Upgrading from OS X El Capitan to macOS High Sierra I'm in the process of planning an upgrade from OS X El Capitan to macOS High Sierra, and I'm using things like Homebrew, Composer, Elasticsearch, and — by extension — Java.

I'm using MAMP Pro with the files stored in: /Library/WebServer/Documents/.

I need to know if these things will remain intact after the upgrade, or whether I have to install them again afterwards?
All the software installed in macOS (along with the ones you mentioned) remain intact between OS upgrades.

However, it is advisable to keep an up-to-date backup before performing the upgrade.