Help Center/ Elastic Load Balance/ User Guide (Kuala Lumpur Region)/ Getting Started/ Using Load Balancers (Entry Level)
Updated on 2024-04-19 GMT+08:00
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Using Load Balancers (Entry Level)

Scenarios

You have a web application, which often needs to handle heavy traffic and is deployed on two ECSs for load balancing.

You can create a load balancer to distribute traffic evenly across the two ECSs, which eliminates SPOFs and makes your application more available.

Prerequisites

To ensure normal communications between the load balancer and backend servers, you need to check the security group rules and network ACL rules configured for the backend servers.

When backend servers receive requests from the load balancer, source IP addresses are translated into those in 100.125.0.0/16.

  • Security group rules must allow traffic from the 100.125.0.0/16 to backend servers.
  • Network ACL rules are optional for subnets. If network ACL rules are configured for the backend subnet of the load balancer, the network ACL rules must allow traffic from the backend subnet of the load balancer to the backend servers.

If Transfer Client IP Address is enabled for the TCP or UDP listeners, network ACL rules and security group rules will not take effect. You can use access control to limit which IP addresses are allowed to access the listener.

Creating ECSs

ECSs are used as backend servers.

Each ECS needs an EIP for accessing the Internet, and the EIP is used for configuring the application on the ECS. You can determine whether to bind an EIP to the load balancer based on your requirements.

  1. Log in to the management console.
  2. In the upper left corner of the page, click and select the desired region and project.
  3. Hover on in the upper left corner to display Service List and choose Computing > Elastic Cloud Server.

  4. Click Create ECS, configure the parameters, and click Create Now.

    The following table lists the specifications of the two ECSs.
    Table 1 ECS specifications

    Item

    Example Value

    Name

    ECS01 and ECS02

    OS

    CentOS 7.2 64bit

    vCPUs

    2

    Memory

    4 GiB

    System disk

    40 GiB

    Data disk

    100 GiB

    Bandwidth

    5 Mbit/s
  5. Submit your request.

Deploying the Application

Deploy Nginx on the two ECSs and edit two HTML pages so that a page with message "Welcome to ELB test page one!" is returned when ECS01 is accessed, and the other page with message "Welcome to ELB test page two!" is returned when ECS02 is accessed.

  1. Log in to the ECSs.
  2. Install and start Nginx.
    1. Run the wget command to download the Nginx installation package for your operating system in use. CentOS 7.6 is used as an example here. 
      wget http://nginx.org/packages/centos/7/noarch/RPMS/nginx-release-centos-7-0.el7.ngx.noarch.rpm
    2. Run the following command to create the Nginx yum repository: 
      rpm -ivh nginx-release-centos-7-0.el7.ngx.noarch.rpm
    3. Run the following command to install Nginx: 
      yum -y install nginx
    4. Run the following commands to start Nginx and configure automatic Nginx enabling upon ECS startup: 
      systemctl start nginx
systemctl enable nginx
    5. Enter http://EIP bound to the ECS in the address box of your browser. If the following page is displayed, Nginx has been installed.
      Figure 1 Nginx installed successfully
  3. Modify the HTML page of ECS01.
    Modify the index.html file in the default root directory of Nginx /usr/share/nginx/html to identify access to ECS01.
    1. Open the index.html file.

      vim /usr/share/nginx/html/index.html

    2. Press i to enter editing mode.
    3. Modify the index.html file to be as follows: 
       ...
    <body>
        <h1>Welcome to <strong>ELB</strong> test page one!</h1>

        <div class="content">
            <p>This page is used to test the <strong>ELB</strong>!</p>

            <div class="alert">
                <h2>ELB01</h2>
                <div class="content">
                    <p><strong>ELB test (page one)!</strong></p>
                    <p><strong>ELB test (page one)!</strong></p>
                    <p><strong>ELB test (page one)!</strong></p>
                </div>
            </div>
        </div>
    </body>
    4. Press Esc to exit editing mode. Then, enter :wq to save the settings and exit the file.
  4. Modify the HTML page of ECS02.
    Modify the index.html file in the default root directory of Nginx /usr/share/nginx/html to identify access to ECS02.
    1. Open the index.html file.

      vim /usr/share/nginx/html/index.html

    2. Press i to enter editing mode.
    3. Modify the index.html file to be as follows: 
      ...
    <body>
        <h1>Welcome to <strong>ELB</strong> test page two!</h1>

