This feature has been around for a while, but there still might be some of you unaware that you can attach services to Docker containers and use them in your builds. The feature is free with no limits imposed and includes the following services:
List of actions that support services
How to attach services to your build
Click the build action that you want to use and switch to the Services tab
Click the Attach button to expand the list of services available
Once you select the service it'll be attached to your build and connection details presented
Make sure to Save your changes when you're done!
Not that data stored in the service is not persistent between executions: everything is recreated from scratch on each execution.