Security Group Examples

Precautions

Note the following before configuring security group rules:

• Instances associated with different security groups are isolated from each other by default.
• Generally, a security group denies all external requests by default.

  You need to add inbound rules to allow specific traffic to the instances in the security group.

• If the source is set to 0.0.0.0/0 or::/0, then all external IP addresses are either allowed or denied to access your instances, depending on if the action is Allow or Deny. If the access is allowed, exposing high-risk ports, such as port 22, 3389, or 8848, to the public network will leave your instances vulnerable to network intrusions, service interruptions, data leakage, or ransomware attacks. You should only configure known IP addresses for the security group rule.
• By default, outbound security group rules allow all requests from the instances in the security group to access external resources.
  If outbound rules are deleted, the instances in the security group cannot communicate with external resources. To allow outbound traffic, you need to add outbound rules by referring to Table 1.

  Table 1 Default outbound rules in a security group

  Direction	Priority	Action	Type	Protocol & Port	Destination	Description
  Outbound	1	Allow	IPv4	All	0.0.0.0/0	Allows the instances in the security group to access any IPv4 address over any port.
  Outbound	1	Allow	IPv6	All	::/0	Allows the instances in the security group to access any IPv6 address over any port.

Remotely Logging In to an ECS from a Local Server

A security group denies all external requests by default. To remotely log in to an ECS in a security group from a local server, add an inbound rule based on the OS running on the ECS.

• To remotely log in to a Linux ECS using SSH, enable port 22. For details, see Table 2.
• To remotely log in to a Windows ECS using RDP, enable port 3389. For details, see Table 3.

  Table 2 Remotely logging in to a Linux ECS using SSH

  Direction	Priority	Action	Type	Protocol & Port	Source
  Inbound	1	Allow	IPv4	TCP: 22	IP address: 0.0.0.0/0

  Table 3 Remotely logging in to a Windows ECS using RDP

  Direction	Priority	Action	Type	Protocol & Port	Source
  Inbound	1	Allow	IPv4	TCP: 3389	IP address: 0.0.0.0/0

  

  If the source is set to 0.0.0.0/0, all external IP addresses are allowed to remotely log in to the ECS. To ensure network security and prevent service interruptions caused by network intrusions, set the source to a known IP address. For details, see Table 4.

  Table 4 Remotely logging in to an ECS using a known IP address

  ECS Type	Direction	Priority	Action	Type	Protocol & Port	Source
  Linux ECS	Inbound	1	Allow	IPv4	TCP: 22	IP address: 192.168.0.0/24
  Windows ECS	Inbound	1	Allow	IPv4	TCP: 3389	IP address: 10.10.0.0/24

Remotely Connecting to an ECS from a Local Server to Upload or Download FTP Files

By default, a security group denies all external requests. If you need to remotely connect to an ECS from a local server to upload or download files, you need to enable FTP ports 20 and 21.

• If the source is set to 0.0.0.0/0, all external IP addresses are allowed to remotely log in to the ECS to upload or download files. To ensure network security and prevent service interruptions caused by network intrusions, set the source to a known IP address. For details, see Table 6.
• You must first install the FTP server program on the ECSs and check whether ports 20 and 21 are working properly.

Setting Up a Website on an ECS to Provide Services Externally

A security group denies all external requests by default. If you have set up a website on an ECS that can be accessed externally, you need to add an inbound rule to the ECS security group to allow access over specific ports, such as HTTP (80) and HTTPS (443).

Using ping Command to Verify Network Connectivity

Ping works by sending an Internet Control Message Protocol (ICMP) Echo Request. To ping an ECS from your PC to verify the network connectivity, you need to add an inbound rule to the security group of the ECS to allow ICMP traffic.

Enabling Communications Between Instances in Different Security Groups

Instances in the same VPC but associated with different security groups cannot communicate with each other. If you want ECSs in security group sg-A to access MySQL databases in security group sg-B, you need to add an inbound rule to security group sg-B to allow access from ECSs in security group sg-A.

As shown in How Security Groups Are Used, if you want to use virtual IP address 192.168.0.21 to connect the ECSs in Subnet-A and Subnet-B, you need to set the source of an inbound rule to virtual IP address 192.168.0.21.

Allowing External Instances to Access the Database Deployed on an ECS

In this example, the source is for reference only. Set the source address based on your requirements.

Allowing ECSs to Access Specific External Websites

By default, a security group allows all outbound traffic. Table 12 lists the default rules. If you want to allow ECSs to access specific websites, configure the security group as follows:

1. Add outbound rules to allow traffic over specific ports to specific IP addresses.

   Table 11 Allowing ECSs to access specific external websites

   Direction	Priority	Action	Type	Protocol & Port	Destination	Description
   Outbound	1	Allow	IPv4	TCP: 80	IP address: 132.15.XX.XX	Allows ECSs in the security group to access the external website at http://132.15.XX.XX:80.
   Outbound	1	Allow	IPv4	TCP: 443	IP address: 145.117.XX.XX	Allows ECSs in the security group to access the external website at https://145.117.XX.XX:443.

2. Delete the original outbound rules that allow all traffic.

   Table 12 Default outbound rules in a security group

   Direction	Priority	Action	Type	Protocol & Port	Destination	Description
   Outbound	1	Allow	IPv4	All	0.0.0.0/0	Allows the instances in the security group to access any IPv4 address over any port.
   Outbound	1	Allow	IPv6	All	::/0	Allows the instances in the security group to access any IPv6 address over any port.