Programmer Notes

Capistrano is a tool used for remote server automation and deployment, written in Ruby. It uses SSH to connect with server for performing various operations and Rake to define tasks required to perform deployment on a specific server. To automate repetitive deployment tasks, it can also be used for any language or framework including Java, PHP, Rails, etc.

Additionally, you can write your own automated deployment scripts by writing rake tasks. However, Capistrano provides a basic structure for multiple plugins to deploy them easily. Following is it’s file structure:

├── Capfile
├── config
│   ├── deploy
│   │   ├── production.rb
│   │   └── staging.rb
│   └── deploy.rb
└── lib
    └── capistrano
            └── tasks

Here, Capfile is used to require plugin files and define user defined rake tasks. Config/Deploy is a directory where environment (staging/production) specific files are placed for the server. Deploy.rb file is used to define generic variables, configurations, and tasks, etc. Additionally, Lib/Capistrano/Tasks is a directory where user defined custom rake tasks for capistrano are placed.

Setup in Ruby on Rails

In a project’s Gemfile, specify “capistrano” as a core gem and any other gem like “capistrano-rails” to provide extended core functionality.

To add extra functionality in Capfile, “capistrano-rails” gem is required here. Add the following line of code to import the required gem:

To create capistrano recipe in deploy.rb file, set the following variables used by capistrano for all environments:

To create capistrano recipe in config/deploy/production.rb file, set environment specific variables (production in the following case):

Here, “serverIP_or_domain” is the IP address or domain name that the client machine uses to connect with server and for its deployment.

Tasks that are shared among all environments are placed in deploy.rb file like variables while environment specific tasks are placed in their respective environment files (for example, tasks of production environment will be placed in config/deploy/production.rb file).

The following two tasks are presented as an example of rake tasks having Capistrano DSL support.

1. This example is used for checking the access to a specified server.
   
   desc "Check that we can access specified server" task :check_write_permissions do on roles(:all) do |host| if test("[ -w #{fetch(:deploy_to)} ]") info "#{fetch(:deploy_to)} is writable on #{host}" else error "#{fetch(:deploy_to)} is not writable on #{host}" exit end end end

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   desc "Check that we can access specified server" task :check_write_permissions do   on roles(:all) do |host|     if test("[ -w #{fetch(:deploy_to)} ]")       info "#{fetch(:deploy_to)} is writable on #{host}"     else       error "#{fetch(:deploy_to)} is not writable on #{host}"       exit     end   end end

2. The example is used for checking whether Git local branch is synced with remote branch or not.
   
   desc "checks whether local git is in sync with remote" task :check_is_repo_updated do on roles(:web) do |host| unless `git rev-parse HEAD` === `git rev-parse origin/#{fetch(:branch, 'master')}` info "WARNING: local git is not synced with #{fetch(:branch, 'master')}" info "To solve this: Run git push origin #{fetch(:branch, 'master')} to sync" exit end end end # make sure that check_is_repo_updated runs after check_write_permissions task after :check_write_permissions, :check_is_repo_updated

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   desc "checks whether local git is in sync with remote" task :check_is_repo_updated do   on roles(:web) do |host|    unless `git rev-parse HEAD` === `git rev-parse origin/#{fetch(:branch, 'master')}`       info "WARNING: local git is not synced with #{fetch(:branch, 'master')}"       info "To solve this: Run git push origin #{fetch(:branch, 'master')} to sync"       exit     end   end end   # make sure that check_is_repo_updated runs after check_write_permissions task after :check_write_permissions, :check_is_repo_updated