Thursday, March 01, 2007

apache proxy balancer + mongrel clusters and deploying application with capistrano

So you want to setup production server with mongrel clusters and apache proxy balancer, also wants to use capistrano for deployment, huh. Take it easy, its very simple.

You need Apache 2.2 or later on your production server, and the following ruby gems on your both machine(server and local):

* capistrano
* mongrel
* mongrel_cluster

I haven’t mentioned rails and rake gem as we are deploying a rails application so these gems are obvious.

Lets install above gems (if not installed) by issuing:

gem install --include-dependencies capistrano
gem install --include-dependencies mongrel
gem install --include-dependencies mongrel_cluster

gem install --include-dependencies capistrano gem install --include-dependencies mongrel gem install --include-dependencies mongrel_cluster

Now make sure that the following modules are enabled (they are disabled by default) :

* mod-rewrite
* mod-proxy
* mod-proxy-http
* mod-proxy-balancer

to check if they are enabled issue ” /etc/init.d/apachectl -M ” on server, it will list all the enabled modules. For Debian systems all enabled modules are in /etc/apache2/mods-enabled directory and all available modules are in /etc/apache2/mods-available directory, to enable them issue ” a2enmod MOD_NAME “.

Now create the production database(on server) and update database.yml for production database settings.

After this configure mongrel by issuing ” mongrel_rails cluster::configure -e production -p 8000 -a -N 2 -c ./ ” inside the rails application root directory(on client machine). This will create mongrel_cluster.yml in config directory. You can change parameters in this command, as -p 8000 specifies that mongrel instances will start up on port number starting 8000, -a specifies that mongrel instances will listen to the localhost, -N specifies the number of mongrel instances and -c specifies the rails root directory.

Now its time to capistranize rails application, issue ” cap –apply-to ./ APP_NAME ” inside rails application root directory(on client machine), this will add two files(config/deploy.rb and lib/tasks/capistrano.rake) to the rails application. Edit deploy.rb according to your requirements. Also add the following code to deploy.rb :
view plainprint?

task :restart, :roles => :app do
# stop mongrel clusters for previous release and start for current
run "cd #{previous_release} && mongrel_rails cluster::stop"
run "sleep 5"
run "cd #{current_release} && mongrel_rails cluster::start"

Now on your local machine issue these two commands in only once ” rake remote:setup ” and ” rake remote:cold_deploy “, when you issue ” rake remote:setup ” it will prompt for the server password and create necessary directories on the server and ” rake remote:cold_deploy ” will deploy your code to the server. Next time whenever you want to deploy to the server you just need to issue ” rake remote:deploy ” not ” rake remote:cold_deploy “.

Now we are just one step back, we need to configure apache proxy balancer for mongrel instances. Add the following code to the httpd.conf file:
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<Proxy balancer://mongrel_cluster>

<VirtualHost *:8080>
DocumentRoot /Users/yu/Sites/RubyOnRails

<Directory "/Users/yu/Sites/RubyOnRails">
Options FollowSymLinks
AllowOverride All
Order allow,deny
Allow from all

RewriteEngine On

RewriteCond %{DOCUMENT_ROOT}/system/maintenance.html -f
RewriteCond %{SCRIPT_FILENAME} !maintenance.html
RewriteRule ^.*$ /system/maintenance.html [L]

RewriteRule ^/$ /index.html [QSA]
# Rewrite to check for Rails cached page
RewriteRule ^([^.]+)$ $1.html [QSA]

RewriteRule ^/(.*)$ balancer://mongrel_cluster%{REQUEST_URI} [P,QSA,L]

you need to change the above code according to you requirement. Also you need to restart apache server by issuing ” /etc/init.d/apachectl restart “. Now you are done.

But we also need to add a script to start mongrel instances when the server restarts, otherwise whenever the server restart there will no mongrel instance running.

Just create a file named mongrel_clusters (you can choose any name) in /etc/init.d directory with the following code:
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1. #!/bin/bash
2. #
3. # chkconfig: 345 94 16
4. # description: Startup script for mongrel
5. BASEDIR=/var/www/your_app
6. export HZ=100
7. export TERM=linux
8. export SHELL=/bin/bash
10. export USER=root
11. export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/bin/X11:/usr/local/bin:/usr/bin:/bin:/usr/bin/X11:/usr/games
12. export MAIL=/var/mail/root
13. export _=/usr/bin/env
14. export PWD=/etc/init.d
15. export HOME=/root
16. export SHLVL=2
17. export LOGNAME=root
19. cd $BASEDIR
20. case "$1" in
21. start)
22. echo "starting up mongrel in $BASEDIR"
23. mongrel_rails cluster::start
24. ;;
25. stop)
26. echo "stopping mongrel"
27. mongrel_rails cluster::stop
28. ;;
29. restart)
30. mongrel_rails cluser::stop
31. sleep 3
32. mongrel_rails cluster::start
33. ;;
34. esac

You need to change the BASEDIR in the above code. Make this file executable by ” chmod +x /etc/init.d/mongrel_clusters ”
Issue these commands to add this script at system startup:

Debian: /usr/sbin/update-rc.d /etc/init.d/mongrel_clusters defaults
RedHat: /usr/sbin/chkconfig –add /etc/init.d/mongrel_clusters and /usr/sbin/chkconfig –level 2 /etc/init.d/mongrel_clusters on

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