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Thread: How to make application connect to multi-master set-up?
How to make application connect to multi-master set-up?
country flaguser name
India		 2007-02-19 08:43:56 

  


  

    
Hi,
  
 
  
We have a weblogic app server based application which talks to RedHat LDAP through weblogic's security provider APIs.
  
 
  
On Production env we have set-up master-master LDAP servers i.e. there are two master LDAP servers. How should i make my application connect to these 2 servers?
  
 
  
Should there be a front-end load balancer to which my application will make request and then load balancer will handle requests to one of the LDAP servers?
  
 
  
Also note that we have weblogic cluster in Prod with 2 instances. So should i make each instance point to one LDAP server? But in that case how will automatic failover work if one of the LDAP servers go down?
  
 
  
Would be great if people can suggest any standard solution to deal with such situations. 
  
 
  
regards,
  
Ankur
 


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    Re:  How to make application connect
to	multi-master set-up?
  


  

     country flaguser name
United States		
     2007-02-19 08:52:36
  


  

    
Ankur Agarwal wrote:

> We have a weblogic app server based application which
talks to RedHat 
> LDAP through weblogic's security provider APIs.
>  
> On Production env we have set-up master-master LDAP
servers i.e. there 
> are two master LDAP servers. How should i make my
application connect 
> to these 2 servers?
>  
> Should there be a front-end load balancer to which my
application will 
> make request and then load balancer will handle
requests to one of the 
> LDAP servers?
>  
> Also note that we have weblogic cluster in Prod with 2
instances. So 
> should i make each instance point to one LDAP server?
But in that case 
> how will automatic failover work if one of the LDAP
servers go down?
>  
> Would be great if people can suggest any standard
solution to deal 
> with such situations. 
>  

Typically this functionality is built in to the client (or
in fact the 
LDAP client library).
Interposed proxies or load balancers are possible with LDAP
but not 
normally needed.
I'm not sure about weblogic specifically but usually you get
to 
configure two or more
LDAP servers, or you can use multiple A records in the DNS.
I'd ask BEA 
-- they
should be able to tell you.





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    Re:  How to make application connect to
multi-master set-up?
  


  

     user name

     2007-02-19 08:52:40
  


  

    

  


  

    Interesting question. Yes a hardware load balancers works perfectly. In the configuration of a load balancer you create a virtual IP address and it will split off the requests between two servers. 

I accomplished rougly the same thing with linux-ha. I created two Virtual IP addresses. Pointed half the apps at one and half the apps at the other. Both of them will fail over to the other side.


What I want to do but did not have the time is use the Linux Virtual Server Project. Ontop of linux-HA. In this way the VIRTUAL IP can float between the two productions systems. That is really the best way to go. (and you save on the cost of load balancing hardware) 


There might be some ldap proxy software (sun makes something I think) that can prooxy ldap and redirect it in a HA type way. I have not looked into that. If you go with the linux virtual server project keep me in the loop. Let me know how it turns out.


Edward

On 2/19/07, Ankur Agarwal < ankur_agwalyahoo.com">ankur_agwalyahoo.com> wrote:


Hi,
  
 
  
We have a weblogic app server based application which talks to RedHat LDAP through weblogic&#39;s security provider APIs.
  
 
  
On Production env we have set-up master-master LDAP servers 
i.e. there are two master&nbsp;LDAP servers. How should i make my application connect to these 2 servers?
  
 
  
Should there be a front-end load balancer&nbsp;to which my application will make request and then load balancer will handle requests to one of the LDAP servers?

  
 
  
Also note that we have weblogic cluster in Prod with 2 instances. So should i make each instance point to one LDAP server? But in that case how will automatic failover work if one of the LDAP servers go down?

  
 
  
Would be great if people can suggest any standard solution to deal with such situations. 
  
 
  
regards,
  
Ankur
 


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Fedora-directory-usersredhat.com
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    Re:  How to make application connect to
multi-master set-up?
  


  

     user name

     2007-02-19 10:05:00
  


  

    

  


  

    That is a viable option as well. I am always partial to using network wide solutions rather then client specific ones. We have had this problem before. Some applications are capable us talking the active backup protocal some applications are not. You get lulled into a false sence of security and you think the application is completely load balanced. Then you realized some other little app someone wrote somewhere is not configured the same way when one server goes out.


Using multiple A records is an option as well. However the failover involves making DNS changes. Based on your DNS settings that might take 20 minutes to propagate. Plus the time to actually get a DNS change through.


Load balancers and other HA solutions have a faster, sometimes almost instantanious recovery time. You manage them as a unit. There is no settings confusion. Point everythign at ldap_vip.domain.com and go. They offer niec options like 8 choices of algorithms Round robin, Weighted round robin, least connection. etc.



Edward



On 2/19/07, David Boreham < david_listboreham.org">david_listboreham.org> wrote:

Ankur Agarwal wrote:

&gt; We have a weblogic app server based application which talks to RedHat
>; LDAP through weblogic&#39;s security provider APIs.
>
> On Production env we have set-up master-master LDAP servers 
i.e. there
> are two master LDAP servers. How should i make my application connect
&gt; to these 2 servers?
&gt;
> Should there be a front-end load balancer to which my application will
> make request and then load balancer will handle requests to one of the

> LDAP servers?
&gt;
> Also note that we have weblogic cluster in Prod with 2 instances. So
> should i make each instance point to one LDAP server? But in that case
> how will automatic failover work if one of the LDAP servers go down?

&gt;
> Would be great if people can suggest any standard solution to deal
> with such situations.
>

Typically this functionality is built in to the client (or in fact the
LDAP client library).


