Adding a UDP Listener

Scenarios

You can add a UDP listener, if quick response is required but low reliability is acceptable. UDP listeners are suitable for scenarios such as video chat, gaming, and real-time financial quotations.

Constraints

• UDP listeners do not support fragmentation.
• The port of UDP listeners cannot be 4789.
• UDP packets can have any size less than 1,500 bytes. The packets will be discarded if they are bigger than 1,500 bytes. To avoid this, you need to modify the configuration files of the applications based on the maximum transmission unit (MTU) value.
• Dedicated load balancers: The backend protocol can be UDP or QUIC if the frontend protocol is UDP.
• If you only select the application load balancing type for your dedicated load balancer, you cannot add a UDP listener to this load balancer.

Procedure

1. Go to the load balancer list page.
2. On the displayed page, locate the load balancer and click its name.
3. Under Listeners, click Add Listener. Configure the parameters based on Table 1.

   Table 1 Parameters for configuring a UDP listener

   Parameter	Description
   Name	Specifies the listener name.
   Frontend Protocol	Specifies the protocol that will be used by the load balancer to receive requests from clients. Select UDP.
   Forwarding by Port Ranges	This option is available only for TCP or UDP listeners of a dedicated load balancer. It cannot be disabled after it is enabled. If this option is enabled, the listener listens to requests from all ports in the port range you specify and routes the requests to the corresponding ports on the backend servers. NOTE: This function is available in certain regions. You can see which regions support this function on the console.
   Frontend Port	Specifies the port that will be used by the load balancer to receive requests from clients. The port number ranges from 1 to 65535. NOTE: If you enable Forwarding by Port Ranges, you need to enter a start and end port number as the port range.
   Access Control	Specifies how access to the listener is controlled. For details, see What Is Access Control? The following options are available: All IP addresses Blacklist Whitelist
   IP Address Group	Specifies the IP address group associated with a whitelist or blacklist. If there is no IP address group, create one first. For more information, see IP Address Group.
   Transfer Client IP Address	Specifies whether to transmit IP addresses of the clients to backend servers. This function is enabled for dedicated load balancers by default and cannot be disabled.
   Advanced Settings
   Idle Timeout	Specifies the length of time for a connection to keep alive, in seconds. If no request is received within this period, the load balancer closes the connection and establishes a new one with the client when the next request arrives. The idle timeout duration ranges from 10 to 4000.
   Maximum New Connections per AZ	Specifies the maximum number of new connections that a listener can handle per second in each AZ. The default value is Unlimited. You can select Limit request to set the maximum number of new connections. The value ranges from 1 to 1000000. If the value is greater than the number defined in the load balancer specifications, the latter is used as the limit. NOTE: This option is available in certain regions. You can see which regions support this option on the console.
   Maximum Concurrent Connections per AZ	Specifies the maximum number of concurrent connections that a listener can handle per second in each AZ. The default value is Unlimited. You can select Limit request to set the maximum number of concurrent connections. The value ranges from 1 to 1000000. If the value is greater than the number defined in the load balancer specifications, the latter is used as the limit. Reducing the concurrent connection limit do not interrupt established connections. NOTE: This option is available in certain regions. You can see which regions support this option on the console.
   Tag	Adds tags to the listener. Each tag is a key-value pair, and the tag key is unique.
   Description	Provides supplementary information about the listener. You can enter a maximum of 255 characters.

4. Click Next: Configure Request Routing Policy.
   1. You are advised to select an existing backend server group.
   2. You can also click Create new to create a backend server group.
      1. Configure the backend server group based on Table 3.
      2. Click Next: Add Backend Server. Add backend servers and configure health check for the backend server group.

         For details about how to add backend servers, see Backend Server Overview. For the parameters required for configuring a health check, see Table 4.

5. Click Next: Confirm.
6. Confirm the configurations and click Submit.