Classic Load Balancer (CLB) provides Layer 4 and Layer 7 load balancing. The tables below list the features supported at each layer. "✔" means supported and "–" means not supported.
Traffic management
| Feature |
Description |
Layer 4 |
Layer 7 |
| Routing algorithms |
CLB supports three algorithms: round-robin (RR), weighted round-robin (WRR), and consistent hashing (CH). Layer 7 does not support CH. |
✔ |
✔ |
| Session persistence |
Routes all requests from the same session to the same backend server. |
✔ |
✔ |
| Domain name-based and URL-based forwarding |
Routes requests to different backend servers based on domain name or URL path. Configured on Layer 7 listeners only. |
– |
✔ |
High availability and security
| Feature |
Description |
Layer 4 |
Layer 7 |
| High availability |
Distributes traffic across zones, with cross-zone deployment supported in most regions. If the primary zone fails, traffic automatically shifts to the secondary zone. |
✔ |
✔ |
| Network access control lists (ACLs) |
Controls access using allowlists and denylists. |
✔ |
✔ |
| DDoS protection |
Integrates with Apsara Stack Security to protect against DDoS attacks of up to 5 Gbit/s. |
✔ |
✔ |
| Certificate management |
Centrally manages certificates for HTTPS listeners. CLB decrypts requests before forwarding them to backend servers, reducing backend processing load. |
– |
✔ |
| Server Name Indication (SNI) |
Associates multiple certificates with a single HTTPS listener to route requests from different domain names to different backend servers. |
– |
✔ |
| HTTP-to-HTTPS redirection |
Redirects HTTP requests to HTTPS. |
– |
✔ |
Protocols and network
| Feature |
Description |
Layer 4 |
Layer 7 |
| Network types |
Supports Internet-facing instances for public traffic and internal-facing instances for traffic within a virtual private cloud (VPC). |
✔ |
✔ |
| IPv6 support |
Forwards requests from IPv6 clients to IPv4 backend servers. IPv6 backend servers are not supported. |
✔ |
✔ |
| WebSocket (WS) and WebSocket Secure (WSS) |
Supports full-duplex communication between clients and servers. |
– |
✔ |
| HTTP/2 |
Supports HTTP/2, which is backward compatible with HTTP/1.X. |
– |
✔ |
Monitoring and logging
| Feature |
Description |
Layer 4 |
Layer 7 |
| Health checks |
Monitors the health of backend servers and stops routing traffic to unhealthy servers. |
✔ |
✔ |
| Monitoring |
Provides connection counts and the volumes of inbound and outbound traffic through CloudMonitor. |
✔ |
✔ |
| Health check logs |
Retains health check logs for the last 3 days by default. To store all logs, enable Object Storage Service (OSS) first. |
✔ |
✔ |