AWS EC2 Networking

Public IPv4 addresses are lost when the instance is stopped but private addresses (IPv4 and IPv6) are retained Elastic IPs are retained when the instance is stopped.

All accounts are limited to 5 elastic IP's per region by default AWS charge for elastic IP's when they're not being used 

An Elastic IP address is for use in a specific region only You can assign custom tags to your Elastic IP addresses to categorize them 

By default, EC2 instances come with a private IP Public IP addresses are assigned for instances in public subnets (VPC) 

Public IP addresses are always assigned for instances in EC2-Classic DNS records for elastic IP's can be configured by filling out a form 

Secondary IP addresses can be useful for hosting multiple websites on a server or redirecting traffic to a standby EC2 instance for HA

You can choose whether secondary IP addresses can be reassigned 

You can associate a single private IPv4 address with a single Elastic IP address and vice versa 

When reassigned the IPv4 to Elastic IP association is maintained 

When a secondary private address is unassigned from an interface, the associated Elastic IP address is disassociated 

You can assign or remove IP addresses from EC2 instances while they are running or stopped All IP addresses (IPv4 and IPv6) remain attached to the network interface when detached or reassigned to another instance 

You can attach a network interface to an instance in a different subnet as long as it’s within the same AZ 

You cannot team by adding ENIs to an instance Eth0 is the primary network interface and cannot be moved or detached 

By default, Eth0 is the only Elastic Network Interface