The 12-Factor App - 15 Years later. Does it Still Hold Up in 2026?

A thorough review of the Twelve-Factor App methodology, 15 years after its creation at Heroku. Each of the twelve factors is examined in the context of modern cloud-native development — containers, Kubernetes, serverless, GitOps, and AI workloads. Most factors hold up well and have become default practice; a few show their age (port binding for serverless, env vars as the only config mechanism, logs vs. full observability). The post also adds a 13th consideration not in the original: backward and forward compatibility during rolling deployments, covering database schemas, API contracts, cached data, and event schemas.