Configure access control based on listeners and ports by using security groups - Server Load Balancer

To regulate access from requests, you can configure a security group to implement access control based on protocols, ports, and IP addresses. Security groups provide finer-grained access control than access control lists. Security groups not only support access control based on protocols and ports, but also support access control policies that regulate access from IPv6 addresses.

Scenario

Before the ALB instance is added to a security group, the listener ports of the ALB instance allow all requests by default.
After the ALB instance is added to a security group which does not contain Deny rules, the listener ports of the ALB instance allow all requests by default. If you want to allow requests only from specific IP addresses to your ALB instance, you must also create a Deny rule.

If you want to control inbound access to your Application Load Balancer (ALB) instance, you can add the ALB instance to a security group and configure security group rules based on your security requirements.

Important

Outbound traffic of ALB refers to response packets that are returned to users. To maintain service availability, security groups do not block outbound traffic of ALB. You do not need to configure security group rules to allow outbound traffic.

If you want to block access to some listener ports but allow access to other listener ports, you can configure the security group to control access to the ports. The following table describes how to enable access control on ports for the ALB instance by configuring a security group in three different scenarios. In the scenarios, an HTTP listener that listens on port 80 and an HTTP listener that listens on port 81 are configured for the ALB instance.

Scenario	Security group rule	Expected result	References
Before the ALB instance is added to a security group	By default, the listener ports of the ALB instance allow all requests.	Clients can access the HTTP port 80 of the ALB instance Clients can access the HTTP port 81 of the ALB instance	Step 5: Test network connectivity before the ALB instance is added to the security group
Add the ALB instance to a security group	Block requests to HTTP port 81 Note This section describes only the security group rules that are relevant to this topic. Other default rules are not described.	Clients can access the HTTP port 80 of the ALB instance Clients cannot access the HTTP port 81 of the ALB instance	Step 6: Add the ALB instance to a security group and verify the result
Modify the security group rules	Block requests to the HTTP port 80 Block requests to the HTTP port 81 Note This section describes only the security group rules that are relevant to this topic. Other default rules are not described.	Clients cannot access the HTTP port 80 of the ALB instance Clients cannot access the HTTP port 81 of the ALB instance	Step 7: Modify the security group rules and verify the result

Limits

By default, security groups are unavailable. To use security groups, contact your account manager.

Category	Security group type	Description
Security groups supported by ALB	Basic security group Advanced security group	The security group must be in a virtual private cloud (VPC), and the security group and ALB instance must be in the same VPC. Each ALB instance can be added to at most four security groups and supports at most 800 security group rules. The security groups of the same ALB instance must be of the same type. For example, an ALB instance can be added to multiple basic security groups or multiple advanced security groups. To add an ALB instance that is already in a basic security group to an advanced security group, you must first remove the ALB instance from the basic security group. The same rule applies if you want to add an ALB instance that is already in an advanced security group to a basic security group.
Security groups not supported by ALB	Managed security group	For more information about managed security groups, see Managed security groups.

Prerequisites

A virtual private cloud (VPC) named VPC1 is created. For more information, see Create and manage a VPC.
Two Elastic Compute Service (ECS) instances named ECS01 and ECS02 are created in VPC1. ECS01 and ECS02 function as backend servers of the ALB instance. Different applications are deployed on ECS01 and ECS02.
- For more information about how to create an ECS instance, see Create an instance by using the wizard.
- The following sample code show how to deploy test applications on ECS01 and ECS 02.
  Commands for deploying an application on ECS01
```
yum install -y nginx
systemctl start nginx.service
cd /usr/share/nginx/html/
echo "Hello World !  This is ECS01." > index.html
```
  Commands for deploying an application on ECS02
```
yum install -y nginx
systemctl start nginx.service
cd /usr/share/nginx/html/
echo "Hello World !  This is ECS02." > index.html
```

A domain name is registered, and an Internet content provider (ICP) number is obtained for the domain name. For more information, see Register a domain name on Alibaba Cloud and Overview.

Procedure

Step 1: Create a server group for the ALB instance

Log on to the ALB console.
In the top navigation bar, select the region in which you want to create a server group. In this example, China (Hangzhou) is selected.
In the left-side navigation pane, choose ALB > Server Groups.
On the Server Groups page, click Create Server Group.

In the Create Server Group dialog box, configure the parameters and click Create.

