With that said, we also do a read only branch called stable that we only push to once unstable gets the OK in Jenkins. I would not say that it is dead, but just an extra safe guard. I do appreciate that book recommendation on http://www.amazon.com/gp/product/0321601912/ I have not heard of that before.
Did you just put your Amazon associates referral code in a link on HN? lol
Continuous Integration is fundamentally about creating a tight feedback loop between your developers and your code. When you program in your IDE, the instant you write uncompilable code, you get red squigglies, so you're getting an instant feedback loop on something you just wrote.
CI is the same thing, but at a higher level. The instant you commit your code, some automated process should take over and start analyzing / compiling / testing your code and look for things to give you feedback on. If your code doesn't even compile -- one of the first milestones of CI, you should know that immediately.
Since you just committed it, making the fix is easy. This is compared to a developer who downloads your code the next day, can't compile, comes and bugs you about it, etc...
As far as some real world use cases, we just setup Jenkins for a new Java project we're writing. It does an automated build test that compiles and executes all unit tests automatically on any commit to GitHub on any branch. It's a little slower than I like -- our still growing app takes a full 3 minutes to compile and give feedback.
But, it's been great. For example, the GitHub client on Mac OS X doesn't recognize when I change uppercase letters to lowercase and vice versa, so while my local compiles worked fine, my repo actually had a failing build. Once I committed, I got an automated email within 5 minutes telling me the build failed, and I fixed it. Without CI, I may not have found about that issue for weeks, making the change more difficult.
For production deployment, we're still in alpha, but we've got a 1-button push to deploy. Again, slower than it should be -- in this case 5 minutes -- but the automation is awesome and makes doing any deployment -- whether hot fixes or new releases that much more pleasant.
Regarding the performance, I see it as a win just to get anything automated, however slow it may be. Because once you're there, you can always look for ways to optimize it. For example, our current build process, re-downloads dependencies every single time. This could clearly be cached. When it's a priority for us, we'll do it.
[1] http://www.amazon.com/gp/product/0321601912
[2] http://timothyfitz.wordpress.com/2009/02/10/continuous-deplo...
Everyone should read Continuous Delivery to start (https://www.amazon.com/gp/product/0321601912/ref=as_li_tl?ie...). It's 10 years old but it's still the canonical reference for how most people should be deploying in the modern age.
A book on containers would be the next thing I'd learn very thoroughly. Whether you run them in Docker on a single host, or run them in a cloud orchestration system, doesn't matter really. Just having an app in a container provides the abstractions you want to enable rapid, reliable deployment on multiple platforms. Most deployments should be dead simple: pulling and starting a new container, pointing traffic at the new container, stopping the old one. Rollback is the same in reverse order of container. There should be a billion different services to manage this for you, but you can also do it yourself on a single Linux box easily.
Then a book on database migrations, which isn't really complicated once you get the jist of it. This teaches the idea that if you're using a database, you have to think hard about how you're using it in context of your code deployments, and gives you a model for how to handle both reliably.
Next, the tools Terraform and Packer are very useful for handling the "infrastructure" side of deployment. If you manage an actual VM that runs your apps, build the image with Packer and deploy it with Terraform. It's much better to use some managed provider that just runs your containers so you don't need to deal with this. But if you do need to manage a host OS, this will make it seamless and reliable to do the inevitable maintenance in a way that you can test first, and recover easily from failure.
Ensuring your app works along the methods of the 12 Factor App (it's just a website, no book) will make sure it fits into all the tools and methods. If you just look for the deployment piece of every part of 12FA, you'll build a very robust deployment system.
Finally, learn Bash and how to set up a web server like Nginx (and how to use it as a reverse proxy) and you will have basically all the skills you need to do modern best practice deployments.