Interposed proxies or load balancers are possible with LDAP but not
normally needed.
I&#39;m not sure about weblogic specifically but usually you get to
configure two or more
LDAP servers, or you can use multiple A records in the DNS. I'd ask BEA

-- they
should be able to tell you.





--
Fedora-directory-users mailing list
 Fedora-directory-usersredhat.com">Fedora-directory-usersredhat.com

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    Re:  How to make application connect
to	multi-master set-up?
  


  

     user name

     2007-02-19 11:17:32
  


  

    
Ankur Agarwal wrote:
>    
> We have a weblogic app server based application which
talks to RedHat LDAP through weblogic's security provider
APIs.
>    
> On Production env we have set-up master-master LDAP
servers i.e. there are two master LDAP servers. How should i
make my application connect to these 2 servers?
>    
> Should there be a front-end load balancer to which my
application will make request and then load balancer will
handle requests to one of the LDAP servers?
>    
> Also note that we have weblogic cluster in Prod with 2
instances. So should i make each instance point to one LDAP
server? But in that case how will automatic failover work if
one of the LDAP servers go down?
>    
> Would be great if people can suggest any standard
solution to deal with such situations. 
> 

If you have multiple A records for the name in DNS, the
client will 
receive all of them in a query and _can_ fail over quickly
if the first 
choice does not respond.  A lot of web browsers handle this
sensibly but 
  most other programs don't.  The way to test it is to set
up a DNS 
entry that contains one address that answers on the
application's port 
and one that doesn't and see if the application works every
time.  If 
you are writing your own client you can get failover a lot
cheaper than 
using a dedicated load balancer - and this approach also
handles 
connection failures between the client and one of the
servers that a 
load balancer would not know about.

-- 
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    lesmikesellgmail.com

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    Re:  How to make application connect to
multi-master set-up?
  


  

     user name

     2007-02-19 12:32:44
  


  

    

  


  

    Yes,

If you custom code your application you can set it up to handle multiple A records. But you need to recode your applications each application has to be reconfigured each time you add a server to the group. 

As to the cost factor. Yes buying a load balancer might cost $2000.00. you might be able to ebay one for $1000.(Linux Virtual Server is open source and GPL but that is another story.)&nbsp; How much does it really cost to recode your applications, test, and redeploy? Probably a lot more work then $2000. Our LDAP database is the corner stone of our company. We would have to recorde 10 applications to achieve our own round robin. And would only get some of the features of a hardware load balancer.



In a real world deployment more sophisticated algorithms are sometimes needed. For example say I have an older 2.0 GHZ web server and a newer 3.0 GHZ server. A more sophisticated solution has more options. For example:


Round Robin (you take one I take one)
Weighted Round Robin ; (one server better then the other, ill take 3 your take 2)
Least Connections (this server has LONG running ldap queries running on it. Send queries to the other one.)

Weighted Least connection ( This server has long running LDAP queries but it is more powerful then the other one )
Source IP ( Particular source IP is always routed to same destination server )
Least Traffic (less TCP traffic, im busy your handle this one)

Weighted Lest traffic&nbsp; (Im busy,but im alot better then you I will handle this one )

The health checking is built in at the load balancer level. If the load balancer detects a closed port that server is taken out of the group. Client applications do not need extra intelligence. When you want to upgrade a particular machine in the groop take it out of the configuration. 


Google seems to be taking a hybrid approach. They likely use GEO-DNS, mutliple A records. and hardware load balancing. Of course they are multi-datacenter. 

Non-authoritative answer:
Name: &nbsp;  
www.l.google.com
Addresses:&nbsp; 216.239.37.99, 216.239.37.104

I would be willing to bet that  216.239.37.99
 and 216.239.37.104 are hardware load balancers.

All methods are viable. It just depends on what you want. Cold Failover, High Availabilty (HA), or  Constant Availablity (CA). 


For our deployment I have a two node LDAP system (multi master) If I drop one of the nodes the IP floats to the other node within a few seconds. We did not have to recode any application, just configure them with a floating IP address. Some of our developers have built failover into their apps. I think its just extra code that there is already a proven solution to. I am a fan of mutli-master and true TCP load balancing, but thats just me. 


Edward











On 2/19/07, Les Mikesell < lesmikesellgmail.com">
lesmikesellgmail.com> wrote:
Ankur Agarwal wrote:
>;
> We have a weblogic app server based application which talks to RedHat LDAP through weblogic&#39;s security provider APIs.

&gt;
> On Production env we have set-up master-master LDAP servers i.e. there are two master LDAP servers. How should i make my application connect to these 2 servers?
&gt;
> Should there be a front-end load balancer to which my application will make request and then load balancer will handle requests to one of the LDAP servers?

>
> Also note that we have weblogic cluster in Prod with 2 instances. So should i make each instance point to one LDAP server? But in that case how will automatic failover work if one of the LDAP servers go down?

&gt;
> Would be great if people can suggest any standard solution to deal with such situations.
>

If you have multiple A records for the name in DNS, the client will
receive all of them in a query and _can_ fail over quickly if the first

choice does not respond.&nbsp; A lot of web browsers handle this sensibly but
  most other programs don't.  ;The way to test it is to set up a DNS
entry that contains one address that answers on the application's port

and one that doesn't and see if the application works every time. ; If
you are writing your own client you can get failover a lot cheaper than
using a dedicated load balancer - and this approach also handles

connection failures between the client and one of the servers that a
load balancer would not know about.

--
 &nbsp; Les Mikesell
&nbsp;   ; lesmikesellgmail.com">lesmikesellgmail.com

--

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 Fedora-directory-usersredhat.com">Fedora-directory-usersredhat.com
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