The following table describes the parameters that are relevant to this topic. Use the default values for the other parameters. For more information, see Create and manage server groups.

Parameter	Description
Server Group Type	Select a type of server group. In this example, Server is selected.
Server Group Name	Enter a name for the server group.
VPC	Select the VPC in which you want to create the server group. In this example, VPC1 is selected.
Backend Server Protocol	Select a backend protocol. In this example, HTTP is selected.
Scheduling Algorithm	Select a scheduling algorithm. In this example, Weighted Round-robin is selected.

In the The server group is created dialog box, click Add Backend Server.
On the Backend Servers tab, click Add Backend Server.
In the Add Backend Server panel, select ECS01 and ECS02 and click Next.
Specify ports and weights for the backend servers and click OK.

Step 2: Create an ALB instance and configure listeners

Log on to the ALB console.
On the Instances page, click Create ALB.
On the buy page, configure the following parameters.
The following table describes only some of the parameters. Keep the default values for other parameters. For more information, see Create an ALB instance.
- Region: the region in which you want to create the ALB instance. In this example, China (Hangzhou) is selected.
- Network Type: the network type of the ALB instance. In this example, Internet is selected.
- VPC: the VPC in which you want to create the ALB instance. In this example, VPC1 is selected.
Click Buy Now and complete the payment.
Return to the Instances page and click the ID of the ALB instance.
Click the Listener tab and then click Quick Create Listener.

In the Quick Create Listener dialog box, configure the parameters and click OK. In this example, an HTTP listener that listens on port 80 is created. The following table describes the parameters.

Parameter	Description
Listener Protocol	Select a listener protocol. In this example, HTTP is selected.
Listener Port	Enter a listener port. In this example, port 80 is specified.
Server Group	Select Server Type and select a server group from the drop-down list next to Server Type. In this example, the server group created in Step 1 is selected.

On the Listener tab, click Quick Create Listener.

In the Quick Create Listener dialog box, configure the parameters and click OK. In this example, an HTTP listener that listens on port 81 is created. The following table describes the parameters.

Parameter	Description
Listener Protocol	Select a listener protocol. In this example, HTTP is selected.
Listener Port	Enter a listener port. In this example, port 81 is specified.
Server Group	Select Server Type and select a server group from the drop-down list next to Server Type. In this example, the server group created in Step 1 is selected.

Step 3: Configure a CNAME record

Copy the domain name of the ALB instance and perform the following operations to add a CNAME record that maps your custom domain name to the domain name of the ALB instance.

Log on to the Alibaba Cloud DNS console.
On the Domain Name Resolution page, click Add Domain Name.
In the Add Domain Name dialog box, enter the domain name of your host and click OK.
Important
Before you create a CNAME record, you must use a TXT record to verify the ownership of the domain name.
Find the domain names that you want to manage and click DNS Settings in the Actions column.
On the DNS Settings page, click Add DNS Record.

In the Add DNS Record panel, set the following parameters and click OK.

Parameter	Description
Record Type	Select CNAME from the drop-down list.
Hostname	Enter the prefix of the domain name of your host.
DNS Request Source	Select Default.
Record Value	Enter the CNAME, which is the domain name of the ALB instance.
TTL	Select a time-to-live (TTL) value for the CNAME record to be cached on the DNS server. In this example, the default value is used.

Step 4: Create a security group

Before you can add the ALB instance to a security group, you need to create a security group in the ECS console.

Log on to the ECS console.
In the left-side navigation pane, choose Network & Security > Security Groups.
In the top navigation bar, select the region in which you want to create a security group. In this example, China (Hangzhou) is selected.
On the Security Groups page, click Create Security Group.
On the Create Security Group page, configure the parameters in the Basic Information section.
The following section describes only the parameters that are relevant to this topic. For more information about other parameters, see Create a security group.
- Quick Create Listener: In this example, VPC1 is selected.
- Security Group Type: In this example, Basic Security Group is selected.

Add an access rule to the security group.

On the Inbound tab, click Add Rule.

Configure the parameters and click Create Security Group. The following table describes the parameters.

Parameter	Description
Action	Select Deny.
Priority	The default value 1 is used.
Protocol Type	Select Custom TCP. Note To add a security group rule for a QUIC listener, select Custom UDP.
Port Range	Enter the port number `81`.
Authorization Object	Select `All IPv4 Addresses (0.0.0.0/0)` and `All IPv6 Addresses ((::/0)`.
Description	Enter a description for the security group rule.

