How can a company release new software many times a day?

A company can release new software many times a day because it has automated the road from a programmer's laptop to the customer. The practice is called continuous delivery: building software so that it can be released to production at any time. If the code is always in a releasable state, putting it live becomes a routine button press instead of a big event.

The road is called a deployment pipeline. Every time a change is saved to the shared code, a build server packages it, and then it goes through a series of tests before it is marked as ready to release. Fowler says the test of doing it right is that a business sponsor could ask for the current version to go live at a moment's notice, and nobody would panic. You can push any version to any environment on demand.

There is a second, bolder step. Continuous deployment sends every change that passes the pipeline straight into production without a human pressing the button, resulting in many deployments every day. Continuous delivery only means you could, and some businesses prefer a slower rhythm. Both are abbreviated CD, so it pays to ask which one people mean, and you cannot do the second without the first.

Why do it at all? Because small releases are safer. When you deploy smaller changes there is less to go wrong, and it is easier to fix a problem. Not everyone can do it: in fields such as medical devices, avionics and railways, regulations may require testing on the customer's own site.