Continuous Delivery

Continuous delivery (CD) is a software engineering approach in which teams produce software in short cycles, ensuring that the software can be reliably released at any time. It aims at building, testing, and releasing software faster and more frequently. The approach helps reduce the cost, time, and risk of delivering changes by allowing for more incremental updates to applications in production. A straightforward and repeatable deployment process is important for continuous delivery.

"Continuous Delivery is a software development discipline where you build software in such a way that the software can be released to production at any time" — Martin Fowler

Continuous integration (CI) is the practice, in software engineering, of merging all developer working copies to a shared mainline several times a day. Continuous Integration provides a framework for efficiently validating software in a predictable way. But to get the most out of it, you need to look at how it fits into the overall process of delivering software. In an agile project, you want to deliver working software at every iteration. Unfortunately, this is easier said than done; it often turns out that even if you implement CI and get the build process to produce a new installation package in a few minutes, it takes several days to get a new piece of software tested and released into production. To make this work better, the key is process. In order to deliver working software faster, you need a good cohesive set of tools and practices. So you need to add planning, environment management, deployment, and automated validation to get a great solution for your product, and this is just what Continuous Delivery is about.

Continuous Deployment is the practice of continuously pushing to production new versions of software under development. So Continuous Integration is all about quick feedback and validation of the commit phase, and Continuous Delivery is about establishing a mindset where you can deliver features at customer demand. Continuous Deployment is a third term that’s sometimes confused with both Continuous Integration and Continuous Delivery. Continuous Deployment can be viewed as the next level of Continuous Delivery. Where Continuous Delivery provides a process to create frequent releases but not necessarily deploy them, Continuous Deployment means that every change you make automatically gets deployed through the deployment pipeline. When you have established a Continuous Delivery solution, you are ready to move to Continuous Deployment if that’s something your business would benefit from.

Summary:
Continuous Integration is a software development practice in which you build and unit-test software every time a developer checks in new code.
Continuous Delivery (CD) is a software development practice in which continuous integration, automated testing, and automated deployment capabilities allow software to be developed and deployed rapidly, reliably and repeatedly with minimal manual overhead.
Continuous Deployment is a software development practice in which every code change goes through the entire pipeline and is put into production, automatically, resulting in many production deployments every day.