Also worth reading is "Beyond the Twelve-Factor App" (O’Reilly). It goes into the 12 factors and expands them to 15 for cloud-native apps. I believe I got a free e-book via Pivotal's content library.
(1) One codebase, one application
(2) API first
(3) Dependency management
(4) Design, build, release, and run
(5) Configuration, credentials, and code
(6) Logs
(7) Disposability
(8) Backing services
(9) Environment parity
(10) Administrative processes
(11) Port binding
(12) Stateless processes
(13) Concurrency
(14) Telemetry
(15) Authentication and authorization
More info: https://content.pivotal.io/blog/beyond-the-twelve-factor-app