If anyone's still interesting in this topic, here is the brief instruction:
Download pfsense ISO Create a FreeBSD x64 VM in VirtualBox with PAE/NX, VMDK hard drive on IDE controller, disable audio and usb; attach the ISO to the VM Boot the VM and install pfsense on the virtual hard drive After installation completed, let the VM start rebooting and power it off Create an OS bucket in OCI and upload the VMDK into the bucket Switch to Compute/Instances/Custom Images and import the VMDK image from the bucket From now you can create an instance from the custom image