- Is Jenkins (or any other CI system) installed in the production server or I should have a separate server for Jenkins builds? If Jenkins is in another server, how can I integrate the builds as my running production code? Or this CI thing does have nothing to do with deploys?
Then I created a SSH key at /var/lib/jenkins/.ssh added to my Bitbucket >(Git) repository as Deployment key...
- Is this the correct approach?
That's correct. I have a bunch of servers configured this way. In the near future I want investigate if it would be possible to use the SSH Credentials Plugin to store my credentials there, so that I don't have to take care with the file system permissions for that key.
- Is this right? Should I run composer init on every build?
The main question maybe is: are my builds constructed from greenfield space? Should I checkout and run composer install and whatever scripts my project must take to be running every time (every build)?
It depends on your requirements. You can have several builds, or parametrize you build to support different behaviours. For instance, I have Laravel builds that depending on the environment parameter, they might do further testing with Selenium, or simply run phpunit.
I usually have two projects in Jenkins for each PHP application. One that checks out the code from git, clean any left-over of other builds in the workspace, and invokes Laravel's Envoy for building the project. What it basically does, is call composer install with some extra parameters, and call the migration and database seed routines to prepare the application for testing.
The other job is triggered when I promote (with Jenkins Promoted Builds Plugin) a build, and it copies (with the Copy Artifacts Plugin) the workspace created during build and already tested, and deploys it via scp to a folder in a QA server. It then updates some symbolic links, and finally it's ready to test.
With time and more requirements from developers and other teams, you'll get familiar with many other plug-ins, like the Email-ext Plug-in, to send custom notifications and include further information about the build.