Build Once, Deploy Many — A Staging-to-Production Pipeline with GCP Cloud Deploy

Introduction — "Build Once, Deploy Everywhere" When building CI/CD pipelines, do you find yourself with a setup like this? Build for staging → Deploy to staging Build for production → Deploy to production Rebuilding for each environment comes with several problems: No reproducibility — The binary running in staging isn't guaranteed to be identical to the one in production Doubled build time — Building the same source code twice is wasteful Harder incident debugging — When something breaks in production, it's difficult to determine whether it's a code issue or a build discrepancy Build Once, Deploy Many is a simple answer to this problem. You build a single immutable container image and deploy that exact same image to both staging and production. In this article, we'll walk through a real-world implementation using the CI/CD pipeline of Lasimban (羅針盤), a Scrum task management SaaS, using GCP's Cloud Build + Cloud Deploy + Kustomize. Architecture Overview — The Pipeline at a Glance Let's