workflow

Create a pull request from your branch.
Deploy the branch using Capistrano.
Verify that the changes work.
Merge in the pull request.
Deploy the master branch using Capistrano.

Add to deploy.rb

set :branch, ENV['BRANCH'] || "master"

Add to deploy.rake

desc "updates BRANCH file to 'block' deploy when some other or other's branch is deployed"
task :put_branch do
  branch_to_deploy = "#{fetch(:branch)}"
  on roles(:app) do
    execute "echo \"#{branch_to_deploy}:#{ENV['USER']}\" > #{release_path}/BRANCH"
  end
end

desc "read BRANCH file to let branch deploy when there is no other or other's branch deployed"
task :check_branch do
  on roles(:app) do
    current_branch_info = capture("cat #{current_path}/BRANCH")
    current_branch_info ||= "master"
    current_branch = current_branch_info.split(':')[0]
    deployer = current_branch_info.split(':')[1]
    branch_to_deploy = "#{fetch(:branch)}"

    if branch_to_deploy != 'master' && current_branch != 'master' && current_branch != branch_to_deploy
      puts "*************************************************************"
      puts " Sorry, #{deployer} is already deploying the feature #{current_branch}"
      puts "*************************************************************"
      exit
    end
  end
end

if ENV['BRANCH']
  before "deploy", "deploy:check_branch"
end
after :published, "deploy:put_branch"

Deploy branches with Capistrano

workflow