GitLab CE OmniBus enable MySQL (CentOS 7)

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From the documentation I see the gem for useing MySQL with the CE edition may not be installed. I do not want to use PostgreSQL due to having an existing server. Is there a way to modify this to enable me to use MySQL? I already seem to have it working with external redis and nginx but not MySQL.

The issue is I am getting 502 when connecting to the nginx instance and it has the following error:

502
Whoops, GitLab is taking too much time to respond.

Try refreshing the page, or going back and attempting the action again.

Please contact your GitLab administrator if this problem persists.

The unicorn error log shows the following:

[root@gitlab ~]# tail -n50 /var/log/gitlab/unicorn/unicorn_stderr.log
        from /opt/gitlab/embedded/service/gitlab-rails/config.ru:1:in `<main>'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/unicorn-4.8.3/lib/unicorn.rb:48:in `eval'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/unicorn-4.8.3/lib/unicorn.rb:48:in `block in builder'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/unicorn-4.8.3/lib/unicorn/http_server.rb:764:in `call'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/unicorn-4.8.3/lib/unicorn/http_server.rb:764:in `build_app!'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/unicorn-4.8.3/lib/unicorn/http_server.rb:137:in `start'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/unicorn-4.8.3/bin/unicorn:126:in `<top (required)>'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/bin/unicorn:23:in `load'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/bin/unicorn:23:in `<main>'
I, [2016-02-28T10:13:23.315917 #9388]  INFO -- : Refreshing Gem list
/opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.5.1/lib/active_record/connection_adapters/connection_specification.rb:177:in `rescue in spec': Specified 'mysql2' for database adapter, but the gem is not loaded. Add `gem 'mysql2'` to your Gemfile (and ensure its version is at the minimum required by ActiveRecord). (Gem::LoadError)
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.5.1/lib/active_record/connection_adapters/connection_specification.rb:174:in `spec'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.5.1/lib/active_record/connection_handling.rb:50:in `establish_connection'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.5.1/lib/active_record/railtie.rb:120:in `block (2 levels) in <class:Railtie>'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activesupport-4.2.5.1/lib/active_support/lazy_load_hooks.rb:38:in `instance_eval'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activesupport-4.2.5.1/lib/active_support/lazy_load_hooks.rb:38:in `execute_hook'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activesupport-4.2.5.1/lib/active_support/lazy_load_hooks.rb:28:in `block in on_load'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activesupport-4.2.5.1/lib/active_support/lazy_load_hooks.rb:27:in `each'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activesupport-4.2.5.1/lib/active_support/lazy_load_hooks.rb:27:in `on_load'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/activerecord-4.2.5.1/lib/active_record/railtie.rb:116:in `block in <class:Railtie>'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/railties-4.2.5.1/lib/rails/initializable.rb:30:in `instance_exec'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/railties-4.2.5.1/lib/rails/initializable.rb:30:in `run'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/railties-4.2.5.1/lib/rails/initializable.rb:55:in `block in run_initializers'
        from /opt/gitlab/embedded/lib/ruby/2.1.0/tsort.rb:226:in `block in tsort_each'
        from /opt/gitlab/embedded/lib/ruby/2.1.0/tsort.rb:348:in `block (2 levels) in each_strongly_connected_component'
        from /opt/gitlab/embedded/lib/ruby/2.1.0/tsort.rb:427:in `each_strongly_connected_component_from'
        from /opt/gitlab/embedded/lib/ruby/2.1.0/tsort.rb:347:in `block in each_strongly_connected_component'
        from /opt/gitlab/embedded/lib/ruby/2.1.0/tsort.rb:345:in `each'
        from /opt/gitlab/embedded/lib/ruby/2.1.0/tsort.rb:345:in `call'
        from /opt/gitlab/embedded/lib/ruby/2.1.0/tsort.rb:345:in `each_strongly_connected_component'
        from /opt/gitlab/embedded/lib/ruby/2.1.0/tsort.rb:224:in `tsort_each'
        from /opt/gitlab/embedded/lib/ruby/2.1.0/tsort.rb:205:in `tsort_each'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/railties-4.2.5.1/lib/rails/initializable.rb:54:in `run_initializers'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/railties-4.2.5.1/lib/rails/application.rb:352:in `initialize!'
        from /opt/gitlab/embedded/service/gitlab-rails/config/environment.rb:5:in `<top (required)>'
        from /opt/gitlab/embedded/service/gitlab-rails/config.ru:16:in `require'
        from /opt/gitlab/embedded/service/gitlab-rails/config.ru:16:in `block in <main>'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/rack-1.6.4/lib/rack/builder.rb:55:in `instance_eval'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/rack-1.6.4/lib/rack/builder.rb:55:in `initialize'
        from /opt/gitlab/embedded/service/gitlab-rails/config.ru:1:in `new'
        from /opt/gitlab/embedded/service/gitlab-rails/config.ru:1:in `<main>'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/unicorn-4.8.3/lib/unicorn.rb:48:in `eval'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/unicorn-4.8.3/lib/unicorn.rb:48:in `block in builder'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/unicorn-4.8.3/lib/unicorn/http_server.rb:764:in `call'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/unicorn-4.8.3/lib/unicorn/http_server.rb:764:in `build_app!'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/unicorn-4.8.3/lib/unicorn/http_server.rb:137:in `start'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/gems/unicorn-4.8.3/bin/unicorn:126:in `<top (required)>'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/bin/unicorn:23:in `load'
        from /opt/gitlab/embedded/service/gem/ruby/2.1.0/bin/unicorn:23:in `<main>'
I, [2016-02-28T10:13:34.636709 #9413]  INFO -- : Refreshing Gem list

I even installed the mysql2 as shown below with the same result and it is in the Gemfile.

[root@gitlab ~]# /opt/gitlab/embedded/bin/gem list | grep mysql
mysql2 (0.3.16)

[root@gitlab ~]# grep mysql /opt/gitlab/embedded/service/gitlab-rails/Gemfile
gem "mysql2", '~> 0.3.16', group: :mysql
2

@b952000 Unfortunately, only PostgreSQL is supported on GitLab CE. To use MySQL please upgrade to EE.

Visit our feature’s page to read more on more CE vs EE differences: https://about.gitlab.com/features/