12-factor app methodologies and containerized environment


12-Factor app methodology has now become a de-facto standard for building Software-as-a-service (SaaS) applications………

But Wait!…..I don’t write SaaS apps, I’m a Software developer whose task is to write services. Just tell me how can I apply these principles in my daily development tasks?

Okay Okay! no problem…….let’s see the original principles first and see what each principle has to offer us for building modern cloud based web applications.

Trivia: The original 12-factor app methodology was drafted by engineers at Heroku and later on widely embraced by engineers around the globe.

Note: For this article we will consider Docker as default Container runtime and kubernetes as default container orchestration tool.

So, let’s dive in.


1. Codebase

Original: Each app should have it’s own single codebase and this codebase should be tracked in Version Control systems like Git, subversion, etc. Although each service can have any number of deployments or running instances.

If the codebase isn’t single then it is called a distributed system not an app and directly violates 12-Factor app Methodology.

Takeaway: It is easier to build the Docker image from a single codebase for deployment purposes. if your app spans over multiple codebases for a single service then each codebase can itself act as a 12-Factor app. Problem solved 😊


2. Dependencies

Original: Each app should explicitly declare its dependencies and should not rely on existence of system wide packages. These dependencies should be isolated from system installed packages leveraging some kind of isolation environment.

Lessons learnt:

  1. In containerised environment, each build starts with a fresh base image like alpine linux and we require some sort of declarative dependency management + Dockerfile to bundle things together and get our final image ready to deploy.

  2. Explicitly declaring dependencies with correct version/tag (not :latest) also ensures consistency across different systems and environments.


3. Config

Original: A config can be anything that varies between local, staging or production. environments. For ex, Database host IP, AWS credentials, Google API token, etc.

12-Factor method. suggests that config should be stored as environment variables.

Okay, I should practise this as Docker Containers and Orchestration tools like Kubernetes has in-built support to inject environment variables in containers at run-time.


4. Backing Services

A 12 factor app should treat Backing service like Databases, Memcache servers as attached resources and also a 12-factor app shouldn’t make any distinction between local and third-party resources. Furthermore, no change in codebase should be required when updating any of the backing services.

Okay! I got this, Due to ephemeral nature of containers, the backing services should be treated as attached resources and service should work seamlessly even when new container/instance of backing service rolls up and other one terminates.


5. Build, Release and Run

Original: Strictly separate Build, Release and Run stages.

Gotcha!, Dynamic nature of containers needs this kind of separation of concern. Image should be build and released with required config and run-time (or “run” stage) should not be dependent on Build and release stages as an image can be used to deploy infinite number of containers without building the image again.


6. Processes

Original: Every app instance should be run in a separate stateless process and no data should be shared between them using local filesystem and memory. If any data needs to be persist it should be stored in a separate shared database.

Oh! Finally, When you scale out your service by running multiple instances under a load balancer, you never expect that data stored in your local cache, memory or disk is available to your app even for very next request. Therefore, you need to write your code keeping statelessness in mind.


7. Port Binding

Original: Export services via port binding. The twelve-factor app is completely self-contained and does not rely on runtime injection of a webserver into the execution environment to create a web-facing service. The web app exports HTTP as a service by binding to a port, and listening to requests coming in on that port.

I know this, I know this Docker and orchestration tools like Kubernetes encourage this practice for exposing services and I already know this. Great! 🙂


8. Concurrency

Original: Scale out via process model. In a 12-Factor app, processes are first class citizen. The developer can architect their app to handle diverse workloads by assigning each type of work to a process type. For example, HTTP requests may be handled by a web process, and long-running background tasks handled by a worker process.

But, but If your app is containerised then you don’t need to worry about this. This is it.


9. Disposability

Original: The twelve-factor app’s processes are disposable, meaning they can be started or stopped at a moment’s notice. This facilitates fast elastic scaling, rapid deployment of code or config changes, and robustness of production deploys. Processes should strive to minimize startup time and focus on Graceful shutdown.

Again, I know this If your app is managed by orchestration tools like Kubernetes then you need not to worry about it, but still create your docker images as light as possible for faster boot-up. For best practices see this


10. Dev/prod parity

Original: Keep development, staging, and production as similar as possible.

My 2 Cents: If you practice declarative style of deployments using Docker containers and kubernetes. Dev prod parity can be achieved to a significant level. And also, tools like docker-compose can help you to achieve parity to a significant extent.


11. Logs

Original: Treat logs as event streams. Logs are the stream of aggregated, time-ordered events collected from the output streams of all running processes and backing services. each running process writes its event stream, unbuffered, to stdout

Oh! that’s why, All log aggregators recommend to write your logs to stdout instead of a file because you can’t track file names for each app or you have to set some standard for naming log files. Also Docker has docker logs and kubernetes has kubectl logs which display logs from containers’ stdout.


12. Admin processes

Original: Run admin/management tasks as one-off processes. One-off admin processes should be run in an identical environment as the regular long-running processes of the app. Admin code must ship with application code to avoid synchronization issues.

Again, Gotcha!, Ephemeral containers with same image tag should be used to run admin task. Another way is to use docker exec -it command to execute a command directly inside the containers.



12-Factor methodology may seem a set of guidelines for developing SaaS applications but believe me they are the standard way to build any modern web applications for scale. Nowadays, even many tools like Docker, Kubernetes, etc are directly or in-directly built over these principles.