Using ELB to Distribute Traffic to a Web Application Across ECSs

Scenarios

ELB distributes traffic across ECSs, which eliminates single points of failure (SPOFs) and makes your application more available.

If you have a web application that needs to handle heavy traffic, you can deploy your application on two ECSs (ECS01 and ECS02 in this example) and create a load balancer to distribute traffic across these ECSs.

Figure 1 Using ELB to distribute traffic to an application

Procedure

You can follow the process in Figure 2 to use a load balancer to distribute traffic to a web application.

Figure 2 Distributing traffic to a web application deployed in multiple ECSs

Procedure	What to Do
Step 1: Create a VPC and Two ECSs	Create a VPC with an IPv4 CIDR block and create a subnet in the VPC. VPC IPv4 CIDR block: 192.168.0.0/16 Subnet IPv4 CIDR block: 192.168.0.0/24 Buy two ECSs in the VPC subnet you have created.
Step 2: Deploy the Application	Deploy Nginx on the two ECSs.
Step 3: Create a Load Balancer	Create a load balancer with elastic specifications to receive requests from clients and distribute the requests to backend servers.
Step 4: Configure Security Group Rules	Configure security group rules to allow traffic from the backend subnet where the load balancer works to the backend servers.
Step 5: Add a Listener	Add a listener to the load balancer to check requests from clients and route requests to backend servers in the backend server group.
Step 6: Verify Load Balancing	Access the domain name of the load balancer to check whether different backend servers can be accessed.

Step 1: Create a VPC and Two ECSs

You need to plan the region for your load balancer, and create a VPC and two ECSs. Ensure that the ECSs and load balancer are in the same AZ and VPC.

Create a VPC.

Configuring a VPC

Parameter	Example Value	Description
Name	vpc-A	The VPC name. Set it to vpc-A.
IPv4 CIDR Block	192.168.0.0/16	The IPv4 CIDR block of vpc-A.
Enterprise Project	default	The enterprise project by which VPCs are centrally managed. Select an existing enterprise project for vpc-A.
Advanced Settings (Optional)	N/A	In this example, retain the default value.

Configuring a VPC subnet

Parameter	Example Value	Description
Subnet Name	subnet-elb	The subnet name. Set it to subnet-elb.
IPv4 CIDR Block	192.168.0.0/24	The IPv4 CIDR block of subnet-elb, which is a unique CIDR block with a range of IP addresses in vpc-A.
IPv6 CIDR Block (Optional)	Do not enable	Whether to assign IPv6 addresses.
Associated Route Table	Default	The default route table that subnet-elb is associated with. The default route table has a preset system route that allows subnets in a VPC to communicate with each other.
Advanced Settings (Optional)	N/A	In this example, retain the default value.

Create two ECSs.

Configuring the network parameters for the two ECSs

Parameter	Example Value	Description
ECS Name	ECS01 ECS02	Names of the two ECSs. Set them to ECS01 and ECS02.
Network	vpc-A subnet-elb	The VPC subnet where the ECSs work. Select vpc-A and subnet-elb for the two ECSs.
EIP	EIP01 EIP02	The EIP bound to each ECS for Internet access.

Step 2: Deploy 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.

Log in to the ECSs.
Install and start Nginx.
CentOS 7.6 is used as an example here.
1. Run the wget command to download the Nginx installation package for your operating system in use.
  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 3 Nginx installed successfully

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.

Run the following command to open the index.html file:
```
vim /usr/share/nginx/html/index.html
```
Press i to enter editing mode.

Modify the index.html file.

Modify the following content:

 ...
    <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>

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

Modify the HTML page of ECS02 by referring to step 3 to identify the access to ECS02.

Modifying the HTML Page of ECS02

Run the following command to open the index.html file:
```
vim /usr/share/nginx/html/index.html
```
Press i to enter editing mode.

Modify the index.html file.

Modify the following content:

 ...
    <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>

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

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 4 Nginx successfully deployed on ECS01
- HTML page of ECS02
  Figure 5 Nginx successfully deployed on ECS02

Step 3: Create 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.

In the upper left corner of the page, click and select the desired region.
Select the same region as the two ECSs.
Click in the upper left corner to display Service List and choose Network > Elastic Load Balance.
On the Load Balancers page, click Create Elastic Load Balancer.

On the displayed page, set the parameters as required.

Configuring the basic information

Parameter	Example Value	Description
Type	Dedicated load balancer	Specifies the type of the load balancer. Select Dedicated load balancer. A dedicated load balancer uses dedicated resources. Its performance is not affected by other load balancers.
Region	-	Specifies the desired region. Resources in different regions cannot communicate with each other over internal networks. Select the same region as the ECSs.
AZ	AZ1 AZ2	Specifies the AZ of the load balancer. Select multiple AZs if you need DR capability. The load balancer performance multiplies as the number of AZs increases.
Name	elb-test	Specifies the name of the load balancer.
Enterprise Project	default	Specifies an enterprise project by which cloud resources and members are centrally managed.

