Map one AWS ELB load balancer port to balance to multiple instance ports?

Important Update

The service offering has evolved, so the following information (the original answer) is only applicable to ELB/1.0, which is now called an ELB Classic Load Balancer:

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No, this isn't possible with ELB.

You can map multiple listeners on the front-side of an ELB to hit a single port on the back-end instances, but you can't map a single listener on the font-side of an ELB to hit multiple ports on the back-end instances.

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ELB/2.0, called Application Load Balancer was released in late 2016 and does support multiple instance ports, using "target groups."

It also allows selective request routing by path pattern matching, supports web sockets in HTTP mode, and HTTP/2 on the front side.

When launching a balancer, you can still launch a Classic (it's still available, and the single instance port limit per listener still applies) or you can launch an ALB to get the new functionality.