Before you invest in blue-green deployment

It comes up on almost every project, usually later than it should. Before you spend anything on blue-green deployment, it is worth confirming a few things are already true.

The bill is a design document: it tells you exactly what your architecture actually does. If it only works because one person remembers to do something, it does not work yet.

Prerequisites

• You can describe the outcome you want in one sentence
• Someone owns it after the work is done
• Running two environments makes rollback instant
• You have a way to tell whether it worked

The mistakes we see most

Database changes are what make it complicated. This is the sort of thing that compounds, quietly, in both directions. The version that survives contact with a real deadline is the simple one.

Practise the rollback before you need it. The cost of getting this wrong is rarely visible on the day it happens. Anything you cannot measure here, you are deciding by taste, which is fine as long as everyone knows it.

The short version

Cloud work rewards teams who automate early and punishes teams who click through consoles. Three things worth confirming about blue-green deployment before you move on:

• Someone can say what the current setup is without going to look
• Practise the rollback before you need it — and you know whether that is true here
• There is a way to tell whether the last change to this helped

The point is not perfection, it is knowing which of these you have consciously chosen to skip.