Instructions on converting GitLab 4.2 from unicorn to puma.

GL4.2-UnicornToPuma

1) Delete the line containing 'unicorn' from Gemfile
2) Add the following line under the "Servers" section
    gem "puma", "~> 1.6.3"
3) From /home/gitlab/gitlab run
    sudo bundle install --no-deployment
4) From /home/gitlab/gitlab run the install command that fits the database you are using, I use MySQL
    sudo -u gitlab -H bundle install --deployment --without development test postgres
5) Create a new file config/puma.rb. Put the following inside it
    #!/usr/bin/env puma

    #Available options for 1.6.3 can be found here: http://rubydoc.info/gems/puma/1.6.3/Puma/Configuration/DSL

    environment = :production
    pidfile '/home/gitlab/gitlab/tmp/pids/puma.pid'
    state_path '/home/gitlab/gitlab/tmp/pids/puma.state'
    bind 'unix:///home/gitlab/gitlab/tmp/sockets/puma.sock'
6) In /etc/nginx/sites-available/gitlab, change the gitlab upstream to
    server unix:///home/gitlab/gitlab/tmp/sockets/puma.sock;
7) From /home/gitlab/gitlab run 
    sudo -u gitlab -H puma -e production -C /home/gitlab/gitlab/config/puma.rb

At this point, you should be able to hit your old GitLab URL in a browser.

Replacing the unicorn management in init.d/gitlab still needs to be done

For GitLab 6.0.0 I had to change step 7 to:

sudo -u git -H bundle exec puma -e production -C /home/git/gitlab/config/puma.rb