The messages on the bus go back and forth

In a rare display of synchronised software development - a raft of NGS research and development projects have safely reached their final destination.

We are proudly showing off our cloud; our HARC acceptors are now accepting to an acceptable level; the new User Interfaces are on display in the Innovation section of the NGS web site; we have come up with a saner way to manage access to licensed software and the ngs-vo-tool to manage virtual organisation configuration has been released.

There will be more on HARC in a future posting. The rest have already been well and truly blogged.

This posting is about the what we are going to do with all our newly available free time in the final 7 months of the third phase of the NGS.

We are here to do the dull-but-useful bits and the dull-but-useful things we are concentrating on are those needed as the NGS and GridPP join forces to form the UK National Grid Initiative (UK NGI) within the European Grid Initiative...

• Incorporating the important features of the NGS's current 'INCA' monitoring service into a NGI one based on WLCG Nagios.
• Allowing the data collected by the NGS accounting service to be interchanged with that collected by the APEL (Accounting Processor for Event Logs) accounting service.

These two projects share one important feature, one they also share with DataMINX Data Transfer Service described in an earlier post. They all rely on a message bus based on ActiveMQ to pass information around.

Yes... you wait ages for a bus and then three turn up at once.

A message bus is simply a way getting a lump of data from A to B. The important bit is that your application does not need to know how to get from A to B - it just needs to hop on the bus at A and hop off again at B.

Finding a reliable route from A to B becomes somebody else's problem.

WLCG Nagios uses its message bus to pass the results of tests to a central monitoring service. Technical details can be found on https://twiki.cern.ch/twiki/bin/view/EGEE/UseLocalActiveMQForMessaging.

The latest APEL client sends records wrapped in messages rather than attempting immediate database updates. Again there are more technical details available from http://goc.grid.sinica.edu.tw/gocwiki/ApelHome.

In both cases, they are using the message bus to avoid information being lost when there is a backlog of data to be processed. As users of the UK public transport service are all too aware, buses are very good at waiting in traffic.