Information Technology Reference
In-Depth Information
6.4.3
Summary
The nextServer round-robin recovery routine provides a simple method of error
recovery for a large proportion of applications. In the event of an error, the next
server in the list of servers is used as the current server and a failure in all servers
called in sequence (that is calling all servers in the list and receiving an error or
no response from all of them) causes the application to terminate, thus avoiding
an endless loop.
While this provides a simple and effective recovery scenario for many classes
of applications, it cannot support the scenario where server processes come and
go on the network - i. e. the spontaneous network model [117]. To support this
model, and to evaluate the extendibility of RemoteJ's recovery capability, we have
developed a server plugin and associated client class which is called directly from a
user-defined recovery routine allowing a new server to be selected using a multicast
technique.
This has demonstrated that RemoteJ's recovery model can be extended to
support sophisticated recovery scenarios without the client code being aware of
the recovery mechanism and yet still be able to participate in recovery scenarios.
6.5 Chapter Summary
The main goal of this project was to provide a contribution to the vision of auto-
nomic computing and to simplify the development of distributed applications by
modularising the distribution and recovery concerns and applying them to exist-
ing applications using a high-level domain-specific aspect language approach. As
we have demonstrated a number of protocol implementations, using different dis-
tributed systems concepts, and have demonstrated the flexibility of the recovery
concern, we believe we have succeeded with this goal.
Any claim to having provided an entirely new method of distributed systems
development that can replace current methods cannot be made until RemoteJ's
deficiencies are addressed and it can be tested and studied in a commercial envi-
ronment. We discuss these deficiencies and future work in the next chapter.
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