Support auto-configuration of the DATABASE_URL environment variable

[tcdowney]

This is a feature suggestion, not a bug or problem, so I'm going to deviate from the normal template.

---

Background

Rails apps by convention use the contents of the DATABASE_URL environment variable to connect to the application's database.

Historically PaaSes have attempted to automatically configure this for developers based on what services they have bound:

• Heroku example
• Cloud Foundry example
  • As an aside, Cloud Controller is pretty unsophisticated in this area. It just grabs the first service binding it sees that has a uri credential.

Feature Suggestion

This is inspired by the spring-boot buildpack's support for CNB Bindings.

One of the existing Ruby sub-buildpacks or a more Rails-specific buildpack could exist that looks for CNB Bindings that match conventional types. Spring Cloud Bindings look for a variety of types like mysql, postgres, mongodb, etc. Or you could even do some introspection into the Gemfile (like the classic Heroku buildpack does) to have a better idea of what to look for.

Anyways, throwing this out there. Could be a quality-of-life improvement for Rails apps that want to use the Ruby CNB.

---

cc: @dsboulder who was digging into how DATABASE_URL was provided in CF with me and originally had this idea.

[sophiewigmore]

@tcdowney @dsboulder thanks for the issue. This seems like a reasonable ask, I'm going to transfer it to the Paketo Rails Assets buildpack repo!