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Capistrano + Nginx + Thin deployment on Linode

November 10, 2009 6 comments

This was long lost post I had written about 8 months ago (converted from wiki to HTML – so pardon typos if any)

Terminologies

Capistrano is a ruby gem which helps in remote deployment. As against widely known convention, Capistrano can be used for any deployment, not just a rails app!

Nginx is a web-proxy server. This is simply a light weight HTTP web-server which received requests on HTTP and passes them to other applications. This is way more preferable than Application servers like Apache! Moreover, nginx is very easily configurable and can support multiple domain-names very easily. It has an in-build load-balancer which can send requests to apps based on its internal load-balancing mechanism.

Thin is the next-generation lean, mean rails server. Its much faster, lighter in memory than mongrel. Its has an internal event based mechanism for request processing and a very high concurrency performance ratio than other rails servers.

Linode is a VPS (a Virtual Private Server) that is hosted by www.linode.com. As the name suggests ;), its a “Linux Node”.  We are using Ubuntu 8.10 (Tip: To find Ubuntu release, issue command: lsb_release -a) NOTE: In the linode we had, it was a raw machine with no packages installed. Please read Linode RoR package installation for details.

Steps

Capistrano Configuration Follow the steps provided by Capistrano for basic instructions: Capistrano – From The Beginning Some modifications that you may need (as I needed for deployment):

  • Edit Capfile and add the following to it. This ensures that remote capistrano deployment does not fork a remote shell using command “sh -c”. Some hosting servers do not allow remote shells.
  • default_run_options[:shell] = false
  • In addition to changes mentioned in Capistrano tutorial, add the following to config/deploy.rb. This ensures that “sudo” is not used (default for Capistrano) and the user is “root”. Not usually a good practice.. but what the hell!
  • set :use_sudo, false            set :user, "root"
  • Since capistrano uses default script/spin and script/process/reaper, we need to override the deploy:start, deploy:stop and deploy:restart to ensure that we can start/stop the thin service and the ferret_server. I know that in deply:restart, there is a copy-paste involved but I am trying to find out how to invoke a rake task from another rake task.
namespace :deploy do
    desc "Custom AceMoney deployment: stop."
    task :stop, :roles => :app do

        invoke_command "cd #{current_path};./script/ferret_server -e production stop"
        invoke_command "service thin stop"
    end

    desc "Custom AceMoney deployment: start."
    task :start, :roles => :app do

        invoke_command "cd #{current_path};./script/ferret_server -e production start"
        invoke_command "service thin start"
    end

    # Need to define this restart ALSO as 'cap deploy' uses it
    # (Gautam) I dont know how to call tasks within tasks.
    desc "Custom AceMoney deployment: restart."
    task :restart, :roles => :app do

        invoke_command "cd #{current_path};./script/ferret_server -e production stop"
        invoke_command "service thin stop"
        invoke_command "cd #{current_path};./script/ferret_server -e production start"
        invoke_command "service thin start"
    end
end

Thin Configuraion I looked up most of the default configuration of Thin and Nginx on Ubunto at Nginx + Thin. Some extra configuration or differences are mentioned below.

  • The init script for starting thin and nginx during startup is configured during package installation. Leave them as they are.
  • The following command generates the /etc/thin/acemoney.yml for 3 server starting from port 3000. Note that the -c option specifies the BASEDIR of the rails app. Do NOT change any settings in this file as far as possible.
  • thin config -C /etc/thin/acemoney.yml -c /home/josh/current --servers 3 -e production -p 3000
  • Starting and stopping thin is as simple as
  • service thin start
    service thin stop
  • This will read the acemoney.yml file and spawn the 3 thin processes. I noticed that each thin server took about 31MB in memory to start with and with caching went upto ~70MB. On the contrary, a mongrel server (tested earlier) started with 31MB but exceeded 110MB later!

