Using Dedicated Load Balancers (Advanced Level)

Scenarios

You have two web applications that are deployed on separated ECSs but use the same domain name for access. You can set different URLs to process requests.

To forward requests based on URLs, you need to create a load balancer, add an HTTP or HTTPS listener, and add forwarding policies to specify the URLs.

An HTTP listener is used as an example to describe how to route requests from two URLs (/ELB01 and /ELB02) of the same domain name (www.example.com) to different backend servers.

Prerequisites

  • You have added security group rules to allow traffic from the ports used by the two ECSs. (Alternatively, you can enable all ports first and then disable the ports that are no longer used after service deployment.)

  • You have verified that the security group containing the ECSs allows access traffic from the VPC where the load balancer works and that the health check function is normal.

    Note

    If IP as a Backend is not enabled for a dedicated load balancer that has a TCP or UDP listener, there is no need to configure security group rules to allow traffic from the VPC where the load balancer backend subnet works to the backend servers.

Creating ECSs

ECSs are used as backend servers.

Each ECS needs an EIP for accessing the Internet and configuring the application on the ECS.

  1. Log in to the management console.

  2. In the upper left corner of the page, click image1 and select the desired region and project.

  3. Hover on image2 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

    CPU

    2vCPUs

    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: CentOS 7.6 is used as an example here.

      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

      Figure 1 Nginx installed successfully

  3. Modify the HTML page of ECS01.

    Move the index.html file from the default root directory of Nginx /usr/share/nginx/html to the ELB01 directory and modify the file to identify access to ECS01.

    1. Create the ELB01 directory and copy the index.html file to this directory:

      mkdir /usr/share/nginx/html/ELB01

      cp /usr/share/nginx/html/index.html /usr/share/nginx/html/ELB01/

    2. Open the index.html file.

      vim /usr/share/nginx/html/ELB01/index.html

    3. Press i to enter editing mode.

    4. Modify the index.html file.

      The following is the content to be modified:

      ...
   <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>

    5. Press Esc to exit editing mode. Then, enter :wq to save the settings and exit the file.

  4. Modify the HTML page of ECS02.

    Move the index.html file from the default root directory of Nginx /usr/share/nginx/html to the ELB02 directory and modify the file to identify access to ECS02.

    1. Create the ELB02 directory and copy the index.html file to this directory:

      mkdir /usr/share/nginx/html/ELB02

      cp /usr/share/nginx/html/index.html /usr/share/nginx/html/ELB02/

    2. Open the index.html file.

      vim /usr/share/nginx/html/ELB02/index.html

    3. Press i to enter editing mode.

    4. Modify the index.html file.

      The following is the content to be modified:

      ...
    <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>

    5. 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/ELB01/ and http://ECS02 EIP/ELB02/ 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

      Figure 2 Nginx successfully deployed on ECS01

    • HTML page of ECS02

      **Figure 3** Nginx successfully deployed on ECS02

      Figure 3 Nginx successfully deployed on ECS02

Creating a Load Balancer

Each ECS needs an EIP for accessing the Internet and configuring the application on the ECS. 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 image3 and select the desired region and project.

  2. Hover on image4 in the upper left corner to display Service List and choose Network > Elastic Load Balancing.

  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.

Note

After you create a dedicated load balancer, configure the security group that contains the ECSs to allow traffic from the VPC where the load balancer works.

Procedure

  1. Log in to the management console.

  2. In the upper left corner of the page, click image5 and select the desired region and project.

  3. Under Computing, click Elastic Cloud Server.

  4. On the Elastic Cloud Server page, click the name of the ECS that has been added to a backend server group.

    The page providing details about the ECS is displayed.

  5. Click Security Groups, locate the security group, and view security group rules.

  6. Click the security group rule ID or Modify Security Group Rule. The security group details page is displayed.

  7. On the Inbound Rules tab page, click Add Rule. Configure an inbound rule based on Table 2.

    Table 2 Security group rules

    Backend Protocol

    Policy

    Protocol & Port

    Source IP Address

    HTTP or HTTPS

    Allow

    Protocol: TCP

    Port: the port used by the backend server and health check port

    Backend subnet of the load balancer

    TCP

    Allow

    Protocol: TCP

    Port: health check port

    UDP

    Allow

    Protocol: UDP and ICMP

    Port: health check port

    Note

    • After a load balancer is created, do not change the subnet. If the subnet is changed, the IP addresses occupied by the load balancer will not be released, and traffic from the previous backend subnet is still need to be allowed to backend servers.

    • Traffic from the new backend subnet is also need to be allowed to backend servers.

