资深程序员之路(4)--如何做持续集成和部署
现在开始换英文的。
Continuous Integration (CI)
In traditional software development the process of integration generally took place at the end of a project after each person had completed their work. Integration generally took weeks or months and could be very painful. Continuous integration is a practice that puts the integration phase earlier in the development cycle so that building, testing and integrating code happens on a more regular basis.
CI means that one developer (hi Steve!) who writes code on his laptop at home, and another dev (hey Annie!) who codes on her desktop in the office can both write software for the same product separately, integrate their changes together in a place called the source repository. They can then build the combined software from the bits they each wrote and test that it works the way they expect.
Developers generally use a tool called the CI Server to do the building and the integration for them. CI requires that Steve and Annie have self-testing code. This is code that tests itself to ensure that it is working as expected, and these tests are often called unit tests. When all the unit tests pass after the code is integrated Steve and Annie will get a green build. This indicates that they have verified that their changes are successfully integrated together, and the code is working as expected by the tests. However, while the integrated code is successfully working together, it not yet ready for production because it has not been tested and verified as working in production-like environments. You can read more about what happens after CI in the Continuous Delivery section below.
To be considered to be practicing CI, Steve and Annie must check-in to the main source repository, integrate and test their code frequently and often. Usually many times an hour, but at a minimum once a day.
The benefit of CI is that integration becomes a non-event. Software is written and integrated all the time. Before CI, integration happened at the end of the creation process, all at once, and took an unknown amount of time; now with CI, it happens everyday, takes minutes and is just “the way we work”.
It’s most likely the your team is doing CI (or at least they believe they are). You can confirm by asking them whether they integrated code once a day.
Continuous Delivery (CD)
Let’s go back to our two developers, Steve and Annie. Continuous Delivery means that each time Steve or Annie makes changes to the code, integrates and builds the code, that they also automatically test this code on environments that are very similar to production. We call this progression of deploying to – and testing on – different environments a deployment pipeline. Often the deployment pipeline has a development environment, a test environment, and a staging environment, but these stages vary by the team, product and organisation. For example, our Mingle team has a stage called “Cupcake” which is a staging environment, and Etsy’s staging environment is called “Princess”.
In each different environment, the code that Annie or Steve wrote is tested differently. This gives more and more confidence to them, and to you, that the code will work on the production environment when the code is deployed there. Crucially, the code is only promoted to (tested on) the next environment in the deployment pipeline if it passes the tests of the previous environment. This way Annie and Steve get new feedback from the tests in each environment and, if there is a failure, they can understand more easily where the issue might be and get it fixed before the code gets to the production environment.
Continuous Deployment
This is a practice where every change that Steve or Annie makes, and which passes all the test stages, automatically goes to production. Tim Fitz has a great explanation of it as it was first coined. Some companies do this and others do not. To achieve continuous deployment you first need to get to continuous delivery, so it’s not a priority to decide which is better for you until you’ve starting practicing CD. Either way, I’m of the opinion that continuous delivery is about empowering the business as a whole, and so at the very least you should be involved in deciding if you should use continuous deployment or not. After all, if you’re reading this then you’re probably on the “business side”.