Re: [users@httpd] help needed on Load balancing and environment variables scope

chalu <chalu@xxxxxxxxxxx> · Wed, 25 May 2005 13:35:29 -0400

Andrea wrote:

Hy everybody,

I'm configuring Apache as a reverse proxy and I am doing loadbalancing 

between some backend servers.

I' am doing load balancing using mod_rewrite. My backend webapps 

(every webapp is replicated in various servers) use cookies to mantain 

sessions.

So my goal was to redirect every user to same server he first was 

redirected to.

I achieved this setting the environment variable SERVER to the server 

name the user is first redirected to, then storing this value in a 

cookie; all the following request of the same user are then redirected 

to the server whose name is stored in the "backend_server" cookie.

 My question is:

what is the scope of the SERVER environment variable ? What happens if 

many users request simultaneusly ? Does the value of SERVER is shared 

inconsistently ?

I mean...may a user be redirected to the wrong server ?

Below I enclose the my config.

Any help is really appreciated.

Thanks
Andrea

RewriteMap lb rnd:/usr/local/apache2/conf/backend.table

RewriteCond %{HTTP_COOKIE} (^|(.+;)*)backend_server=(.+)(;?)

RewriteRule ^/s1_webconsole/(.*)$  http://%3/webconsole/$1 

[E=SERVER:%3,P,L] 

RewriteCond %{HTTP_COOKIE} !(^|(.+;)*)backend_server=(.+)(;?)

RewriteRule ^/s1_webconsole/(.*)$  to://${lb:www}/$1

RewriteRule ^to://([^/]+)/(.*)$  http://$1/$2 [E=SERVER:$1,P,L] 

<Location /s1_webconsole>

...
Header add Set-Cookie backend_server=%{SERVER}e;Path=/s1_webconsole
 ...
</Location>

Why not use "pound"?

Andrea wrote:

> Hy everybody,
> I'm configuring Apache as a reverse proxy and I am doing loadbalancing 
> between some backend servers.
> I' am doing load balancing using mod_rewrite. My backend webapps 
> (every webapp is replicated in various servers) use cookies to mantain 
> sessions.
>  
> So my goal was to redirect every user to same server he first was 
> redirected to.
> I achieved this setting the environment variable SERVER to the server 
> name the user is first redirected to, then storing this value in a 
> cookie; all the following request of the same user are then redirected 
> to the server whose name is stored in the "backend_server" cookie.
>  
>  My question is:
> what is the scope of the SERVER environment variable ? What happens if 
> many users request simultaneusly ? Does the value of SERVER is shared 
> inconsistently ?
> I mean...may a user be redirected to the wrong server ?
>  
> Below I enclose the my config.
>  
> Any help is really appreciated.
> Thanks
> Andrea
>  
>  
> RewriteMap lb rnd:/usr/local/apache2/conf/backend.table
> RewriteCond %{HTTP_COOKIE} (^|(.+;)*)backend_server=(.+)(;?)
> RewriteRule ^/s1_webconsole/(.*)$  http://%3/webconsole/$1 
> [E=SERVER:%3,P,L] 
> RewriteCond %{HTTP_COOKIE} !(^|(.+;)*)backend_server=(.+)(;?)
> RewriteRule ^/s1_webconsole/(.*)$  to://${lb:www}/$1
> RewriteRule ^to://([^/]+)/(.*)$  http://$1/$2 [E=SERVER:$1,P,L] 
>  
> <Location /s1_webconsole>
> ...
> Header add Set-Cookie backend_server=%{SERVER}e;Path=/s1_webconsole
>  ...
> </Location>

Why not use "pound"?

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