  8. Click OK.

Firewall Rules

To control traffic in and out of a subnet, you can associate a firewall with the subnet. Firewalls rules control access to subnets and add an additional layer of defense to your subnets. The default firewall rule denies all inbound and outbound traffic. If the subnet of a load balancer or associated backend servers has a firewall rule associated, the load balancer cannot receive traffic from the Internet or route traffic to backend servers, and backend servers cannot receive traffic from and respond to the load balancer.

Configure an inbound firewall rule to allow traffic from the VPC where the load balancer resides to backend servers.

  1. Log in to the management console.

  2. In the upper left corner of the page, click image6 and select the desired region and project.

  3. Click image7 in the upper left corner of the page and choose Network > Virtual Private Cloud.

  4. In the navigation pane on the left, choose Access Control > Firewalls.

  5. In the firewall list, click the name of the firewall to switch to the page showing its details.

  6. On the Inbound Rules or Outbound Rules tab page, click Add Rule to add a rule.

    • Action: Select Allow.

    • Protocol: The protocol must be the same as the one you selected for the listener.

    • Source: Set it to the VPC CIDR block.

    • Source Port Range: Select a port range.

    • Destination: Enter a destination address allowed in this direction. The default value is 0.0.0.0/0, which indicates that traffic from all IP addresses is permitted.

    • Destination Port Range: Select a port range.

    • (Optional) Description: Describe the firewall rule if necessary.

  7. Click OK.

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.

Configure two forwarding policies to forward HTTP requests to the two ECSs, for example, requests from www.example.com/ELB01/ to ECS01, and those from www.example.com/ELB02/ to ECS02.

**Figure 4** Traffic forwarding

Figure 4 Traffic forwarding

  1. Hover on image8 in the upper left corner to display Service List and choose Network > Elastic Load Balancing.

  2. Locate the load balancer and click its name.

  3. Under Listeners, click Add Listener.

  4. Configure the listener and click Next.

    • Name: Enter a name, for example, listener-HTTP.

    • Frontend Protocol/Port: Select a protocol and enter a port for the load balancer to receive requests. For example, set it to HTTP and 80.

  5. Create a backend server group, configure a health check, and click Finish.

    • Backend Server Group

      • Name: Enter a name, for example, server_group-ELB.

      • Load Balancing Algorithm: Select an algorithm that the load balancer will use to route requests, for example, Weighted round robin.

    • Health check

      • 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. Note that the protocol cannot be changed after the listener is added.

      • 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.

Adding a Forwarding Policy

  1. Click the name of the newly added listener and then click Add next to Forwarding Policies.

  2. Configure the forwarding policy and click Next.

    • Name: Enter a name for the forwarding policy, for example, forwarding_policy-ELB01.

    • Domain Name: Enter a domain name that will be used to forward the requests, for example, www.example.com. The domain name in the request must exactly match that specified in the forwarding policy.

    • URL: You can also specify a URL to forward the requests, for example, /ELB01/.

    • URL Matching Rule: Select a rule for matching the specified URL string with the URL in the request. Three options are available, Exact match, Prefix match, and Regular expression match. Exact match enjoys the highest priority, and Regular expression match the lowest priority. Select Exact match here.

  3. Create a backend server group, configure a health check, and click Finish.

    • Backend Server Group

      • Name: Enter a name, for example, server_group-ELB01.

      • Load Balancing Algorithm: Select an algorithm that the load balancer will use to route requests, for example, Weighted round robin.

    • Health check

      • 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. Note that the protocol cannot be changed after the listener is added.

      • 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.

  4. Select the newly added forwarding policy. On the Backend Server Groups tab page on the right, click Add.

  5. Select the server you want to add, set the backend port, and click Finish.

    • Backend server: ECS01

    • Backend port: Set it to 80. Backend servers will use this port to communicate with the load balancer.

  6. Repeat the preceding steps to add another forwarding policy, create a backend server group, and add ECS02 to the backend server group.

Verifying Load Balancing

After the load balancer is configured, you can access the domain name or the specified URL 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

    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/ELB01/. If the following page is displayed, the load balancer has routed the request to ECS01.

    **Figure 6** Accessing ECS01

    Figure 6 Accessing ECS01

    Note

    ELB01/ indicates that the default directory named ECS01 is accessed, while ELB01 indicates the file name. Therefore, the slash (/) following ELB01 must be retained.

  4. Use your browser to access http://www.example.com/ELB02/. If the following page is displayed, the load balancer has routed the request to ECS02.

    **Figure 7** Accessing ECS02

    Figure 7 Accessing ECS02

last updated: 2024-05-03 00:42