put this into the doc as well. Good questions! It's very helpful in
flushing out the documentation -- or lack there of :)
Keep them coming! It's a good way to fill out anything that isn't completely
clear.
Thanks, Viola!
-David
