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    Server Load Balancer:Add a UDP listener

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    Server Load Balancer:Add a UDP listener

    Last Updated:Nov 08, 2024

    If you want your Classic Load Balancer (CLB) instance to forward UDP requests in scenarios that have high requirements for time efficiency but can tolerate relatively lower reliability, such as video conferencing and real-time push of financial information, you can create a UDP listener for your CLB instance.

    Background information

    Before you add a UDP listener, take note of the following items:

    • You cannot specify port 250, port 4789, or port 4790 for UDP listeners. They are reserved by the system.

    • Fragmentation is not supported.

    • If you add a UDP listener to a CLB instance deployed in the classic network, the UDP listener cannot pass client IP addresses to backend servers.

    • The following operations take effect 5 minutes after they are performed on a UDP listener:

      • Remove backend servers.

      • Set the weight of a backend server to 0 after it is declared unhealthy.

    • IPv6 packets have longer IP headers than IPv4 packets. If an IPv6 CLB instance uses a UDP listener, make sure that the maximum transmission unit (MTU) supported by the network interface controller (NIC) that a backend server uses to communicate with CLB is equal to or greater than 1,200 bytes. Otherwise, oversized packets may be discarded. You must modify the MTU setting in the configuration files of some applications accordingly.

      TCP supports Maximum Segment Size (MSS) announcement. Therefore, when you use a TCP, HTTP, or HTTPS listener, you do not need to perform additional configurations.

    Prerequisites

    A CLB instance is created. For more information, see Create and manage a CLB instance.

    Step 1: Add a UDP listener

    1. Log on to the CLB console.

    2. In the top navigation bar, select the region where the CLB instance is deployed.

    3. Use one of the following methods to open the listener configuration wizard:

      • On the Instances page, find the CLB instance that you want to manage and click Configure Listener in the Actions column.

      • On the Instances page, find the CLB instance that you want to manage and click the ID of the instance. On the Listener tab, click Add Listener.

    4. Configure the following parameters and click Next.

      Parameter

      Description

      Listener Protocol

      In this example, UDP is selected.

      Backend Protocol

      In this example, UDP is selected, and the backend protocol is UDP.

      Listener Port

      Specify the listener port that is used to receive and forward requests to backend servers. Valid values: 1 to 65535.

      Listener Name

      Enter a name for the listener.

      Tag

      Select or enter a tag key and a tag value.

      Advanced Settings

      Click Modify to configure advanced settings.

      Scheduling Algorithm

      Select a scheduling algorithm.

      • Weighted Round-robin (WRR): Backend servers that have higher weights receive more requests than backend servers that have lower weights.

      • Round Robin (RR): Requests are sequentially distributed to backend servers.

      • Consistent Hash (CH):

        • QUIC ID: specifies consistent hashing that is based on Quick UDP Internet Connections (QUIC) IDs. Requests that contain the same QUIC ID are distributed to the same backend server.

          Important

          QUIC is implemented based on draft-ietf-quic-transport-10 and iterates rapidly. Therefore, compatibility is not guaranteed for all QUIC versions. We recommend that you perform tests before you apply the protocol to a production environment.

        • Four-element: specifies consistent hashing that is based on four factors: source IP address, destination IP address, source port, and destination port. Requests that contain the same information based on the four factors are distributed to the same backend server.

        • Source IP: specifies consistent hashing that is based on source IP addresses. Requests from the same source IP address are distributed to the same backend server.

      Session Persistence

      Specify whether to enable session persistence.

      After session persistence is enabled, the CLB instance forwards all requests from a client to the same backend server.

      Access Control

      Specify whether to enable access control.

      Select an access control method after you enable access control. Then, select an access control list (ACL) that is used as the whitelist or blacklist of the listener.

      • Whitelist: allows access from specific IP addresses. Only requests from the IP addresses or CIDR blocks specified in the network ACL are forwarded. Whitelists apply to scenarios in which you want to allow access only from specific IP addresses. Your service may be adversely affected if the whitelist is not properly configured. After a whitelist is configured, only requests from IP addresses that are added to the whitelist are forwarded by the listener.

