capistrano/docs/documentation/overview/what-is-capistrano/index.markdown

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What is Capistrano?	default

Capistrano is a remote server automation tool.

It supports the scripting and execution of arbitrary tasks, and includes a set of sane-default deployment workflows.

Capistrano can be used to:

• Reliably deploy web application to any number of machines simultaneously, in sequence or as a rolling set
• To automate audits of any number of machines (checking login logs, enumerating uptimes, and/or applying security patches)
• To script arbitrary workflows over SSH
• To automate common tasks in software teams.
• To drive infrastructure provisioning tools such as chef-solo, Ansible or similar.

Capistrano is also very scriptable, and can be integrated with any other Ruby software to form part of a larger tool.

What does it look like?

What else is in the box?

There's lots of cool stuff in the Capistrano toy box:

• Interchangeable output formatters (progress, pretty, html, etc)
• Easy to add support for other source control management software.
• A rudimentary multi-console for running Capistrano interactively.
• Host and Role filters for partial deploys, or partial-cluster maintenance.
• Recipes for the Rails asset pipelines, and database migrations.
• Support for complex environments.
• A sane, expressive API:

desc "Show off the API"
task :ditty do

  on roles(:all) do |host|
    # Capture output from the remote host, and re-use it
    # we can reflect on the `host` object passed to the block
    # and use the `info` logger method to benefit from the
    # output formatter that is selected.
    uptime = capture('uptime')
    if host.roles.include?(:web)
      info "Your webserver #{host} has uptime: #{uptime}"
    end
  end

  on roles(:app) do
    # We can set environmental variables for the duration of a block
    # and move the process into a directoy, executing arbitrary tasks
    # such as letting Rails do some heavy lifting.
    with({:rails_env => :production}) do
      within('/var/www/my/rails/app') do
        execute :rails, :runner, 'MyModel.something'
      end
    end
  end

  on roles(:db) do
    # We can even switch users, provided we have support on the remote
    # server for switching to that user without being prompted for a
    # passphrase.
    as 'postgres' do
      widgets = capture "echo 'SELECT * FROM widgets;' | psql my_database"
      if widgets.to_i < 50
        warn "There are fewer than 50 widgets in the database on #{host}!"
      end
    end
  end

  on roles(:all) do
    # We can even use `test` the way the Unix gods intended
    if test("[ -d /some/directory ]")
      info "Phew, it's ok, the directory exists!"
    end
  end
end