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DevOps on EC2 using Capistrano

DevOps is the combination of development and operation processes. Cloud with your DevOps offers some fantastic properties. The ability to leverage all the advancements made in software development around repeatability and testability with your infrastructure. The ability to scale up as need be real time and among other things being able to harness the power of self healing systems.

The process piece of devops is about taking the principles behind Agile to the entire continuous software development process. The obvious step is bringing Agile ideas to the operations team, which is sorely needed. Traditionally in the enterprise, the application development team is in charge of gathering business requirements for a software program and writing code. The development team tests their program in an isolated development environment for quality assurance which is later handed over to the operations team. The operations team is tasked with deploying and maintaining the program. The problem with this paradigm is that when the two teams work separately, the development team may not be aware of operational roadblocks that prevent the program from working as anticipated.

Capistrano

Capistrano is a developer tool for running scripts on multiple servers, mainly used for deploying web applications on to the servers. It is typically installed on a workstation, and used to deploy code from your source code management to one, or more servers. Capistrano is originally called “SwitchTower”, the name was changed to Capistrano in March 2006 because of some trademark conflict. It is a time saving command line tool and it is very useful to AWS/EC2 servers because we can deploy the code to 1000’s of aws servers by using a single command. For the security of servers we are commonly using aws ssh key authentication. In capistrano  we use this aws ssh key to deploy the web applications to the aws servers.

In Cloud Computing, deploying applications to production/live servers is always a delicate task. The whole process needs to be quick to minimize downtime. Automating the deployment process helps running repetitive tasks minimizing the possibility human error. It is also a good idea to have a proven and easy way to rollback to a previous version if something goes wrong.

It is a standalone utility that can also integrate nicely with Rails. We simply provide Capistrano with a deployment “recipe” or “formula” that describes our various servers and their roles. It is a single-command deployment. it even allows us to roll a bad version out of production and it revert back to the previous release very easily.

Capistrano Deployment

The main functionality of the Capistrano is to Deploy the rails application which we have already developed and we are using the “SVN” or “GIT” to manage the code. It will transfer all the files of our rails application which we have developed in our local host to aws servers directly by simply executing a simple command in our command prompt.

 

Steps to deploy a rails application

gem install capistrano

Now,we need to capistranize our rails application using the following commands

capify .

It will create two files


config/deploy.rb
capfile .

How to set up deploy.rb file


require ‘rubygems'
require 'activesupport'
set :application, "<application name>"
set :scm_username/ "<username>"
set :use_sudo, false
set :repository, "http://#{scm_username}@www.example.com/svn/trunk"
set :deploy_to, "/var/www/#{application}"
set :deploy_via, :checkout
set :scm, :git
set :user, "root"
role :app, "<domain_name>"
role :web, "<domain_name>"
rold :db, "<domain_name>", :primary => true
namespace :migrations do
desc "Run the Migrations"
task :up, :roles => :app do
run "cd #{current_path}; rake db:auto:migrate;"
end
task :down, :roles => :app do
run "cd #{current_path}; rake db:drop; rake
db:create"
end
end

where,

scm_username’ is your user name
application’ is an arbitrary name you create to identify your application on the server
use_sudo’ specifies to capistrano that it does not need to append ‘sudo’ before all the commands it will run
repository’ identifies where your subversion repository is located

If we aren’t deploying to server’s default path, we need to specify the actual location by using the ‘deploy_to’ variable as given below

set :deploy_to, "/var/www/#{application}"
set :deploy_via, :checkout

If we are using the git to manage our source code, specify the SCM by using the ‘scm’ variable as given below

set :scm, :git
set :user, "root"
role :app, "<domain_name>"
role :web, "<domain_name>"
rold :db, "<domain_name>", :primary => true

Since most rails users will have the same domain name for their web,app and database, we can simply use our domain variable we set earlier.

namespace :migrations do
desc "Run the Migrations"
task :up, :roles => :app do
run "cd #{current_path}; rake db:auto:migrate;"
end
task :down, :roles => :app do
run "cd #{current_path}; rake db:drop; rake
db:create"
end
end

After completion of our settings in the deploy.rb file, we need to commit the application by using “svn commit” command if we use svn.

Then we need to run the following command:


cap deploy:setup

It is used to create the directory structure in server.

cap deploy:check

It checks all the dependencies/things like directory permission and necessary utilities to deploy the application by using capistrano.

If everything is successful, you should see a message like:
You appear to have all necessary dependencies installed
And finally deploy the application by using the following command:

cap deploy

Command finished successfully

To Clean up the releases directory, leaving the five most recent releases

Cap cleanup

Prints the difference between what was last deployed, and what is currently in our repository

cap diff_from_last_deploy

To Rolls back to the previously deployed version

cap deploy:rollback:code

Amazon’s EC2 cloud cuts the requisition time of the order & delivery stages down to just minutes. This is already a 75% savings in deployment time! But, without automated deployment, you’ll still need a week to get your application installed.

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