When a Scalingo for MySQL® addon is provisioned, the platform also adds two environment variables to your app:

• SCALINGO_MYSQL_URL: a string containing all information needed to establish a connection between your application and your database. This string is called a connection URI.
• DATABASE_URL: an alias for SCALINGO_MYSQL_URL.

Understanding the Connection URI

The connection URI is made of several components separated one from each other by a delimiter. For example, the @ character is used to mark the end of the userinfo (credentials) component of the URI.

In the case of MySQL®, the connection URI provided by Scalingo is always formed as follows:

mysql://[user]:[password]@[url]:[port]/[dbname]?useSSL=true&verifyServerCertificate=false

For more information about the connection URI syntax, please see RFC 3986 which defines the URI Generic Syntax.

Using the Connection URI

We strongly advise to use one of the two environment variables available to connect your application to your database. Please don’t use the value, but the environment variable itself.

While the value of the provided connection URI should not change over time, we don’t guarantee it. For example, the URI could change for maintenance reasons. In such a case, using the environment variable guarantees that your application can restart successfully without human intervention. Otherwise, you would have to update your code with the new value and trigger a new deployment, which would most probably contribute to a bigger downtime.

In most cases, you can pass the environment variable directly to the client library you are using. But sometimes, the library requires a specific URI format, invididual keypairs or another format. In such cases, your code needs to parse the connection URI to retrieve the different values and build what’s required by the library. Our advice to use the environment variable still remains applicable.

Getting the Connection URI

Using the Dashboard

1. From your web browser, open your dashboard
2. Click on the application for which you want to get the connection URI
3. Click on the Environment tab
4. Locate the SCALINGO_MYSQL_URL line and place your mouse over it to unblur the value

Using the Command Line

1. Make sure you have correctly setup the Scalingo command line tool
2. From the command line, get the environment variable value:

   scalingo --app my-app env-get SCALINGO_MYSQL_URL
   

   The output should look like:

   mysql://my_app_wxyz:Q7X7CU2vGjFiLZrA43OG@7e10d74b-c766-40b3-8dad-ce9cfa461311.my-app-wxyz.mysql.a.osc-fr1.scalingo-dbs.com:31000/my_app_wxyz?useSSL=true&verifyServerCertificate=false
   

Enforcing TLS Connection

All MySQL® addons support TLS to encrypt all the network traffic between the client and the server.

By default, all new MySQL® databases have TLS available, which means that you don’t have to do anything to connect via TLS with a tool or library that uses TLS by default.

If you want to enforce TLS connections to your database so that TLS is not only available, but mandatory:

1. From your web browser, open your database dashboard
2. Select the Overview tab
3. Locate the TLS/Internet Access block
4. Toggle the corresponding option:

Once this option is activated, the database denies any non-TLS connection. Consequently, your application must be configured to use TLS when connecting to the database.

Please note that while we strongly advise to use TLS, it remains an option, meaning that you can still access your database without it if needed.

Connecting Multiple Applications to the Same MySQL® Addon

It’s possible to make multiple applications use the same MySQL® addon. To do so, add an environment variable in every application that needs to connect to the database, like so:

1. Copy the connection URI of your addon
2. Create a new environment variable for the application that needs to connect to the addon
3. Set the value of this new environment variable to connection URI you just copied
4. Restart the application to make the new environment variable available
5. Remember to update this new environment variable whenever the original connection URI changes

Using Ruby on Rails

When using Ruby on Rails, the buildpack reads the DATABASE_URL environment variable (which is an alias for SCALINGO_MYSQL_URL), parses it and creates the database.yml configuration file accordingly and automatically.

If you’re using the mysql2 gem, you will need to copy the value of SCALINGO_MYSQL_URL into DATABASE_URL and change the scheme part from mysql:// to mysql2://.