Where did everything go in Puppet 4.x?

This is a summary of [1] at docs.puppet.com.

• New All-in-One puppet-agent package - On managed *nix systems, you’ll now install puppet-agent instead of puppet. (This package also provides puppet apply, suitable for standalone Puppet systems.) It includes tools (private versions) like Facter, Hiera, and Ruby; also MCollective.

• *nix executables are in /opt/puppetlabs/bin/ - On *nix platforms, the main executables moved to /opt/puppetlabs/bin. This means Puppet and related tools aren’t included in your PATH by default. You have to add it to your PATH or use full path when running puppet commands. 

1. Private bin directories - The executables in /opt/puppetlabs/bin are just the “public” applications that make up Puppet. Private supporting commands like ruby and gem are in /opt/puppetlabs/puppet/bin

• *nix confdir is Now /etc/puppetlabs/puppet - Puppet’s system confdir (used by root and the puppet user) is now /etc/puppetlabs/puppet, instead of /etc/puppet. Open source Puppet now uses the same confdir as Puppet Enterprise.

1. ssldir is inside confdir - The default location is in the $confdir/ssl on all platforms.
2. Other stuff in /etc/puppetlabs - Other configs are in /etc/puppetlabs directory. Puppet Server now uses /etc/puppetlabs/puppetserver, and MCollective uses /etc/puppetlabs/mcollective.

• New codedir holds all modules(1), manifests(1) and data(2) - The default codedir location is /etc/puppetlabs/code on *nix. It has environments, modules directories and hiera.yaml config file.

1. Directory environments are always on - The default environmentpath is $codedir/environments and a directory is created at install for the default production environment. Modules are in $codedir/environments/production/modules and main manifest is in $codedir/environments/production/manifests. However you can still use global modules in $codedir/modules and a global manifest.
2. Hiera data goes in environments by default - Hiera’s default settings now use an environment-specific datadir for the YAML and JSON backends. So the production environment’s default Hiera data directory would be /etc/puppetlabs/code/environments/production/hieradata

• Some other directories have moved - The system vardir for puppet agent has moved, and is now separate from Puppet Server’s vardir. For *nix: /opt/puppetlabs/puppet/cache. The rundir, where the service PID files are kept, (on *nix) has moved to /var/run/puppetlabs. (Puppet Server has a puppetserver directory in this directory.)

Reference:
[1] https://docs.puppet.com/puppet/latest/reference/whered_it_go.html