👋 Hey,
A few years ago, the basic practices and theories behind building a quality application weren’t easy to come by. You learned them the hard way: you’d hardcode a database connection straight into the code, ship it, and only discover during the outage that promoting it to another environment meant rebuilding the whole thing. Then the 12-Factor App put those lessons into words.
It’s old, but as people say… “old but gold.” And honestly, I think every SRE should know it. These are items so simple, yet so rarely used and reviewed. And an SRE, precisely because they work with reliability, is the right person to materialize the twelve factors for almost any application with little effort — or, these days, with little more than a good prompt.
What Is the Twelve-Factor App?
The Twelve-Factor App was created by Heroku as a set of best practices for building modern applications: portable, scalable, and ready to run well in cloud environments.
It isn’t just a technical checklist. It’s a development and operations philosophy that helps teams build applications that are easier to configure, scale, observe, replace, and operate. The twelve factors are:
- Codebase
- Dependencies
- Config
- Backing Services
- Build, Release, Run
- Processes
- Port Binding
- Concurrency
- Disposability
- Dev/Prod Parity
- Logs
- Admin Processes
You don’t need all twelve top of mind. But a handful of them map almost one-to-one onto the things an SRE cares about every day.
SRE and the Config Factor
Every SRE should help application teams understand that software needs to run in different environments without changing the code.
That’s exactly the idea behind the Config factor: separate configuration from code. The application should receive its configuration before startup — usually through environment variables, secrets, or config maps. With that in place, the same code runs in dev, staging, and production by changing only the external configuration.
SRE, Dev/Prod Parity and Build, Release, Run
This connects directly to Dev/Prod Parity and Build, Release, Run.
When config and backing services are well defined, it becomes much easier to keep environments alike. The difference between dev, stage, and production lives in the variables and connected resources, not in the code. That simplifies building, releasing, and running the application in any environment — in minutes, and with far less risk.
SRE, Logs and Metrics
Another essential one for SRE is the Logs factor.
Every application needs to produce logs that are clear, accessible, and ideally structured. Logs are fundamental for investigating problems, understanding application behavior, generating metrics, creating alerts, and improving observability. Without good logs and good metrics, the SRE is practically blind in production.
SRE and Disposability
And of course, there’s Disposability.
Modern applications need to start fast, shut down gracefully, and be easily replaced. To pull that off, they should avoid storing state locally and stay as stateless as possible. That makes restart, deploy, autoscaling, rollback, and failure recovery far simpler. For SRE, this is essential to keep applications simple, resilient, and easy to operate.
Conclusion
In the end, the Twelve-Factor App is one more quality mechanism that connects directly to the essence of SRE.
An SRE needs to know these factors to bring technical arguments into discussions with teams and influence good architecture and operations decisions. Many of these concepts seem simple, yet they’re still heavily neglected day to day — and when that happens, it’s the operation that pays for it later.
So use the Twelve-Factor App, and other good practices, as technical ammunition to defend quality, reliability, observability, and resilience. If you work as an SRE and don’t yet know the Twelve-Factor App well, it’s well worth studying, understanding, and getting familiar with these factors.
Which factor do you see broken most often, and which one has burned you worst? Reply and tell me. 🔧
That’s what I had for today.
See you next time 👋
Cheers,
Douglas Mugnos
MUGNOS-IT 🚀
