Monday, May 4, 2009

Creating a Private Ruby Gem Server

While installing a new ruby gem in a machine,we normally use the gem install <gem name> command.This command downloads the latest version of a particular gem.The problem is that ROR gems are not always backward compatible.So if a ROR application was developed using a particular version of a gem (Ex:0.1.1) and the latest version of the gem in the internet (normally is 0.1.2,problem may arise if the version 0.1.2 is not backward compatible with version 0.1.1.This may cause a serious trouble when the application is deployed into the web server and the wrong version of the gem is installed.Most probably the application will not function as expected.

A solution to this problem is to deploy the exact version of all the gems those were used during development.One way to implement this is hosting the correct version of the gems into a web server(thus call it a private gem server).I have tested this option in a Apache web server.The steps are as follows:

1.Create a directory for hosting gems on the public files area of the web server.Let's refer is as <Base Directory>.

ssh user@web.server
cd /var/www
mkdir my_gem_server

2.Create a sub directory called "gems" under the <Base Directory>.The name of the sub directory must be "gems" by convention.

ssh user@web.server
cd /var/www/my_gem_server
mkdir gems

3.Copy all the necessary gems from the development machine into the /var/www/my_gem_server/gems sub directory.

4.Generate the gem index:

gem comes with a command generate_index which generates all of the files necessary for serving gems over HTTP.Run this command into the <Base Directory> (/var/www/my_gem_server).

gem generate_index -d /var/www/my_gem_server

Now the private gem server is ready to serve the gems for download and install.

To install the private gems into the target web server where the ROR application will be deployed,log in and run the following command.

gem install <gem name> --source http://<private gem server>/<Base Directory>

The correct version of the gems will be installed and thus the application integrity will be maintained.We need to rerun the gem generate_index command each time we add or remove a gem from the private gem server.

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