        If a whitelist is configured but no IP address is added to the whitelist, the listener forwards all requests.

      • Blacklist: denies access from specific IP addresses. Requests from the IP addresses or CIDR blocks specified in the network ACL are denied. Blacklists apply to scenarios in which you want to deny access from specific IP addresses.

        If a blacklist is configured but no IP address is added to the blacklist, the listener forwards all requests.

      Note

      IPv6 CLB instances can be associated only with IPv6 ACLs. IPv4 CLB instances can be associated only with IPv4 ACLs. For more information, see Create an ACL.

      Bandwidth Throttling for Listeners

      Specify whether to set a maximum bandwidth for the listener.

      If a pay-by-bandwidth CLB instance is used, you can set a maximum bandwidth for each listener to limit the amount of network traffic forwarded by listeners. The sum of the maximum bandwidth of all listeners that are added to a CLB instance cannot exceed the maximum bandwidth of the CLB instance. By default, this feature is disabled and all listeners share the bandwidth of the CLB instance.

      Important

      • For example, the maximum bandwidth of an Internet-facing CLB instance is 5 Mbit/s, and you configure two listeners. You allocate 5 Mbit/s of bandwidth to Listener A, and do not allocate bandwidth to Listener B. In this case, Listener B is inaccessible. Exercise caution when you allocate bandwidth.

      • If three listeners are configured for an internal-facing CLB instance, and the total bandwidth allocated to Listener A and Listener B is 5,120 Mbit/s, Listener C is inaccessible. Exercise caution when you allocate bandwidth.

      • If a pay-by-data-transfer CLB instance is used, the bandwidth of listeners is unlimited by default.

      Proxy Protocol

      Specify whether to use the Proxy protocol to pass client IP addresses to the backend servers.

      Note

      You cannot enable this feature if PrivateLink is used.

      Obtain Client Source IP Address

      Specify whether to reserve the IP addresses of clients. Only Layer 4 listeners support this feature. By default, this feature is enabled.

      Note

      If the UDP listener is added to a CLB instance deployed in the classic network, you can enable Proxy Protocol to obtain client IP addresses.

      Automatically Enable Listener

      Specify whether to immediately enable the listener after it is created. By default, listeners are enabled after they are created.

    Step 2: Add backend servers

    After you configure the listener, you must add backend servers to process client requests. You can use the default server group that is configured for the CLB instance. You can also configure a vServer group or a primary/secondary server group. For more information, see Backend server overview.

    1. In the Backend Servers step, select the type of the backend server group to which requests are forwarded. In this example, the default backend server group is used.

      Select Default Server Group and click Add More.

    2. In the Servers step, select the Elastic Compute Service (ECS) instances that you want to add and click Next.

    3. In the Ports/Weights step, configure the weights of the backend servers. ECS instances that have higher weights receive more requests.

      Note

      If the weight of a backend server is set to 0, no request is distributed to the backend server.

    4. Click Add. Specify the port that is used by the backend server to receive requests. Valid values: 1 to 65535.

      You can specify the same port for backend servers that are added to the same CLB instance.

    5. Click Next.

    Step 3: Configure health checks

    CLB checks the availability of backend servers by performing health checks. The health check feature improves overall service availability and reduces the impact of backend server failures.

    Note

    You cannot disable health checks for a listener that is associated with a primary/secondary server group.

    1. Optional: In the Health Check step, click Modify to modify the health check configuration.

      For more information, see Configure and manage CLB health checks.

    2. Click Next.

    Step 4: Submit the configurations

    1. In the Confirm step, check the configurations of the listener. You can click Modify to modify the configurations.

    2. Confirm the configurations and click Submit.

    3. In the Configuration Successful message, click OK.

      After you configure the listener, you can view the listener on the Listener tab.