Server Load Balancer:Preparations

Select a region to deploy a CLB instance

When you select a region, take note of the following items:

• By default, you cannot deploy a CLB instance across multiple regions. Make sure that the CLB instance and the Elastic Compute Service (ECS) instances that you want to add to the CLB instance belong to the same region.

  For example, if the ECS instance that hosts your services is deployed in the China (Hangzhou) region, you must create a CLB instance in the China (Hangzhou) region. This way, you can add the ECS instance to the CLB instance.

• CLB supports primary/secondary zone deployment in most regions. You can deploy a CLB instance across zones to achieve disaster recovery across data centers in the same region. This ensures service stability and reliability. We recommend that you select a region that supports primary/secondary zone deployment.

Select the type of network to deploy your CLB instance

CLB provides load balancing services over the Internet and the internal network.

• If you want to use CLB to distribute requests from the Internet, create an Internet-facing CLB instance.

  An Internet-facing CLB instance is assigned a public IP address to receive requests from the Internet.

• If you want to use CLB to distribute requests from the internal network, create an internal-facing CLB instance.

  An internal-facing CLB instance uses a private IP address from the IP address pool of Alibaba Cloud to distribute requests within the internal network of Alibaba Cloud. An internal-facing CLB instance cannot distribute requests over the Internet.

Select a specification for your CLB instance

• If your workloads expect only minor fluctuations, we recommend that you select Pay-By-Specification. You are charged a specification fee on an hourly basis.
• If your workloads expect periodic or large fluctuations, we recommend that you select Pay-By-LCU. Pay-by-LCU CLB instances can automatically scale resources on demand. In addition, you do not need to specify a specification. You are charged for consumed LCUs on an hourly basis.

Select a listening protocol

CLB supports Layer 4 load balancing over TCP and UDP and Layer 7 load balancing over HTTP and HTTPS.

• Layer 4 listeners forward requests directly to backend servers. When a CLB instance receives a request, the CLB instance modifies the destination IP address and destination port of the data packet based on the listener port. Then, the CLB instance forwards the request to a backend server. A TCP connection is established between the client and the backend server.
• A Layer 7 listener functions as a reverse proxy. After a client request reaches a Layer 7 listener of CLB, CLB establishes a new TCP connection to a backend server over HTTP, instead of directly forwarding the request to the backend server.

  Compared with Layer 4 listeners, Layer 7 listeners require an additional step of Tengine processing. The throughput capacity of Layer 7 listeners may be limited by factors such as client port exhaustion or excessive workloads on backend servers. If your business requires higher performance, we recommend that you use Layer 4 listeners.

  For more information, see Protocols.

Create backend servers

Before you use the CLB service, you must create ECS instances, deploy applications on the ECS instances, and then add the ECS instances to your CLB instance to process client requests.