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Chapter 6. How to manage applications

Once the client nodes you need in your application are built, you can decide how you will allocate client nodes to hosts. In this section, we highlight the management of running applications, which includes launching the data flow servers and the client nodes.

Starting the data flow server

Before starting any client node, a NDFS-II network needs to be established. You can do that by launching data flow servers.

A NDFS-II network is at minimum composed of one host running a server. If you desire to use several machines in your application, you need to start a data flow server on each of them.

The system has dynamic properties: if you start a server and client nodes on one host and later on you need to launch more client nodes from a different host where no server is currently running, you just need to start a data flow server on the new host. The new server will then join the NDFS-II network if servers share the same application domain. A server can join or leave the network at any time: the system has been designed to handle this behavior.

After the new server joins the network, you can start client nodes that can interact with the ones already running on the network by exchanging data if specified.

If a server quits the network, every client node running on this host will be disconnected. It will then affect other client nodes, because they won't receive data anymore from producer client nodes that were running on the host, which has just left the NDFS-II network.

In order to establish a NDFS-II network, you only need to start the data flow server on each host. You can give a parameter when launching the server. This parameter specifies the application domain. If you don't specify anything, the default application domain is used. Every domain is logically separated from the other ones, meaning that client nodes producing or consuming flows are not visible outside the domain. Therefore a producer client node providing data cannot feed a consumer in a different domain even if the flows match.

The domain selection allows having several applications sharing the same subnet without any interaction between them. It is very useful when several people work using the system with different applications. Be aware that a physical host can only have one server running at a time and can only be part of one domain.

In order to start a server, you need to launch the executable file called sf2d and located in the bin/admin folder if you built the system using qmake or in the bin folder if you used the configure; make; make install method.

If you are willing to start the server using an application domain different than the default one, you need to specify it as follows:

sf2d myDomain 

Created on 2008-06-18 by Antoine Fillinger - Last updated on 2008-11-23 by Antoine Fillinger