Re: LAS cluster & LVS

[Jonathan Callahan <Jonathan.S.Callahan@xxxxxxxx>]

CCH,

You've identified and interesting problem.  You are correct that a single LAS metadata table contains only one product server URL so the problem you are seeing is the one I would expect.  We have not experimented with using the localhost URL to get around this.  But I would expect you to be able to create a load balanced URL for the product server in the same manner that you created one for the user interface server.  Each LAS is truly broken up in to two completely independent servers (UI and Product) that rely on the metadata database to stay in synch.  So you should be able to put the product server behind a load balancer the same way you put the user interface server behind one.

But there is another solution entirely.  Our notion of 'sister servers' is that two servers will divide up the ownership of data, each owning it's own set of associated XML configuration files.  All of the requests for dataset A products will be handled by LAS A, dataset B products by LAS B.  Setting up LAS 'sisters' means that the LAS installations share the configuration files after the two independent LAS are set up.  Then the user interface servers of A and B can present the complete set of data while the product servers associated with A and B only handle requests associated with the data they 'own'.  This does not do any dynamic load balancing, but it does scale well and does not run into the problem you have mentioned.  I believe this is how the ECCO folks have united the SIO and JPL servers into a single interface:

http://www.ecco-group.org:8080/lasxml-org/servlets/dataset


In your case I'd try again to get the product server set up as a URL within your load balancer.  You can test it independently of the LAS UI by using the ls.pl and lasget.pl scripts in ~las/bin/.  If you get that part to work you should definitely be able to set up the configuration files so the UI servers will reference that URL.  We would be very interested writing some documentation based on your experience if you get this to work.


-- Jon




cch wrote:

 

Dear all,

 

The architecture of our system is in here http://water.ee.nsysu.edu.tw/~jianhong/.

We have two LAS servers ( maybe 4 LAS servers in the further. ) and one load balance server, but the sister server is not yet now.

In LAS A and LAS B, we installed all packages individually. ( includes UI server and Data server, MySQL, Ferret ... )

But the two LAS servers share a metadata database, that is,

we only have to maintain one XML configuration files ( las.xml, ui.xml, operations.xml, options.xml and all datasets XML files ) in LAS A.

After we execute "genLas.pl" on LAS A, the metadata database will be refreshed.

So, no matter the users connect to LAS A or LAS B, they will get the same content on their browser and get correct output.

( We directly connect to LAS A or LAS B, do not through the sister server now)

 

Before I write this letter, we consider this archetcture is available.

Unfortunately, there is a problem occurred.

 

In the "las.xml", it sets the url of Data server as following lines.

 

<operations url=""http://172.16.66.74/las-bin/LASserver.pl">http://172.16.66.74/las-bin/LASserver.pl">
      &operations;
      &insitu_operations;
</operations>

 

This means if a user connect to LAS A, the UI server of LAS A will dispatch the XML request to the Data server of LAS A.

But if the user connect to LAS B, the UI server of LAS B will also dispatch the XML request to the Data server of LAS A, rather than LAS B.

It results in the Data server of LAS A is very busy, but the Data server of LAS B is always idle.

 

We attempt to modify the url as http://127.0.0.1/las-bin/LASserver.pl.

Although this lets no Data server be idle, but the user can't get the output,

the output window will tell user that it can't find the output file in local machine.

 

We also attempt to modify the url as load balance server's IP, that is, url="" href="">http://172.16.66.73/las-bin/LASserver.pl.

but it is not work, after I select view, output, region and then click "Next", the error message of java occurred.

Maybe the reason is that the configuration of CVS of load balance server is not setting well, we will continue try it.

 

Another solution is every LAS server maintain an individual metadata database and individual XML configuration files.

It is the worst solution.

 

We think after sister server is ready, it may exist many problems.

Does anyone has any suggestion for this problem? or for this architecture?

Thanks very much.