500 errors after deploying / Gemfile missing database adapter

If you get a 500 error after deploying your application or the environment page of the Dashboard shows a warning about missing a database adapter, then you might be missing the mysql2 gem. This page describes how to find out if you are missing the mysql2 gem and how to install it.

To find out if you are missing the mysql2 gem

1. On your Dashboard, click Deployment history > View Log.

2. Search the deployments log for this error:

   Please install the mysql2 adapter: `gem install activerecord-mysql2-adapter` 
   (no such file to load -- active_record/connection_adapters/mysql2_adapter) 

If you find this message, install the mysql2 as described below (To install the mysql2 gem for a Rails 3.0.x application or To install the mysql2 gem for a Rails 3.1.x application).

To install the mysql2 gem for a Rails 3.0.x application

1. Add the latest version of the 0.2.x mysql2 gem to your Gemfile, for example:

   gem 'mysql2', '~> 0.2.13'

2. Run bundle install to update Gemfile.lock.

   bundle install 

3. If you get the error message “extconf.rb failed”, see To resolve the “extconf.rb failed” error below.

To install the mysql2 gem for a Rails 3.1.x application

1. Add the latest version of the 0.3.x mysql2 gem to your Gemfile, for example:

   gem 'mysql2', '~> 0.3.7' 

2. Run bundle install to update Gemfile.lock.

   bundle install 

3. If you get the error message “extconf.rb failed”, see To resolve the “extconf.rb failed” error below.

To resolve the "extconf.rb failed" error

• If you see the “extconf.rb failed” error after running bundle install above, do one of the following:

  • Install MySQL.
    If you want to do development on your local machine and test your applications on a MySQL database before deploying, then install MySQL. On Mac OS X, consider using Homebrew or MacPorts to install and configure MySQL.

  • Use Bundler groups. (This allows you to deploy your application without installing MySQL locally.)
    1. Add :group => :production to the gem ‘mysql2’ line in your Gemfile. For example,
       

        gem ‘mysql2’, ‘~> 0.2.13’, :group => :production

       or
       

        gem ‘mysql2’, ‘~> 0.3.7’, :group => :production

    2. Run bundle install without the production group:
       

        bundle install –without production

       
       When you deploy, mysql2 is installed if Framework Environment is set to production in your environment.

    About Bundler groups.  Bundler groups are for managing dependencies on different environments. By default, running bundle install installs dependencies for all of the groups. In Step 2 above, when you run bundle install locally, you skip the dependencies for the production group (which includes the mysql2 gem).

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