Introduction

A team deploys a payment service on Friday. On Monday the database moves to a new machine. The address of that database sits inside the service code. Changing it means editing the code, building the service again, and deploying it again. The value that changed is nine characters long. The work it caused takes half a day.

This chapter is about that problem. The pattern that solves it is called Configuration Externalization. It keeps settings outside the code, so changing a setting does not mean shipping the code again.