This is the database component of the stack.
You can interact with it in vagrant commands by targeting it as "db-vm". Eg:
vagrant up db-vm
vagrant ssh db-vm
See vagrantup.com for more details on how vagrant interacts with multi machines.
It gets assigned the IP 192.168.56.3 which is accessible from your host when using VirtualBox. A DNS entry makes db-vm.codeenigma.com and any subdomain point to it, meaning you can access it at whatever.db-vm.codeenigma.com directly.
When using Docker, it is only accessible through port forwarding, which means you need to add an host entry pointing to 127.0.0.1 to access it through a domain name.
It bundles together: