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14/06/2007, 17h11

"Laura" <f.marchioni@pride.it> wrote in message
news:1181809154.589891.176360@j4g2000prf.googlegro ups.com...
> Hi all !
> We have a web application that is hosted on Apache HTTP server.
>
> Now we decided to make the application more scalable so we'll replace
> the single Apache server with a farm of 3 Apache Servers.
>
> So now I need to load-balance the client requests between the 3
> Apache Servers.
>
> Is it enough if I configure DNS round-robin so that, given a domain
> name, it will distribute the load between servers ?

In general this will give you (loose) load balancing.

> The main problem
> is that I don't know if DNS round robin is able to use session
> affinity, so that calls from one IP address are routed always to the
> same Apache server. (If not HTTP session state will be lost.....)

No, Round Robin will NOT do that but normally this you will get
something like this due to requesting DNS Server and requesting
DNS clients caching the results.

E.g., a client gets a resolution from your server (perhaps indirectly
from the client's own DNS server) and tends to keep that result
in cache at both the client and the server (for modern Windows
clients and practically all DNS servers anyway.)

> If not, can you point out other alternatives ? (Hardware load-
> balancer?)

NLB from Microsoft is built into the product (you must add/configure
it.)

NLB (Network Load Balancing) provides load balancing, explicit
affinity on either a single IP or Class-C basis, and also offers fault
tolerance.

Round Robin does NOT provide for fault tolerance.

> By the way, the farm of Apache Servers runs on a Windows Server Box.

You should also question a design that requires such affinity. Normally
all state data for such clients should be stored on a backend database
(perhaps with Server Clustering) OR on the web clients (e.g., using
).

--
Herb Martin, MCSE, MVP
http://www.LearnQuick.Com
(phone on web site)

14/06/2007, 17h11	#3
Herb Martin Messages: n/a Hébergeur:	Re: DNS round robin and Apache Server "Laura" <f.marchioni@pride.it> wrote in message news:1181809154.589891.176360@j4g2000prf.googlegro ups.com... > Hi all ! > We have a web application that is hosted on Apache HTTP server. > > Now we decided to make the application more scalable so we'll replace > the single Apache server with a farm of 3 Apache Servers. > > So now I need to load-balance the client requests between the 3 > Apache Servers. > > Is it enough if I configure DNS round-robin so that, given a domain > name, it will distribute the load between servers ? In general this will give you (loose) load balancing. > The main problem > is that I don't know if DNS round robin is able to use session > affinity, so that calls from one IP address are routed always to the > same Apache server. (If not HTTP session state will be lost.....) No, Round Robin will NOT do that but normally this you will get something like this due to requesting DNS Server and requesting DNS clients caching the results. E.g., a client gets a resolution from your server (perhaps indirectly from the client's own DNS server) and tends to keep that result in cache at both the client and the server (for modern Windows clients and practically all DNS servers anyway.) > If not, can you point out other alternatives ? (Hardware load- > balancer?) NLB from Microsoft is built into the product (you must add/configure it.) NLB (Network Load Balancing) provides load balancing, explicit affinity on either a single IP or Class-C basis, and also offers fault tolerance. Round Robin does NOT provide for fault tolerance. > By the way, the farm of Apache Servers runs on a Windows Server Box. You should also question a design that requires such affinity. Normally all state data for such clients should be stored on a backend database (perhaps with Server Clustering) OR on the web clients (e.g., using ). -- Herb Martin, MCSE, MVP http://www.LearnQuick.Com (phone on web site)