Nginx Configuration Installation on nginx is simple on Ubuntu 😉

apt-get install nginx

Configure the base /etc/nginx/nginx.conf. The default configuration are fine but I added / edited a few more for as recommended at Nginx Configuration

        worker_processes  4;

        gzip_comp_level 2;
        gzip_proxied any;
        gzip_types  text/plain text/html text/css application/x-javascript
                    text/xml application/xml application/xml+rss text/javascript;

According to this configuration above, nginx will spawn 4 worker threads and each worker thread can process 1024 connections (default setting). So, nginx can now process ~4000 concurrent HTTP requests !!! See performance article of thin at Thin Server

Configure the domainname, in our case acemoney.in. Ensure that acemoney.in “A record” entry points to this server! Check this by doing a nslookup or a ping for the server. In /etc/nginx/sites-available create a file by the domainname to be hosted. So I added /etc/nginx/sites-available/acemoney.in. In /etc/nginx/sites-enabled create a symbolic link to this file.

ln -s /etc/nginx/sites-available/acemoney.in /etc/nginx/sites-enabled/acemoney.in 

Now add the contents in /etc/nginx/sites-available/acemoney.in This is the key configuration to hook up nginx with thin.

upstream thin {
     server 127.0.0.1:3000;
     server 127.0.0.1:3001;
     server 127.0.0.1:3002;
}

server {
    listen 80;
    server_name acemoney.in;

    root /home/josh/current/public;

    location / {
      proxy_set_header X-Real-IP $remote_addr;
      proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
      proxy_set_header Host $http_host;
      proxy_redirect false;

      if (-f $request_filename/index.html) {
        rewrite (.*) $1/index.html break;
      }
      if (-f $request_filename.html) {
        rewrite (.*) $1.html break;
      }
      if (!-f $request_filename) {
        proxy_pass http://thin;
        break;
      }
    }

    error_page 500 502 503 504 /50x.html;
    location = /50x.html {
      root html;
    }
}

To analyze this configuration, here are some details:

The following lines tell nginx to listen on port 80 for HTTP requests to acemoney.in. The ‘root’ is the public directory for our rails app deployed at /home/josh/current!

server {
    listen 80;
    server_name acemoney.in;

    root /home/josh/current/public;

Now, nginx will try to process all HTTP requests and try to give the response.. for static HTML’s it will automatically give the data from the ‘root’. If it cannot find the HTML file, it will ‘proxy_pass’ it to thin. “thin” in the code below is an ‘upstream’ directive that tells nginx where to forward the current request it cannot directly serve.

if (!-f $request_filename) {
        proxy_pass http://thin;
        break;
      }

The upstream code is where load-balancing plays a role in nginx. The following code tells nginx which all processes are running on which different ports and it forwards requests to any of the servers based on its internal load balancing algorithm. The servers can be on different machines (i.e. different IP addresses) if needed. In AceMoney, we have started 3 thin servers on 3 different ports!

upstream thin {
     server 127.0.0.1:3000;
     server 127.0.0.1:3001;
     server 127.0.0.1:3002;
}

Performance Statistics Nothing is complete without them. Here is what I found out for 3 thin servers and 1 ferret_server.

top - 14:06:10 up 7 days, 22:58,  2 users,  load average: 0.00, 0.00, 0.00
Tasks:  84 total,   1 running,  83 sleeping,   0 stopped,   0 zombie
Cpu0  :  0.0%us,  0.0%sy,  0.0%ni,100.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu1  :  0.0%us,  0.0%sy,  0.0%ni,100.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu2  :  0.0%us,  0.0%sy,  0.0%ni,100.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu3  :  0.0%us,  0.0%sy,  0.0%ni,100.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:    553176k total,   530868k used,    22308k free,    16196k buffers
Swap:   524280k total,     2520k used,   521760k free,    87280k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
12424 mysql     18   0  127m  42m 5520 S    0  7.9   0:23.01 mysqld
18338 root      15   0 77572  70m 4392 S    0 13.1   0:06.79 thin
18348 root      15   0 71176  64m 4388 S    0 11.9   0:06.51 thin
18343 root      15   0 68964  62m 4384 S    0 11.5   0:07.20 thin
18375 root      18   0 70912  54m 2660 S    0 10.0   2:34.24 ruby
 8141 www-data  15   0  5176 1736  820 S    0  0.3   0:00.07 nginx
 8142 www-data  15   0  5176 1724  816 S    0  0.3   0:00.01 nginx
 8144 www-data  15   0  5152 1720  816 S    0  0.3   0:00.06 nginx
 8143 www-data  15   0  5156 1656  784 S    0  0.3   0:00.00 nginx

As can be seen:

  • Each thin server takes around 70M
  • The Mysql server takes 41M
  • Ruby process (18375 above) is the ferret_serve which takes 54M
  • 4 nginx threads take about 1.7K in memory.
 Overall: (3 thin server cluster + Mysql + ferret): 300MB