Using CI in "blue-green" deployment

Hello!

I'm assuming you're going to be automating your blue-green deployment. I've done this on AWS using both Opsworks and ElasticBeanstalk and had it working.

For database changes, you have to use migrations. Manually updating the database is a terrible idea when trying to automate deployments. If you're not a fan of CI's migrations, there are several other tools that you can use too. I quite enjoy Phinx.

When it comes to config files, it's a good idea to put them in an environment variable so you'll access with $_SERVER. Every automation tool i've dealt with has given an option to inject those env variables on deploy or launch

Codeigniter is simply one of the tools you need to learn to be a successful developer. Always add more tools to your coding arsenal!