What are the key principles of the Twelve-Factor App methodology?

Twelve-Factor App principles for SaaS: 1) Codebase (one repo per app), 2) Dependencies (explicitly declared), 3) Config (in environment), 4) Backing services (treat as attached resources), 5) Build/release/run (strict separation), 6) Processes (stateless, share-nothing), 7) Port binding (self-contained), 8) Concurrency (scale via processes), 9) Disposability (fast startup/shutdown), 10) Dev/prod parity, 11) Logs (as event streams), 12) Admin processes (one-off tasks). Foundation for cloud-native applications.