Security groups are configured to manage whether a Cloud Virtual Machine (CVM) can be accessed. You can configure inbound and outbound rules for security groups to specify whether your server can be accessed or can access other network resources.
Default inbound and outbound rules for security groups are as follows:

• To ensure data security, the inbound rule for a security group is a rejection policy that denies remote access from external networks. To allow your CVM to be accessed externally, you need to open the inbound rule for the corresponding port to the Internet.
• The outbound rule for a security group specifies whether your CVM can access external network resources. If you select Open All Ports or Open Ports 22, 80, 443, and 3389 and ICMP, the outbound rule for the security group opens all ports to the Internet. If you select a custom security group rule, the outbound rule blocks all ports by default, and you need to set the outbound rule to allow the corresponding port to access external network resources.

Common Use Cases

This document introduces several common use cases for security groups. If any of the following cases meets your requirements, you can set your security groups according to the configuration recommended for the corresponding use case.

Scenario 1: Remotely Connecting to a Linux CVM via SSH

Case: You have created a Linux CVM and want to remotely connect to the CVM via SSH.
Solution: When Adding an Inbound Rule, set Type to Linux login and open TCP port 22 to the Internet to allow Linux login via SSH.
You can open all IP addresses or a specified IP address (or IP address range) to the Internet as required. This allows you to configure the source IP addresses of the CVMs that can be remotely connected to via SSH.

Scenario 2: Remotely Connecting to a Windows CVM via RDP

Case: You have created a Windows CVM and want to remotely connect to the CVM via Remote Desktop Connection (RDP).
Solution: When Adding an Inbound Rule, set Type to Windows login and open TCP port 3389 to the Internet to enable remote login to Windows.
You can open all IP addresses or a specified IP address (or IP address range) to the Internet as required. This enables you to configure the source IP addresses of the CVMs that can be remotely connected to via RDP.

Scenario 3: Pinging a CVM on a Public Network

Case: You have created a CVM and want to test whether the communication between this CVM and other CVMs is normal.
Solution: Test the connection by using the ping program. Specifically, when Adding an Inbound Rule, set Type to Ping and open Internet Control Message Protocol (ICMP) ports to the Internet to enable other CVMs to gain access to this CVM by using ICMP.
You can open all IP addresses or a specified IP address (or IP address range) to the Internet as required. This allows you to configure the source IP addresses of the CVMs that can gain access to this CVM by using ICMP.

Scenario 4: Remotely Logging In to a CVM via Telnet

Case: You want to remotely log in to a CVM via Telnet.
Solution: When Adding an Inbound Rule, configure the following security group rule:

Scenario 5: Authorizing Access to a Web Service via HTTP or HTTPS

Case: You have built a website and want to allow users to access your website via HTTP or HTTPS.
Solution: When Adding an Inbound Rule, configure the following security group rules as required:

• Allow all IP addresses on the public network to access this website

  Direction	Type	Source	Protocol and Port	Policy
  Inbound	HTTP (80)	0.0.0.0/0	TCP: 80	Allow
  Inbound	HTTPS (443)	0.0.0.0/0	TCP: 443	Allow

• Allow some IP addresses on the public network to access this website.

  Direction	Type	Source	Protocol and Port	Policy
  Inbound	HTTP (80)	The IP address or IP address range that is allowed to access your website	TCP: 80	Allow
  Inbound	HTTPS (443)	The IP address or IP address range that is allowed to access your website	TCP: 443	Allow

Scenario 6: Allowing an External IP Address to Access a Specified Port

Case: You have deployed a service and want the specified service port (such as port 1101) to be externally accessible.
Solution: When Adding an Inbound Rule, set Type to Custom and open TCP port 1101 to the Internet to allow external access to the specified service port.
You can open all IP addresses or a specified IP address (or IP address range) to the Internet as required. This allows the source IP address to access the specified service port.

Scenario 7: Denying Access to a Specified Port from External IP Addresses

Case: You have deployed a service and want to prevent external access to a specified service port (such as port 1102).
Solution: When Adding an Inbound Rule, set Type to Custom, configure TCP port 1102, and set Policy to Reject to deny external access to the specified service port.

Scenario 8: Allowing a CVM to Access Only a Specified External IP Address

Case: You want your CVM to access only a specified external IP address.
Solution: Add two outbound security group rules by referring to the following configurations:

• Allow the CVM instance to access a specified external IP address
• Disallow the CVM instance to access any public IP addresses via any protocol.

Rules that permit access have a higher priority than those that deny access.

Scenario 9: Denying a CVM from Accessing a Specified External IP Address

Case: You do not want your CVM to access a specified external IP address.
-Solution: Add a security group rule by referring to the following configuration:

Scenario 10: Uploading or Downloading a File to or from a CVM via FTP

Case: You want to upload a file to or download a file from a CVM by using an FTP program.
-Solution: Add a security group rule by referring to the following configuration:

Combination of Multiple Scenarios

In an actual scenario, you may want to configure multiple security group rules based on service requirements; for example, configuring inbound or outbound rules at the same time. One CVM may be bound to one or more security groups. When a CVM is bound to multiple security groups, these security groups are matched and executed in descending order of priorities. You can adjust the priorities of these security groups whenever needed. For more information about the priorities of security group rules, see Rule Priorities.