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Deployment of Ruby on Rails applications on OpenBSD

Published by alex.shapovalov on April 5, 2010 under openBSD, ruby  

Preamble

In this post I will define typical production environment on OpenBSD OS for deployment of Ruby on Rails applications.

There are few common things:
1. The Ruby on Rails framework doesn’t support concurrent running in multiple threads within the same process, and so to scale it and fully utilize available hardware we need to execute application in several processes.
2. We need load-balancer to spread incoming requests between application instances.
3. We need separate web-server to serve static content.

Overall configuration

At first all incoming HTTP requests from a clients come to httpd web-server, it servers all static content, and send other requests to HAProxy.
HAProxy receives requests and selects free Thin instance, forwards the request to it, receives a response and passes it back to httpd.

Following diagram should give you basic understanding about common work of components :
deployment diagram

OpenBSD Httpd – standard OpenBSD web-server

I suggest OpenBSD standard web-server as you can find it as part of OpenBSD base installation, it checked for security issues and being updated as part of OpenBSD. We will use it to serve static content and don’t bother our Thin servers.

file: httpd.conf

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BindAddress SERVER_IP_ADDRESS

# Dynamic Shared Object (DSO) Support
# caching proxy
LoadModule proxy_module /usr/lib/apache/modules/libproxy.so

# allow Symbolic Links for root of our static content and all sub-directories

Options +FollowSymLinks
ServerAdmin ADMIN_EMAIL

# path to root of our static content
DocumentRoot /var/www/railsdocs/RAILS_PROJECT/public
ServerName SERVER_NAME
ServerAlias www.SERVER_NAME

# directories that contain static content (they excluded from dispatching to HAProxy)
ProxyPass /images !
ProxyPass /stylesheets !
ProxyPass /javascripts !
ProxyPass /500.html !
ProxyPass /503.html !

# address where to send and from receive requests (HAProxy listens that address)
ProxyPass / http://127.0.0.1:4000/
ProxyPassReverse / http://127.0.0.1:4000/

# Disallows remote servers to be mapped into the space of the local server.
ProxyRequests Off

# Don't use incoming Host HTTP request header for proxy request.
ProxyPreserveHost Off

ErrorLog logs/SERVER_NAME-error_log
CustomLog logs/SERVER_NAME-access_log common

see for configuration details: man httpd

For OpenBSD 4.6/4.6 -Stable
It’s the hard part, OpenBSD4.6 has a bug in mod_proxy module so ‘!’ directive doesn’t work.
You have to edit following file: /usr/src/usr.sbin/httpd/src/modules/proxy/mod_proxy.c

Find method: static int proxy_trans(request_rec *r)
in that method after condition: if (len > 0) {
add 2 string:

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if (ent[i].real[0] == '!' && ent[i].real[1] == '\0')
return DECLINED;

so final part of code:

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if (len > 0) {
if (ent[i].real[0] == '!' && ent[i].real[1] == '\0')
return DECLINED;

Then recompile your system, it’s common procedure for following -stable so you should already know it otherwise see for details for building instructions: http://www.openbsd.org/faq/faq5.html

Thin – high performance ruby web server

We need some Ruby web-server, and it seems that at this time Thin provides best performance.
At least we see such results on Thin homepage: http://code.macournoyer.com/thin/

file: start.sh

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# start work instances
thin start -C thin-production.yml

file: thin-production.yml

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---
environment
: production

port
: 4001
address
: 127.0.0.1
daemonize
: true
servers
: 4

chdir
: /var/www/railsdocs/RAILS_PROJECT
pid
: tmp/pids/thin.pid
log
: log/thin.log

user
: myuser
group
: mygroup

require
: []

see for configuration details: http://code.macournoyer.com/thin/usage/

HAproxy – TCP/ HTTP load balancer

As Rails doesn’t support concurrent running each incoming request should be assigned to a separate process. HAProxy can be configured to send only one request at a time to every Thin server, it will always pick instance that is not busy with something.

It provides bunch of other useful things like:
– route HTTP requests depending on statically assigned cookies ;
– switch to backup servers in the event a main one fails ;
– accept connections to special ports dedicated to service monitoring ;
– add/modify/delete HTTP headers both ways ;
– block requests matching a particular pattern ;
for full documentation see: http://haproxy.1wt.eu/#docs

note:
If someone thinks that we could use nginx for that purpose check following performance comparison of HAProxy and Nginx:
http://affectioncode.wordpress.com/2008/06/28/another-comparison-of-haproxy-and-nginx/

file: haproxy.cfg

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defaults
log     global
mode    http

# provides more detailed information about HTTP contents, such as the request and some cookies
option  httplog
# do not to log any session which didn't transfer any data
option  dontlognull
# allow the proxy to break their persistence and redistribute connections in case of failure
option  redispatch

# the number of attempts to reconnect after a connection failure to a server
retries 3

# the time we accept to wait for a connection to establish on a server
contimeout      100000
# the time we accept to wait for data from the client, or for the client to accept data
clitimeout      100000
# the time we accept to wait for data from the server, or for the server to accept data
srvtimeout      100000

listen project_proxy 127.0.0.1:4000
balance roundrobin

# creates an HTTP 'X-Forwarded-For' header which contains the client's IP address.
# This is useful to let the final web server know what the client address was
option forwardfor

# using “maxconn 1″ improves performance with Rails.
# As Rails instance can process only 1 request “maxconn 1″ force HAProxy to select next free instance

server  app1_1 127.0.0.1:4001 check inter 60000 rise 2 fall 5 maxconn 1
server  app1_2 127.0.0.1:4002 check inter 60000 rise 2 fall 5 maxconn 1
server  app1_3 127.0.0.1:4003 check inter 60000 rise 2 fall 5 maxconn 1
server  app1_4 127.0.0.1:4004 check inter 60000 rise 2 fall 5 maxconn 1

# httpd web-server will handle it in case of 503, 504 errors due to it's static content
errorloc    503  http://DOMAIN_NAME/503.html
errorloc    504  http://DOMAIN_NAME/504.html

# statistics page thru http://127.0.0.1:8080
listen stats 127.0.0.1:8080
balance roundrobin
mode http
stats uri   /

see for configuration details: http://haproxy.1wt.eu/#docs

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4 Responses to “Deployment of Ruby on Rails applications on OpenBSD”

  1. Sohan says:

    Your post has been linked at the Drink Rails blog.

  2. alex.shapovalov says:

    Thank you Sohan.

  3. Paul says:

    thanks a lot!Well post!!

  4. chrismartin says:

    nice very useful

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