Can all the instances in a VPC can ping each other by default?
Thereof, can instances in the same security group talk to each other?
Instances associated with the same security group can't talk to each other unless you add rules allowing it (with the exception being the default security group). you have to add rules to make them able to communicate.
One may also ask, can AWS subnets communicate with each other? When you create new subnets within a custom VPC, by default they can communicate with each other, across availability zones. When you create new subnets within a custom VPC, by default they can communicate with each other, across availability zones.
In this regard, how many ec2 instances can be used in a VPC?
You can run any number of Amazon EC2 instances within a VPC, so long as your VPC is appropriately sized to have an IP address assigned to each instance. You are initially limited to launching 20 Amazon EC2 instances per VPC at any one time and a maximum VPC size of /16 (65,536 IPs).
Can you attach a network interface in one VPC to an instance in another VPC?
Network interfaces can only be attached to instances in the same VPC as the interface.