Set Specifications to Elastic.

Configure the network parameters and EIP information.

Configuring network parameters

Parameter	Example Value	Description
Network Type	Private IPv4 network	Specifies the network where the load balancer works. In this example, select Private IPv4 network. The load balancer uses the private IPv4 address to process private network requests. To let the load balancer route requests over the Internet, bind an EIP to it.
VPC	N/A	Specifies the VPC where the load balancer works. In this example, select vpc-A.
Frontend Subnet	N/A	Specifies the frontend subnet from which an IPv4 address will be assigned to the load balancer to receive client requests. If IPv6 is enabled, an IPv6 address will also be assigned to the load balancer.
IPv4 Address	Automatically assign IP address	Specifies how you want the IPv4 address to be assigned.
Backend Subnet	Subnet of the load balancer	Specifies the backend subnet from which an IP address will be assigned to the load balancer to forward requests to backend servers.
IP as a Backend	N/A	Specifies whether to add IP addresses as backend servers that are not in the VPC of the load balancer. In this example, leave this feature disabled.
Elastic IPs
EIP	New EIP	Specifies the public IP address that will be bound to the load balancer for receiving and forwarding requests over the Internet. This parameter is mandatory when Network Type is set to IPv4 public network.
EIP Type	Dynamic BGP	Specifies the link type (BGP) when a new EIP is used.
Billed By	Traffic	Specifies how the bandwidth will be billed. In this example, select Traffic. You need to specify a maximum bandwidth and pay for the outbound traffic you use.
Bandwidth (Mbit/s)	100	Specifies the maximum bandwidth when a new EIP is used, in Mbit/s. The value ranges from 1 Mbit/s to 300 Mbit/s.

Specifies the maximum bandwidth. Click to expand the advanced settings and add a description and tags to the load balancer.
Click Create Now.
Confirm the configuration and submit your request.
View the newly created load balancer in the load balancer list.

Step 4: Configure Security Group Rules

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

The security groups configured for backend servers must have inbound rules to allow health check and service traffic from backend subnet of the load balancer to backend servers. By default, the backend subnet of a load balancer is the same as the subnet where the load balancer works.
Network ACL rules are optional for subnets. If network ACL rules are configured for the subnet where backend servers are running, the inbound rules must allow traffic from the backend subnet of the load balancer to the subnet of backend servers.

For details about how to configure security group and network ACL rules, see Security Group and Network ACL RulesSecurity Group and Network ACL Rules.

You can configure security group rules based on Table 1.

Table 1 Security group rules
Direction	Action	Type	Protocol & Port	Source/Destination	Description
Inbound	Allow	IPv4	TCP: 80	Source: 192.168.0.0/24	Allows outbound traffic to ECSs in the security group.
Outbound	Allow	IPv4	All	Destination: 0.0.0.0/0	Allows the ECSs in the security group to access the Internet.

Step 5: Add 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 this backend server group. If a backend server is detected unhealthy, the load balancer will stop routing traffic to it until the backend server recovers.

On the load balancer list page, locate load balancer elb-test and click its name.

On the Listeners tab, click Add Listener and configure parameters based on Table 2.

Table 2 Parameters for configuring a listener
Parameter	Example Value	Description
Name	listener	Specifies the listener name.
Frontend Protocol	HTTP	Specifies the protocol that will be used by the load balancer to receive requests from clients.
Frontend Port	80	Specifies the port that will be used by the load balancer to receive requests from clients.
Redirect	N/A	Specifies whether to redirect requests from the HTTP listener to an HTTPS listener. Disable it in this example.
Access Control	All IP addresses	Specifies how access to the listener is controlled.
Transfer Client IP Address	N/A	Specifies whether to transmit IP addresses of the clients to backend servers. This feature is enabled for dedicated load balancers by default and cannot be disabled.
Advanced Forwarding	N/A	Specifies whether to enable the advanced forwarding policy. Once it is enabled, more forwarding rules and actions are supported. Enable it in this example.

Retain the default values for Advanced Settings. Click Next: Configure Request Routing Policy. On the Configure Routing Policy page, select Create new for Backend Server Group.
Set Load Balancing Algorithm to Weighted round robin and retain the default values for other parameters.
Click Next: Add Backend Server.
- Backend servers: Click Add Backend Server and select ECS01 and ECS02 from the server list.
- Backend ports: Set them to 80. ECS01 and ECS02 will use this port to communicate with the load balancer.
Configure health check parameters. In this example, retain the default settings.
Click Next: Confirm, confirm the settings, and click Submit.

Step 6: Verify Load Balancing

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

Modify the C:\Windows\System32\drivers\etc\hosts file on your PC to map the domain name to the EIP bound to the load balancer.
View the EIP on the Summary page of the load balancer.
Figure 6 hosts file on your PC
Choose Start and enter cmd to open the CLI.
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.
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 7 Accessing ECS01
Use your browser to access http://www.example.com again.
If the following page is displayed, the load balancer has routed the request to ECS02.
Figure 8 Accessing ECS02

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