Getting Started with CLB

Last updated: 2020-05-22 14:42:36

    Tencent Cloud CLB supports the TCP, UDP, TCP SSL, HTTP, and HTTPS protocols and provides flexible forwarding capabilities based on domain names and URL paths. This document guides you through how to get started with CLB.


    1. CLB only forwards traffic but cannot process requests; therefore, you need to have a CVM instance that processes user requests.
      In this example, two CVM instances are enough, but you can also configure more instances. CVM instances rs-1 and rs-2 have been created in the Guangzhou region in this example. For more information on how to create a CVM instance, please see Purchasing and Launching CVM Instances.
    2. This document takes HTTP forwarding as an example. The corresponding web server (such as Apache, Nginx, or IIS) must be deployed on the CVM instance.
      To verify the result, in this example, Nginx is deployed on both rs-1 and rs-2. Nginx returns "Hello nginx! This is rs-1!" on rs-1 and "Hello nginx! This is rs-2!" on rs-2. For more information on how to deploy components on a CVM instance, please see Deploying Java Web on Linux (CentOS) and Installing and Configuring PHP on Windows.
    3. Access the public IP and path of your CVM instances. If the deployed page is displayed, the service has been successfully deployed.
      • Public network bandwidth must be purchased for the CVM instances, as the bandwidth is billed by CVM rather than CLB.
      • In this example, the values returned by the service deployed on two real servers are different. In actual scenarios, to ensure that all users have a uniform experience, generally the same service should be deployed on all real servers.

    Purchasing CLB Instance

    After a CLB instance is successfully purchased, the system will automatically assign it a VIP, through which CLB provides service to clients.

    1. Log in to Tencent Cloud's official website and go to the CLB purchase page.
    2. In this example, select Guangzhou as the region, which is the same as that of the CVM instances. Select CLB as the instance type, Public Network as the network attribute, and Default-VPC (Default) as the network and enter clb-test as the instance name.
    3. Click Buy Now and make the payment.
      For more information on CLB instances, please see Product Attribute Selection.
    4. On the "CLB Instance List" page, select the corresponding region to view the instance just created.

    Creating CLB Listener

    A CLB listener forwards requests by specifying protocols and ports. This document takes configuration of forwarding HTTP client requests by CLB as an example.

    Configuring HTTP listener protocol and port

    When a client sends a request, CLB will receive the request according to the listened frontend protocol and port and forward it to the real server.

    1. Log in to the CLB Console.
    2. On the instance management page, find the created CLB instance clb-test and click its ID to enter its details page.
    3. In the "Basic Info" module, you can click the modification icon next to the instance name to rename it.
    4. In HTTP/HTTPS Listeners in "Listener Management", click Create to create a CLB listener.
    5. In the pop-up box, configure the following:
      • Set the name to "Listener1".
      • Set the listener protocol and port to HTTP:80.
    6. Click Submit to create the CLB listener.

    Configuring listener forwarding rule

    When a client sends a request, CLB will forward the request according to the configured listener forwarding rule.

    1. On the "Listener Management" page, select the new listener "Listener1" and click + to add a rule.
    2. In the pop-up box, configure the domain name, URL path, and balancing method.
      • Domain Name: it is the domain name used by your real server, which can contain a wildcard. In this example, is used. For more information, please see Configuration Description.
      • Default Domain Name: if a client request cannot be matched with any domain name of this listener, CLB will forward the request to the default domain name (default server). Each listener can be configured with only one default domain name. If a listener has not been configured with a default domain name, CLB will forward the request to the first domain name. In this example, this field is not configured.
      • URL Path: it is the access path of your real server. /image/ is used in this example.
      • Select "WRR" as the load balancing mode.
    3. Configure health check: enable health check and check the default forwarded domain name and path used by the domain name.
    4. Session Persistence: do not check this option.
    5. Click Finish to complete the listener forwarding rule configuration.

    For more information on CLB listeners, please see CLB Listener Overview.

    • A listener (i.e., listening protocol:port) can be configured with multiple domain names, and a domain name can be configured with multiple URL paths. Select a listener or domain name and click + to create a new rule.
    • Session persistence: if session persistence is disabled and a round-robin method is used for scheduling, requests will be assigned to different real servers in sequence; if session persistence is enabled, or it is disabled but ip_hash scheduling is used, requests will always be assigned to the same real server.

    Binding CVM instance

    When a client sends a request, CLB will forward the request to the CVM instance bound to the listener for processing.

    1. On the "Listener Management" page, select and expand the listener "Listener1" just created and select the domain name and URL path, and the information of the CVM instance bound to the URL path will be displayed on the right. Click Bind.
    2. In the pop-up box, select CVM as the instance type, select CVM instances rs-1 and rs-2 in the same region as the CLB instance, set the port of the two CVM instances to "80", and keep the default weight "10" for them.
    3. Click OK to complete binding.
    4. Expand the listener to display the URL paths. You can view the bound CVM instances and their health check status. The "Healthy" status indicates that the CVM instance can properly process requests forwarded by CLB.

      A forwarding rule (listener protocol + port + domain name + URL path) can be bound to multiple ports of the same CVM instance. For example, if you deploy the same service on ports 80 and 81 on rs-1, CLB allows you to bind both the ports to the forwarding rule in the example, and both of them will receive the requests forwarded by CLB.

    Verifying CLB Service

    After configuring a CLB instance, you can verify whether the architecture takes effect by checking whether different domain names and URLs under the CLB instance can access different real servers, i.e., checking whether the content-based routing feature is available.

    Method 1. Configure hosts to point the domain name to the CLB instance

    1. On Windows, enter the C:\Windows\System32\drivers\etc directory, modify the hosts file, and map the domain name to the VIP of the CLB instance.
    2. To check whether the hosts is successfully configured, run the ping command on the command line to check whether this domain name is successfully bound to the VIP. If data packets are returned, the binding is successful.
    3. Enter the access path in a browser to test the CLB service. If a message is displayed as shown below, the request has been forwarded to the CVM instance rs-1 by CLB, and the CVM instance has properly processed the request and returned the result.
    4. The round robin algorithm of the listener is "weighted round robin", and the weights of the two CVM instances are both "10". If you refresh the webpage in the browser to send a new request, you can see that the request is forwarded to the CVM instance rs-2 by CLB.

      / at the end of image/ must be retained, which indicates that image is the default directory rather than a file named image.

    Configuring Redirection (Optional)

    Redirection can be performed manually or automatically:

    • Automatic redirection (forced HTTPS): when a PC or mobile browser accesses a web service with an HTTP request, an HTTPS response can be returned to the browser after the request passes through the CLB proxy, forcing the browser to access the webpage over HTTPS.
    • Manual redirection: if you want to temporarily deactivate your web business in cases such as product sellout, page maintenance, or update and upgrade, redirection capabilities will be required. If no redirection is performed, the old address in a visitor's favorites and search engine database will return a 404 or 503 error message page, degrading the user experience and resulting in traffic waste. The SEO score obtained by this page will also become invalid.
      For more information, please see Redirection Configuration.

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