Add support for setting DATABASE_URL from vcap services

[tomkennedy513]

• This is replicating behavior that exists in buildpack app lifecycle

[tomkennedy513]

Just bumping this @cloudfoundry/wg-app-runtime-platform-cnbapplifecycle-approvers since its been open over a month

[modulo11]

I cannot find any usage of DATABASE_URL in the Paketo Buildpacks. Not sure why we should add it.

[tomkennedy513]

I cannot find any usage of DATABASE_URL in the Paketo Buildpacks. Not sure why we should add it.

It's for apps to use primarily, but buildpacks can use it to make decisions on things like providing database drivers. This is supported for all other lifecycles on cf

[pbusko]

@tomkennedy513 is there an option to have a reusable version of this function? As you mentioned, this code must be the same across all existing lifecycles. It seems that the dockerapplifecycle imports some functions from the buildpackapplifecycle. Should this be extracted to a new repository which contains shared logic?

[tomkennedy513]

I copied it over (though I did tweak it a bit) because I remember when I did the credhub interpolation there was a strong desire to not have any cross lifecycle dependencies. A third repo make senses but obviously requires a lot more coordination to get this change in

[pbusko]

Since we already have quite a lot of common things between the lifecycles, I believe it's time to introduce the library repository. What is your opinion on that?

[tomkennedy513]

I think adding a library makes sense, but I think that should be separate from getting this fix in to unblock us.