[LON-CAPA-admin] Adding Access servers

[lucasm at ohiou.edu]

You'll presumably get a reply from Guy, but I'll see what I can answer.

On Tue, 29 Mar 2005, Todd Ruskell wrote:

> Hi all,
> 
> We're about to finally incorporate two access servers, and simultaneously 
> update our library server to 1.3.x,  and I have a couple of config questions 
> before we jump right in.  First, what I believe I understand I need to do:
> 
> 1) When asked, select "Access Server" when I install lon-capa, but choose the 
> same domain
> 2) Add the 2 access servers to the hosts.tab on both access servers and the 
> library server.
> 3) restart loncontrol and httpd on all machines
> 4) ask that the access servers eventually get added to the hosts.tab which 
> gets distributed in the tarball.


All this sounds right. I can't think of anything else.

> Now the questions to which I haven't been able to dig up answers in the 
> archives or faq-o-matic.
> 
> 1) If I have a course that uses resources from another domain, and I log into 
> the access server, will I be able to use those resources if the access server 
> hasn't propagated to the other domain's hosts.tab?

Access servers will directly access the non-local home server for 
materials. The machine needs to be in both hosts.tab. If you want me to 
add them, send the two extra lines and I'll take care of updating 
hosts.tab on our three.

 
> 2) I will now have 3 servers, call them library, access1 and access2.  In the 
> base installed mode, I'm guessing that I need to tell students to change 
> their habits and connect directly into access1 or access2, rather than 
> library.  Is that correct?  In this situation, I suppose it is also possible 
> that everyone logs into access1, while access2 sits completely idle until the 
> load limit on access1 is reached.  Is this true?  If so, this strikes me as 
> inefficient, which leads to:

We have defined an alias, loncapa.phy.ohiou.edu, that has two references 
in the Domain Name server. DNS hands out the name in a round-robin 
fashion. This does a pretty good job of evening the load. Once the student 
is logged into a particular server, they stay on that server.

In summer, I have our admin point the name to our library server only. 
This way I can play with updating our access servers. Students are always 
told to go to loncapa.phy.ohiou.edu.

> 3) In an ideal situation, I'd like to tell students to just go to, e.g., 
> loncapa.mines.edu, and have lon-capa or some other mechanism figure out how 
> to truly load-balance between my two access servers, but keep direct access 
> to the library essentially for faculty only.  I'm presuming this is possible.  
> What tools have been used, or are recommended to implement this?  I seem to 
> recall Mark saying something about DNS load balancing a while back, but it's 
> not clear to me if that's automagically part of lon-capa, or if I need extra 
> tools.

AH, yep - didn't read this yet 8)

You need to go to someone on campus that runs your DNS server and get them 
to enter it. In the end, it's pretty benign - just an entry that has the 
alias and the names it maps to. It is not automatically part of LON-CAPA.

LON-CAPA's load balancing comes into play when a machine is above a load 
of 2.0 (or whatever limit is set).

Good luck! The jump to 1.3.X is worth it.

Mark

> Thanks for your help,
> 
> Todd
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----------------------------------------------------------------------------
Mark Lucas					email: lucasm at ohiou.edu
252D Clippinger Lab  				phone: (740)597-2984
Department of Physics and Astronomy             fax:   (740)593-0433
Ohio University
Athens, OH 45701