Network Daemons Supporting Distributed Laboratories

The various software libraries available from the Georgia Tech Distributed Laboratories group require the support of network daemons in some circumstances. Generally these daemons serve as centralized repositories of information.

At the time of this writing, there are three daemons:

• format_server -- This daemon supports certain functionality in the PBIO library. In particular, the use of IOContext structures allows records to be encoded and transmitted without full format information. In this circumstance, the format_server maintains a database of registered formats and format IDs. Programs registering formats or decoding a new format for the first time contact the format_server.
• group_server -- This daemon allows cooperating DataExchange programs to get in touch with each other without requiring them to agree on well-known port numbers or resort to other means to convey port informatoin. Instead the group_server provides a simple name -> host/port lookup service.
• atom_server -- This daemon supports the Object Transport Layer, which underlies the MOSS object system. OTL encodes object references as lists of name-value pairs. In order to have the flexibility of general strings without the search overhead, OTL uses the atom_server to provide unique string->32-bit ID translation. Extensive caching occurs within OTL to minimize the performance hit caused by this external service.

Each of these daemons run as a separate process. Instances of each of these daemons run on the host marquesas.cc.gatech.edu to serve the gatech.edu domain. External hosts are allowed three days of free use of these daemons. This service allows us to more easily give external demonstrations and gives external users an opportunity to try out our tools with minimal setup. For extended use of the Distributed Laboratories tools, you should run your own instances of the daemons.

If you build PBIO, DataExchange and OTL on external hosts they will automatically configure those libraries to look for the relevant daemons on the host where configure was run. If no daemon is found there they will fall back to using our daemons on marquesas.cc.gatech.edu and issue a warning message. To switch over to using your own daemons, simply start the appropriate processes on the configure host. The processes will automatically put themselves in the background. They also check to see that they are not run multiple times and are thus suitable to run at regular intervals from cron. See the configure script options in the appropriate package for information on setting the server host and service domain for each daemon. The built-in hostname for each daemon can be overridden at run-time by specifying one of the following environment variables: FORMAT_SERVER_HOST, GROUP_SERVER_HOST, ATOM_SERVER_HOST.

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