When you created the 'opencti' stack (or whatever you called it), it'll create a default network (opencti_default). This defines an internal IP range used by docker containers assigned to that network. DHCP is used by default, so you need to remember that if you're going to refer to your OpenCTI host by hostname and not IP address, you need to ensure your DNS settings are configured correctly so the hostname will resolve. That's outside the scope of this guide. If you want to follow along with this guide, just be sure to set a static IP address for your OpenCTI container.