These are instructions for setting up session affinity with Nginx web server and Plone CMS. Nginx can be used as a load balancer at the front of several Plone front-end processes (ZEO processes). By default, Nginx does not do session affinity, a.k.a. sticky sessions.  If you have site functionality which stores user specific data on the front end session data, let’s say an eCommerce site shopping cart, you must always redirect the user to the same ZEO process or they will have have different random shopping cart for each front end client.

Instructions assume you are installing Nginx via buildout.

Nginx sticky session can be loaded from here

• Nginx sticky sessions module

Manually extract nginx-sticky-module under src folder:

cd src
wget http://nginx-sticky-module.googlecode.com/files/nginx-sticky-module-1.0-rc2.tar.gz

Then add it do Nginx configure options in buildout part:

[nginx-build]
recipe = zc.recipe.cmmi
url = http://sysoev.ru/nginx/nginx-0.7.65.tar.gz
extra_options = --add-module=${buildout:directory}/src/nginx-sticky-module-1.0-rc2

Now test recompling Nginx via buildout:

mv parts/nginx-build/ parts/nginx-build-old # Make sure full rebuild is done
bin/buildout install nginx-build

See that it compiles without erros. Here is the line of compiling sticky module:

gcc -c -O -pipe  -O -W -Wall -Wpointer-arith -Wno-unused-parameter -Wunused-function -Wunused-variable -Wunused-value -Werror -g   -I src/core -I src/event -I src/event/modules -I src/os/unix -I objs -I src/http -I src/http/modules -I src/mail \
        -o objs/addon/nginx-sticky-module-1.0-rc2/ngx_http_sticky_module.o \

Now add sticky to the load balancer section of nginx config:

[balancer]
recipe = gocept.nginx
nginx = nginx-build
...
http {
        client_max_body_size 64M;
        upstream zope {
                sticky;
                server ${hosts:client1}:${ports:client1} max_fails=3 fail_timeout=30s;
                server ${hosts:client2}:${ports:client2} max_fails=3 fail_timeout=30s;
                server ${hosts:client3}:${ports:client3} max_fails=3 fail_timeout=30s;
        }

Reinstall nginx balaner configs and start-up scripts:

bin/buildout install balancer

See that generated configuration is ok:

bin/nginx-balancer configtest

Restart Nginx:

bin/nginx-balancer stop ;bin/nginx-balancer start

Check that some (non-anonymous) page has route cookie set by sticky module:

Huiske-iMac:tmp moo$ wget -S http://yoursite.com/sisalto/secret-travel-destination-infoa
--2011-03-21 21:31:40--  http://yoursite.com/sisalto/secret-travel-destination-infoa
Resolving yoursite.com (yoursite.com)... 12.12.12.12
Connecting to yoursite.com (yoursite.com)|12.12.12.12|:80... connected.
HTTP request sent, awaiting response...
  HTTP/1.1 200 OK
  Server: nginx/0.7.65
  Content-Type: text/html;charset=utf-8
  Set-Cookie: route=7136de9c531fcda112f24c3f32c3f52f
  Content-Language: fi
  Expires: Sat, 1 Jan 2000 00:00:00 GMT
  Set-Cookie: I18N_LANGUAGE="fi"; Path=/
  Content-Length: 41471
  Date: Mon, 21 Mar 2011 19:31:40 GMT
  X-Varnish: 1979481774
  Age: 0
  Via: 1.1 varnish
  Connection: keep-alive

Now test it by doing manual session related activity and see that your shopping cart is not “lost”.

More info

• http://code.google.com/p/nginx-sticky-module/source/browse/trunk/README
• http://nathanvangheem.com/news/nginx-with-built-in-load-balancing-and-caching

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