[jboss-as7-dev] Clustered invocation design

[David M. Lloyd]

There are at least two basic paths we can follow for clustered 
invocation based on the current architecture.  The right choice is going 
to depend primarily upon the expected use cases, which I am not in a 
position to properly judge.

Option 1: Clustered Invocation Transport
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In this option, we introduce a new "LAN" transport type for invocation 
on the cluster.  The transport would use direct TCP connections or UDP 
messages (or both, depending on request size) to convey the invocation. 
  The characteristics of this option are as follows:

- Security: reliance on physical network security only (no TLS or 
authentication)
- Latency is very low, even to new nodes
- Topology changes can be conveyed as separate asynchronous messages
- Invocations from external networks would happen through a proxy node, 
with Remoting being bridged to the LAN, to perform security functions

Option 2: Load-balanced Remoting Connections
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In this option, we rely on the client to establish one or more Remoting 
connection(s) to one or more of the nodes of the cluster.  Logic in the 
client will be used to determine what connection(s) to use for what 
clusters.  We have the option of automatically connecting as topology 
changes or requiring the user to set up the connections in advance. 
Note that automatic connection cannot work in the case of 
user-interactive authentication.  Characteristics:

- Security: full authentication and TLS supported
- Latency is low once the connection is established, however there is 
some overhead involved in authentication and security negotiation
- Topology changes should be asynchronous notifications
- Each connection has to be separately authenticated
- Automatically establishing connections is not presently supported, so 
we'd need a bit of infrastructure for that.  Deal with user-interactive 
authentication.  Deal with connection lifecycle management.  Deal with 
configuration.  This will be a point of fragility

Summary
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For both options, we have to determine an appropriate load-balancing 
strategy.  The choice of direction will affect how our clustering and 
transaction interceptors function.  We also have to suss out the logic 
around dealing with conflicting or wrongly-ordered topology updates; 
hopefully our existing policies will continue to apply.

-- 
- DML