Listeners for your Network Load Balancers - Elastic Load Balancing

Listeners for your Network Load Balancers

A listener is a process that checks for connection requests, using the protocol and port that you configure. Before you start using your Network Load Balancer, you must add at least one listener. If your load balancer has no listeners, it can't receive traffic from clients. The rule that you define for a listener determines how the load balancer routes requests to the targets that you register, such as EC2 instances.

Listener configuration

Listeners support the following protocols and ports:

  • Protocols: TCP, TLS, UDP, TCP_UDP

  • Ports: 1-65535

You can use a TLS listener to offload the work of encryption and decryption to your load balancer so that your applications can focus on their business logic. If the listener protocol is TLS, you must deploy exactly one SSL server certificate on the listener. For more information, see TLS listeners for your Network Load Balancer.

If you must ensure that the targets decrypt TLS traffic instead of the load balancer, you can create a TCP listener on port 443 instead of creating a TLS listener. With a TCP listener, the load balancer passes encrypted traffic through to the targets without decrypting it.

To support both TCP and UDP on the same port, create a TCP_UDP listener. The target groups for a TCP_UDP listener must use the TCP_UDP protocol.

For dualstack Network Load Balancers, only TCP and TLS protocols are supported.

You can use WebSockets with your listeners.

All network traffic sent to a configured listener is classified as intended traffic. Network traffic that does not match a configured listener is classified as unintended traffic. ICMP requests other than Type 3 are also considered unintended traffic. Network Load Balancers drop unintended traffic without forwarding it to any targets. TCP data packets sent to the listener port for a configured listeners that are not new connections or part of an active TCP connection are rejected with a TCP reset (RST).

For more information, see Request routing in the Elastic Load Balancing User Guide.

Listener rules

When you create a listener, you specify a rule for routing requests. This rule forwards requests to the specified target group. To update this rule, see Update a listener for your Network Load Balancer.