Overview

Security Groups

A security group is a collection of access control rules for cloud resources, such as cloud servers, containers, and databases, that have the same security protection requirements and that are mutually trusted. After a security group is created, you can configure access rules that will apply to all cloud resources added to this security group.

When you create a FlexusL instance, the system automatically creates a default security group (sg-default-smb) and associates it with the instance. You can also create a security group based on service requirements and associate it with the instance. An instance can be associated with multiple security groups, and traffic to and from the instance is matched by priority in a descending order.

Each security group can have both inbound and outbound rules. You need to specify the source, port, and protocol for each inbound rule and specify the destination, port, and protocol for each outbound rule to control the inbound and outbound traffic to and from the instances in the security group. Figure 1 shows an example of a security group architecture. In region A, after a FlexusL instance is created, it is automatically associated with the default VPC vpc-default-smb and subnet subnet-default-smb. The FlexusL instance is also associated with the default security group sg-default-smb in subnet-default-smb to ensure the network safety for the FlexusL instance.

Security group sg-default-smb has a custom inbound rule to allow ICMP traffic to the FlexusL instance from your PC over all ports. However, the security group does not contain a rule to allow external access to the instance over the SSH port 22 or RDP port 3389. As a result, you cannot remotely log in to the FlexusL instance from your PC.
If the FlexusL instance needs to access the Internet through an EIP, the outbound rule of sg-default-smb must allow all traffic from the FlexusL instance to the Internet.

Figure 1 A security group architecture

For more information about security groups, see Security Group.

Security Group Rules

A security group has inbound and outbound rules to control traffic that is allowed to reach or leave the instances associated with the security group.

Inbound rules: control traffic to the instances in a security group.
Outbound rules: control traffic from the instances in a security group to access external networks.

You can specify a protocol, port, source or destination for a security group rule. The following describes key information about a security group.

**Table 1** Key parameters of a security group rule
Parameter	Description
Priority	The value ranges from 1 to 100. A smaller value indicates a higher priority. Security group rules are matched by priority and then by action. Deny rules take precedence over allow rules.
Action	Allow or Deny. If the protocol, port, source or destination of the traffic matches a security group rule, traffic will be allowed or denied.
Type	IPv4 or IPv6.
Protocol & Port	Network protocol type and port range. Network protocol: the protocol that is used to match traffic. The protocol can be TCP, UDP, ICMP, or GRE. Port range: the destination port that is used to match traffic. The value ranges from 1 to 65535.
Source or Destination	Source address of traffic in the inbound direction or destination address of traffic in the outbound direction. The source or destination can be an IP address, security group, or IP address group. IP address: a fixed IPv4/IPv6 address or IPv4/IPv6 CIDR block, for example, 192.168.10.10/32 (IPv4 address), 192.168.1.0/24 (IPv4 CIDR block), or 2407:c080:802:469::/64 (IPv6 CIDR block). Security group: If the selected security group and the current security group are in the same region, the traffic is allowed or denied to the private IP addresses of all instances in the selected security group. For example, if there is instance A in security group A and instance B in security group B, and the inbound rule of security group A allows traffic from security group B, traffic is allowed from instance B to instance A. IP address group: If you have multiple IP addresses with the same security requirements, you can add them to an IP address group and select this IP address group when you configure a rule, to help you manage them in an easier way.

By default, the inbound rules of FlexusL default security group sg-default-smb only allow instances in the same security group to communicate with each other and deny all external requests. The security group outbound rules enable all ports and allow all requests that originate from the instances in the security group. Each security group has default rules. For details, see Table 2. You can also customize security group rules. For details, see Configuring Security Group Rules for a FlexusL Instance.

**Table 2** Default security group rules
Direction	Action	Type	Protocol & Port	Source/Destination	Description
Inbound	Allow	IPv4	All	Source: sg-default-smb	Allows instances in the security group to communicate with each other over IPv4 protocols.
Inbound	Allow	IPv6	All	Source: sg-default-smb	Allows instances in the security group to communicate with each other over IPv6 protocols.
Outbound	Allow	IPv4	All	Destination: 0.0.0.0/0	Allows access from instances in the security group to any IPv4 address over any port.
Outbound	Allow	IPv6	All	Destination: ::/0	Allows access from instances in the security group to any IPv6 address over any port.

If the source is set to 0.0.0.0/0 or::/0, 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 source in security group rules.

Security Group Constraints

By default, you can create up to 100 security groups in your cloud account.
By default, you can add up to 50 rules to a security group.
For better network performance, you are advised to associate no more than five security groups with a FlexusL instance or supplementary network interface.
You can add up to 20 instances to a security group at a time.
You can add up to 1,000 instances to a security group.