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Capistrano Cheat Sheet

A quick reference guide for Capistrano, a remote server automation and deployment tool written in Ruby. This cheat sheet covers essential commands, configuration options, and deployment strategies.

Core Concepts & Setup

Installation

Install Capistrano gem:

gem install capistrano

Add to your project’s Gemfile:

group :development do
  gem 'capistrano', require: false
end

Then run bundle install

Initialize Capistrano in your project:

cap install

This creates Capfile, config/deploy.rb, and config/deploy/*.rb.

Key Configuration Files

Capfile

Loads Capistrano’s tasks and recipes. Require other capistrano plugins here.

config/deploy.rb

Main configuration file for settings applicable across all environments (staging, production, etc.).

config/deploy/[environment].rb

Environment-specific settings (e.g., server addresses, user roles) for staging, production, etc.

Basic Configuration Settings

set :application, 'my_app' - Sets the application name.

set :repo_url, '[email protected]:user/my_app.git' - Sets the repository URL.

set :deploy_to, '/var/www/my_app' - Sets the deployment directory on the server.

set :branch, :master - Sets the branch to deploy.

set :linked_files, %w{config/database.yml config/secrets.yml} - Files to be linked from shared directory to current release.

set :linked_dirs, %w{log tmp/pids tmp/cache tmp/sockets vendor/bundle public/system} - Directories to be linked.

Common Capistrano Commands

Deployment Commands

cap [environment] deploy - Deploys the application to the specified environment (e.g., cap production deploy).

cap [environment] deploy:check - Checks if all dependencies are met before deployment.

cap [environment] deploy:cleanup - Removes old releases from the server.

cap [environment] deploy:rollback - Rolls back to the previous release.

cap [environment] deploy:failed - Check if the deployment failed.

Server Management

cap [environment] server:status - Checks the status of servers.

cap [environment] puma:start - Start the Puma server.

cap [environment] puma:stop - Stop the Puma server.

cap [environment] puma:restart - Restart the Puma server.

Utility Commands

cap -T - Lists all available tasks.

cap [task] -D - Displays the task’s description.

cap [environment] invoke:command command='your_command' - Executes a command on the server.

Advanced Configuration

Hooks

Hooks allow you to run custom tasks at specific points during the deployment process. Common hooks include:

:before - Runs before a task.
:after - Runs after a task.

Example: Run a task before deploy:migrate:

before 'deploy:migrate', 'my_custom_task'

Custom Tasks

Define custom tasks in lib/capistrano/tasks/my_task.rake:

namespace :my_namespace do
  desc 'My custom task'
  task :my_custom_task do
    on roles(:app) do
      within release_path do
        execute :rails, 'runner', "MyModel.do_something"
      end
    end
  end
end

Roles

role :web, %w{[email protected] [email protected]}

Defines web servers.

role :app, %w{[email protected]}

Defines application servers.

role :db, %w{[email protected]}, primary: true

Defines the database server (marked as primary).

SSH Configuration

set :ssh_options, { forward_agent: true, user: 'deploy', keys: %w(~/.ssh/id_rsa.pub) } - Configures SSH options.

Tips and Troubleshooting

Common Issues

Permission Denied: Ensure the deploy user has necessary permissions on the server (e.g., ownership of the deployment directory).

SSH Key Issues: Verify the SSH key is added to the server’s authorized_keys file and the forward_agent option is enabled if using agent forwarding.

Linked Files/Directories: Double-check that linked files and directories exist in the shared directory and have the correct permissions.

Branch not found: Verify the specified branch exists in the repository.

Debugging

Use cap [environment] deploy -V for verbose output to see detailed logs during deployment.

Check server logs in /var/www/my_app/current/log/ for application-specific errors.

Best Practices

Use a dedicated deploy user on the server with limited privileges.

Keep your deploy.rb and environment-specific files clean and organized.

Test your deployment process in a staging environment before deploying to production.

Automate database backups as part of your deployment process.
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