Act 1, scene 1: The premise and the line

Scene 1: The premise and the line

For decades, SaaS architecture has rested on one premise: writing the code is the expensive part. Four rules follow from it. Write the code once. Share every layer that can be shared. Express customer difference as configuration. Write custom code only where configuration runs out. Picture the product as a stack of layers with a line drawn through it. Below the line, everything is shared by every tenant. Above it sit only each customer's configuration values. The rules push that line as high as it will go, and they fix the product's flexibility at design time.