Supports both request proxy and packet forwarding modes. Provides multiple traffic distribution algorithms including round robin, weighted round robin, consistent hashing (packet forwarding), port-based consistent hashing (packet forwarding), source IP, port-based source IP (packet forwarding), and least connections (request proxy). Supports HTTP and HTTPS protocols for Layer 7, and TCP and UDP for Layer 4.

ULB allows customization of idle timeout duration by adjusting the connection timeout parameter. For example, in scenarios where establishing a TCP connection is costly — such as mobile clients that often need to maintain idle connections due to unstable signals — reconnecting can be time-consuming and resource-intensive. In such cases, you can contact UCloud to modify the client idle timeout of ULB to avoid reconnection. The supported timeout range is 1–86400 seconds.

Provides HTTP session persistence. Once enabled, requests from users matching specific characteristics are forwarded to a designated backend host, and subsequent requests from those users remain bound to the same host. Supports both server-inserted cookies and user-specified cookies.

Performs health checks on backend servers based on configured rules, automatically isolating abnormal hosts. Once an issue is detected, the problematic resource is quickly switched out to ensure service availability.

Provides monitoring metrics including current connections, new connections per second, HTTP error code counts, and inbound/outbound bandwidth for EIPs bound to the ULB.

The ULB cluster ensures high availability through built-in health checks and cross-availability-zone disaster recovery.

Packet forwarding mode supports tens of millions of concurrent connections and over 10 Gbps throughput. Request proxy mode integrates application-layer processing capabilities including SSL offloading, domain-based forwarding, and path-based forwarding, supporting hundreds of thousands of concurrent connections and near-Gbps throughput.