CI/CD Patterns for Monorepos#

A monorepo puts multiple packages, services, and applications in a single repository. This simplifies cross-package changes and dependency management, but it breaks the assumption that most CI systems are built on: one repo means one build. Without careful pipeline design, every commit triggers a full rebuild of everything, and CI becomes the bottleneck.

The Core Problem#

In a monorepo, a commit that touches packages/auth-service/src/handler.ts should build and test auth-service and its dependents, but not billing-service or frontend. Getting this right is the central challenge of monorepo CI.

Integrating Infrastructure as Code with CI/CD#

Running Terraform locally works for one person. It breaks down when multiple people (or agents) modify infrastructure concurrently, when changes need review before applying, and when environments (dev/staging/prod) need synchronized promotion. CI/CD pipelines solve this by making the plan-review-apply cycle automated, auditable, and safe.

This article covers the patterns for integrating Terraform into CI/CD — from the basic plan-on-PR flow to multi-directory monorepos with dependency ordering and environment promotion.