Reading here talks about the ENI (Elastic Network Interface). Do I need to create these manually when using the Global Accelerator, or what do I need to do in regards to ENIs?
Do I need to manually create ENIs, or are they created automatically, when using Global Accelerator? If manual, do I connect them with instances or what do I connect them to?
They are automatically created when the Global Accelerator is created.
The ENI is the way that resources connect into the VPC. ENIs are also used by EC2, Lambda, RDS, Redshift, etc.
This documentation page will help answer your questions:
How Global Accelerator uses elastic network interfaces
When you have an Application Load Balancer with client IP address preservation enabled, the number of subnets that the load balancer is in determines the number of elastic network interfaces that Global Accelerator creates in your account. Global Accelerator creates one elastic network interface for each subnet that has at least one elastic network interface of the Application Load Balancer in it that is fronted by an accelerator in your account.
The following examples illustrate how this works:
Example 1: If an Application Load Balancer has elastic network interfaces in subnetA and subnetB, and then you add the load balancer as an accelerator endpoint, Global Accelerator creates two elastic network interfaces, one in each subnet.
Example 2: If you add, for example, an ALB1 that has elastic network interfaces in subnetA and subnetB to Accelerator1, and then add an ALB2 with elastic network interfaces in subnetA and subnetB to Accelerator2, Global Accelerator creates only two elastic network interfaces: one in subnetA and one in subnetB.
Example 3: If you add an ALB1 that has elastic network interfaces in subnetA and subnetB to Accelerator1, and then add an ALB2 with elastic network adaptors in subnetA and subnetC to Accelerator2, Global Accelerator creates three elastic network interfaces: one in subnetA, one in subnetB, and one in subnetC. The elastic network interface in subnetA delivers traffic on for both Accelerator1 and Accelerator2.
As shown in Example 3, elastic network interfaces are reused across accelerators if endpoints in the same subnet are placed behind multiple accelerators.
The logical elastic network interfaces that Global Accelerator creates do not represent a single host, a throughput bottleneck, or a single point of failure. Like other AWS services that appear as a single elastic network interface in an Availability Zone or subnet—services like a network address translation (NAT) gateway or a Network Load Balancer—Global Accelerator is implemented as a horizontally scaled, highly available service.
Evaluate the number of subnets that are used by endpoints in your accelerators to determine the number of elastic network interfaces that Global Accelerator will create. Before you create an accelerator, make sure that you have enough IP address space capacity for the required elastic network interfaces, at least one free IP address per relevant subnet. If you don't have enough free IP address space, you must create or use a subnet that has adequate free IP address space for your Application Load Balancer and associated Global Accelerator elastic network interfaces.
When Global Accelerator determines that an elastic network interface is not being used by any of the endpoints in accelerators in your account, Global Accelerator deletes the interface.