        <div class="content">
            <p>This page is used to test the <strong>ELB</strong>!</p>

            <div class="alert">
                <h2>ELB02</h2>
                <div class="content">
                    <p><strong>ELB test (page two)!</strong></p>
                    <p><strong>ELB test (page two)!</strong></p>
                    <p><strong>ELB test (page two)!</strong></p>
                </div>
             </div>
        </div>
    </body>
    4. Press Esc to exit editing mode. Then, enter :wq to save the settings and exit the file.
  5. Use your browser to access http://ECS01 EIP and http://ECS02 EIP to verify that Nginx has been deployed.

    If the modified HTML pages are displayed, Nginx has been deployed.

    • HTML page of ECS01
      Figure 2 Nginx successfully deployed on ECS01
    • HTML page of ECS02
      Figure 3 Nginx successfully deployed on ECS02

Creating a Load Balancer

The load balancer needs an EIP to access the application deployed on the ECSs over the Internet. You can determine whether to bind an EIP to the load balancer based on your requirements. For details, see Load Balancing on a Public or Private Network.

  1. In the upper left corner of the page, click and select the desired region and project.
  2. Hover on in the upper left corner to display Service List and choose Network > Elastic Load Balance.
  3. Click Create Elastic Load Balancer and then configure the parameters.
  4. Click Create Now.
  5. Confirm the configuration and submit your request.
  6. View the newly created load balancer in the load balancer list.

Adding a Listener

Add a listener to the created load balancer. When you add the listener, create a backend server group, configure a health check, and add the two ECSs to the created backend server group.

Figure 4 Traffic forwarding
  1. Hover on in the upper left corner to display Service List and choose Network > Elastic Load Balance.
  2. Locate the created load balancer (elb-01) and click its name.
  3. Under Listeners, click Add Listener.
  4. Configure the parameters as follows:
    • Name: Enter a name, for example, listener-HTTP.
    • Frontend Protocol: Select a protocol, for example, HTTP.
    • Frontend Port: Enter a port, for example, 80.
  5. Click Next: Configure Request Routing Policy, select or create a backend group, and select a load balancing algorithm.
    • Backend Server Group: Select Use existing or Create new.

      Here we create a backend server group named server_group-ELB.

    • Load Balancing Algorithm: Select an algorithm that the load balancer will use to route requests, for example, Weighted round robin.
  6. Click Next: Add Backend Server and enable the health check.

    Configure the health check as follows:

    • Protocol: Select a protocol for the load balancer to perform health checks on backend servers. If the load balancer uses TCP, HTTP, or HTTPS to receive requests, the health check protocol can be TCP or HTTP. Here we use HTTP as an example.
    • Domain Name: Enter a domain name that will be used for health checks, for example, www.example.com.
    • Health Check Port: Enter a port for the load balancer to perform health checks on backend servers, for example, 80.

      If you do not specify a health check port, the backend port will be used for health checks by default. If you specify a port, it will be used for health check.

  7. Click Next: Confirm, confirm the configurations, and click Submit.
  8. On the Listeners tab, locate the target listener. In the Default Backend Server Group column, click View/Add Backend Server.
  9. On the Backend Servers tab, click the Backend Servers tab and click Add on the top right.
  10. Select the servers you want to add, set the backend port, and click Finish.
    • Backend servers: Select ECS01 and ECS02.
    • Backend port: Set it to 80. Backend servers will use this port to communicate with the load balancer.

Verifying Load Balancing

After the load balancer is configured, you can access the domain name to check whether the two ECSs are accessible.

  1. Modify the C:\Windows\System32\drivers\etc\hosts file on your PC to map the domain name to the load balancer EIP.
    View the load balancer EIP on the Summary page of the load balancer.
    Figure 5 hosts file on your PC
  2. On the CLI of your PC, run the following command to check whether the domain name is mapped to the load balancer EIP:

    ping www.example.com

    If data packets are returned, the domain name has been mapped to the load balancer EIP.

  3. Use your browser to access http://www.example.com. If the following page is displayed, the load balancer has routed the request to ECS01.
    Figure 6 Accessing ECS01
  4. Use your browser to access http://www.example.com. If the following page is displayed, the load balancer has routed the request to ECS02.
    Figure 7 Accessing ECS02
Parent topic: Getting Started