I have amazon VPC set through wizard as \"public only network\", so all my instances are in public subnet.
Instances within VPC that have Elastic IP assigned connect
Instances without EIPs can access the Internet in one of two ways Instances without EIPs can route their traffic through a NAT instance to access the Internet. These instances use the EIP of the NAT instance to traverse the Internet. The NAT instance allows outbound communication but doesn’t enable machines on the Internet to initiate a connection to the privately addressed machines using NAT.
https://docs.aws.amazon.com/vpc/latest/userguide/VPC_NAT_Instance.html