Beyond the Twelve-Factor App

Chapter 7. Disposability

Disposability is the ninth of the original 12 factors.

On a cloud instance, an application’s life is as ephemeral as the infrastructure that supports it. A cloud-native application’s processes are disposable, which means they can be started or stopped rapidly. An application cannot scale, deploy, release, or recover rapidly if it cannot start rapidly and shut down gracefully. We need to build applications that not only are aware of this, but also embrace it to take full advantage of the platform.

Those used to developing in the enterprise world with creatures like application containers or large web servers may be used to extremely long startup times measured in minutes. Long startup times aren’t limited to just legacy or enterprise applications. Software written in interpreted languages or just written poorly can take too long to start.

If you are bringing up an application, and it takes minutes to get into a steady state, in today’s world of high traffic, that could mean hundreds or thousands of requests get denied while the application is starting. More importantly, depending on the platform on which your application is deployed, such a slow start-up time might actually trigger alerts or warnings as the application fails its health check. Extremely slow start-up times can even prevent your app from starting at all in the cloud.

If your application is under increasing load, and you need to rapidly bring up more instances to handle that load, any delay ...