Understanding Continuous Integration, Delivery, and Deployment

Overview

Internet software development and release follow a standard process, with Continuous Integration (CI) as the core component.

Continuous Integration

CI means frequently (multiple times a day) merging code into the main branch.

Benefits:

Rapid error detection: each small update is integrated and tested immediately, making bugs easier to locate.

Prevents large branch drift that makes later integration difficult.

Martin Fowler: “Continuous integration does not eliminate bugs, but makes them very easy to find and fix.”

After developers submit new code, a build and unit tests run immediately; test results determine whether the new code integrates correctly with existing code.

Continuous Delivery

Continuous Delivery (CD) means frequently delivering new software versions to a quality team or users for review. If the review passes, the code proceeds to production.

CD builds on CI by deploying the integrated code to a production‑like environment (e.g., a Staging environment with a database) for further testing before manual deployment to production.

Continuous Deployment

Continuous Deployment is the next step after Continuous Delivery: once code passes review, it is automatically deployed to the production environment.

The goal is that the code is always deployable, requiring automated testing, building, and deployment pipelines.