One DirectConnect with both Private and Public VIF

It is possible to use a single AWS DirectConnect connection to configure both Private and public VIFs.

but you need to consider

• they share bandwidth so ensure the connection capacity is enough for you
• Implement separate routing and security measures for Private and Public VIFs
• Using a single connection for both types of VIFs introduces a single point of failure. Consider redundancy

Yes you can combine both Public and Private VIFs on the same dedicated Direct Connect. How are you planning to use the Public VIF? Watch the requirements for Public VIF is a bit different. It will require you to allocate Public IPv4 CIDR to establish the p2p public VIF connection. If you are going to access any services over the Public VIF from your on premises private network, you will need to have some sort of NATing to public IP. You treat this connection as Internet. The prefixes for your NAT or any source with public IP used, will be shared with AWS the time you create the connection to be added to the routing back to your network.