How custom routing accelerators work in AWS Global Accelerator

By using a custom routing accelerator in AWS Global Accelerator, you can use application logic to directly map one or more users to a specific destination among many destinations while still gaining the performance benefits of Global Accelerator. A custom routing accelerator maps listener port ranges to EC2 instance destinations in virtual private cloud (VPC) subnets. This allows Global Accelerator to deterministically route traffic to a specific Amazon EC2 private IP address and port destination in your subnet.

For example, you can use a custom routing accelerator with an online real-time gaming application in which you assign multiple players to a single session on an Amazon EC2 game server based on factors that you choose, such as geographic location, player skill, and game mode. Or you might have a VoIP or social media application that assigns multiple users to a specific media server for voice, video, and messaging sessions.

Your application can call a Global Accelerator API and receive a full static mapping of Global Accelerator ports and their associated destination IP addresses and ports. You can save that static mapping, and then your matchmaking service use it to route users to specific destination EC2 instances. You don't have to make any modifications to your client software to start using Global Accelerator with your application.

To configure a custom routing accelerator, you select a VPC subnet endpoint. Then you define a destination port range that incoming connections will be mapped to, so your software can listen on the same set of ports across all instances. Global Accelerator creates a static mapping that allows your matchmaking service to translate a destination IP address and port number for a session to an external IP address and port that you give to users.

Your application’s network stack might operate over a single transport protocol, or you might use UDP for fast delivery and TCP for reliable delivery. You can set UDP, TCP, or both UDP and TCP for each destination port range, to give you maximum flexibility without having to duplicate your configuration for each protocol.

Note

By default, all VPC subnet destinations in a custom routing accelerator aren't allowed to receive traffic. This is to be secure by default, and also to give you granular control over which private EC2 instance destinations in your subnet are allowed to receive traffic. You can allow or deny traffic to the subnet, or to specific IP address and port combinations (destination sockets). For more information, see Adding, editing, or removing a VPC subnet endpoint. You can also specify destinations by using the Global Accelerator API. For more information, see AllowCustomRoutingTraffic and DenyCustomRoutingTraffic.

Example of how custom routing works in Global Accelerator

As an example, let's say that you want to support 10,000 sessions where groups of users interact, such as gaming sessions or VoIP call sessions, across 1,000 Amazon EC2 instances behind Global Accelerator. In this example, we'll specify a listener port range of 10001–20040 and a destination port range of 81–90. We'll say that we have the four VPC subnets in us-east-1: subnet-1, subnet-2, subnet-3, and subnet-4.

In our example configuration, each VPC subnet has a block size of /24 so it can support 251 Amazon EC2 instances. (Five addresses are reserved and unavailable from each subnet, and these addresses are not mapped.) Each server running on each EC2 instance serves the following 10 ports, that we specified for the destination ports in our endpoint group: 81-90. This means that we have 2510 ports (10 x 251) associated with each subnet. Each port can be associated with a session.

Because we've specified 10 destination ports on each EC2 instance in our subnet, Global Accelerator internally associates them with 10 listener ports that you can use to access EC2 instances. To illustrate this simply, we'll say that there's a block of listener ports that starts with the first IP address of the endpoint subnet for the first set of 10, and then moves to the next IP address for the next set of 10 listener ports.

Note

The mapping is actually not predictable like this, but we're using a sequential mapping here to help to show how the port mapping works. To determine the actual mapping for your listener port ranges, use the following API operations: ListCustomRoutingPortMappings and ListCustomRoutingPortMappingsByDestination.

In our example, the first listener port is 10001. That port is associated with the first subnet IP address, 192.0.2.4, and the first EC2 port, 81. The next listener port, 10002, is associated with the first subnet IP address, 192.0.2.4, and the second EC2 port, 82. The following table illustrates how this example mapping continues through the last IP address of the first VPC subnet, and then on to the first IP address of the second VPC subnet.

Global Accelerator listener port	VPC subnet	EC2 instance port
10001	192.0.2.4	81
10002	192.0.2.4	82
10003	192.0.2.4	83
10004	192.0.2.4	84
10005	192.0.2.4	85
10006	192.0.2.4	86
10007	192.0.2.4	87
10008	192.0.2.4	88
10009	192.0.2.4	89
10010	192.0.2.4	90
10011	192.0.2.5	81
10012	192.0.2.5	82
10013	192.0.2.5	83
10014	192.0.2.5	84
10015	192.0.2.5	85
10016	192.0.2.5	86
10017	192.0.2.5	87
10018	192.0.2.5	88
10019	192.0.2.5	89
10020	192.0.2.5	90
...	...	...
12501	192.0.2.244	81
12502	192.0.2.244	82
12503	192.0.2.244	83
12504	192.0.2.244	84
12505	192.0.2.244	85
12506	192.0.2.244	86
12507	192.0.2.244	87
12508	192.0.2.244	88
12509	192.0.2.244	89
12510	192.0.2.244	90
12511	192.0.3.4	81
12512	192.0.3.4	82
12513	192.0.3.4	83
12514	192.0.3.4	84
12515	192.0.3.4	85
12516	192.0.3.4	86
12517	192.0.3.4	87
12518	192.0.3.4	88
12519	192.0.3.4	89
12520	192.0.3.4	90