Step 5: Test the network connectivity before the ALB instance is added to the security group

Test the network connectivity between a client and ECS01 and ECS02. In this example, a client that has Internet access is used.

Enter the domain name and port number into the address bar of the browser, such as http://Domain name:80 and press Enter. The following figure shows that the ALB instance can access the HTTP port 80.
Enter the domain name and port number into the address bar of the browser, such as http://Domain name:81 and press Enter. The following figure shows that the ALB instance can access the HTTP port 81.

Step 6: Add the ALB instance to the security group and verify the result

Add the ALB instance to the security group and test whether the security group rule takes effect on the ports.

Log on to the ALB console.
On the Instances page, click the ID of the ALB instance that you want to manage. On the Instance Details tab, click the Security Groups tab.
On the Security Groups tab, click Create Security Group. In the Add ALB Instance to Security Group dialog box, select the security group created in Step 4: Create a security group, and click OK.

In the left-side panel, click the ID of the security group that you want to manage. You can click the Inbound Policies or Outbound Policies tab to view the security group rules.

The following table describes only the inbound rules that are relevant to this topic. The ALB instance uses the following security group rules.

Policy	Priority	Protocol Type	Port Range	Authorization Object
Allow	1	Custom TCP	`Destination: 80/80`	`Source: All IPv4 Addresses (0.0.0.0/0)`
Allow	1	Custom TCP	`Destination: 80/80`	`Source: All IPv6 Addresses (::/0)`
Deny	1	Custom TCP	`Destination: 81/81`	`Source: All IPv4 Addresses (0.0.0.0/0)`
Deny	1	Custom TCP	`Destination: 81/81`	`Source: All IPv6 Addresses (::/0)`

Modify the security groups and verify the result.
1. Enter the domain name and port number into the address bar of the browser, such as http://Domain name:80 and press Enter. The following figure shows that the ALB instance can access the HTTP port 80.
2. Enter the domain name and port number into the address bar of the browser, such as http://Domain name:81 and press Enter. If you cannot access the application, open the command-line interface (CLI) and run the following command: curl http://Domain name:81. The following figure shows that the client cannot access the HTTP port 81 on the ALB instance. This result indicates that the security group rules take effect on port 81.

Step 7: Modify the security group rules and verify the result

Modify the security group rules and test whether the security group rules can take effect on the ports.

Return to the Instances page and click the ID of the ALB instance. On the Instance Details tab, click the Security Groups tab.
In the Basic Information section, click the ID of the security group. You can also click ECS Console in the upper-right corner of the Security Groups tab to go to the Security Group Details page.

On the Security Group Detail page, find the security group rule that allows access to TCP port 80 and click Modify in the Actions column. Set Action to Deny and click Save.

The following table describes only the security group rules that are relevant to this topic. The following table describes the new security group rules.

Policy	Priority	Protocol Type	Port Range	Authorization Object
Deny	1	Custom TCP	`Destination: 80/80`	`Source: All IPv4 Addresses (0.0.0.0/0)`
Deny	1	Custom TCP	`Destination: 80/80`	`Source: All IPv6 Addresses (::/0)`
Deny	1	Custom TCP	`Destination: 81/81`	`Source: All IPv4 Addresses (0.0.0.0/0)`
Deny	1	Custom TCP	`Destination: 81/81`	`Source: All IPv6 Addresses (::/0)`

After you modify the security group rules, test the accessibility of the ports.
1. Open the CLI and run the following command: curl http://Domain name:80. The following figure shows that the client cannot access the HTTP port 80 on the ALB instance. This result indicates that the security group rules take effect on port 80.
2. Open the CLI and run the following command: curl http://Domain name:81. The following figure shows that the client cannot access the HTTP port 81 on the ALB instance. This result indicates that the security group rules take effect on port 81.

References

For more information about how to add an ALB instance to and remove an ALB instance from a security group, see Add an ALB instance to a security group.
For more information about how to configure a whitelist and a blacklist for an ALB instance, see Use security groups as blacklists or whitelists for ALB.
For more information about basic security groups and advanced security groups, see Basic security groups and advanced security groups.
LoadBalancerJoinSecurityGroup: adds an ALB instance to a security group.
LoadBalancerLeaveSecurityGroup: removes an ALB instance from a security group.