12 factor apps

12-factor apps

#1. One codebase, 1 application

• Code base to be backed by a version control system such as Git, Subversion etc., 
• 1 code base = 1 app. 
• Multiple apps sharing the same code is a violation of the 12-factor. 

#2. Dependencies

Manage dependencies in your application manifest. 

• Database, image processing libraries. 

Characteristics:

• Dependencies are managed in the app manifests such as maven, gradle etc., 

What should you do or don’t do: 

• Don’t use pre-installed softwares which will help in each environments. This will not automate the deployment. 
• Don’t assume that the related dependencies will be in the environment where you deploy, you are responsible for wiring the dependencies. 

#3. Externalize configuration

Application configuration referred here are values that are

• Credentials to access a database, or services such as S3. 
• Environment specific properties

Motivation: 

• Env properties stored in the code will be a violation since the code has to be redeployed whenever the properties changes. 
• Also its not a good idea to store env values in the code.

#4. Backing services

Are services that the app talks to 

Characteristics

• Services can be attached or detached whenever required. 

Objective:

• A different SMTP server should be able to be configured without the need for code change. 

#5. Build release run

Summary: 

Build: Application code gets converted into an artifact such as a war file. 

Release: the artifact now understands the environment - QA, Dev, Prod

Run: the app gets released in the specific environment. 

Characteristics

• Strict separation between the build, release and run stages of the application. 
• Every release must have a release id such as a timestamp or a incrementing number
• 1-click release - using CI/CD tool. 

What should you do: 

• Use a CI/CD tool, Jenkins, Concourse etc.,

Best Practices:

• Create smoke tests to ensure the app is running fine after deployment. 

#6. Stateless Processes

Characteristics:

• The process running in the environment should be stateless. 
• Should not share anything with other process. 
• No sticky sessions

What should do or don’t do. 

• Don’t store any data in a local file system. 
• Sessions: 
• Store your sessions if any in a distributed session storage db, such as Redis. 
• No sticky sessions. 
• Create stateless services. 

#7. Port binding

    The port binding for the application should be configurable and should not depend upon a particular infrastructure setup. 

#8. Concurrency

#9. Disposability

Your application should work fine even though one or more of app instances die. 

#10. Dev/Prod parity

Keep the developer environment as close as possible to the production environment. 

#11. Logs

Ensure it is easy to view / debug logs even though there may be multiple instances of the services exists. 

What should you do or don’t do:

• No System.out.printlns
• Write to log files on the web server using log4j like frameworks. 
• Stream logs to an external server where it can be viewed easily. Send the logs to a centralized logging facility. 

#12. Admin processes

Characteristics: 

• Execute any migration scripts on deployment of a startup if any. 

What should you do or don’t do: 

• Store migration scripts in the repository.