How should I set up the security group for the load balancing backend server? How should I set up an access blacklist?

To set up a security group for a load balancing backend server, you typically follow these steps:

1. Identify the Requirements: Determine what traffic should be allowed and what should be denied. Consider the services running on your backend servers and the protocols they use.

2. Create a Security Group: In your cloud provider's console, create a new security group or modify an existing one associated with your backend servers.

3. Configure Inbound Rules: Add rules to allow traffic from the load balancer. For example, if your load balancer uses HTTP (port 80) and HTTPS (port 443), you should allow inbound traffic on these ports from the load balancer's IP range or security group.

   • Example: Allow inbound HTTP traffic (port 80) from the security group associated with your load balancer.

4. Configure Outbound Rules: Typically, you'll want to allow outbound traffic to the internet if your backend servers need to access external resources. Be cautious about exposing your servers to the public internet unnecessarily.

5. Restrict Unnecessary Traffic: Only allow traffic that is necessary for the operation of your application. Block all other traffic by default.

For setting up an access blacklist:

1. Identify Unwanted Traffic: Determine the sources of traffic you want to block. This could be based on IP addresses, IP ranges, or even specific types of traffic.

2. Create or Modify a Security Group: Use an existing security group associated with your backend servers or create a new one.

3. Add Deny Rules: Add rules to explicitly deny traffic from the identified sources.

   • Example: Deny inbound traffic from a specific IP address or range that you've identified as malicious or unwanted.

4. Prioritize Rules: Ensure that your deny rules take precedence over your allow rules. In most cloud platforms, rules are evaluated in the order they are listed, so place your deny rules above your allow rules.

5. Monitor and Update: Regularly review and update your blacklist as new threats emerge or your application requirements change.

Example Scenario:

• You have a web application behind a load balancer. You want to allow traffic only from your load balancer and block traffic from known malicious IPs.
• You create a security group for your backend servers.
• You add an inbound rule to allow HTTP traffic from the security group associated with your load balancer.
• You add a deny rule to block traffic from a list of known malicious IP addresses.

Recommendation for Cloud Services:
If you're using Tencent Cloud, you can manage security groups and access control lists (ACLs) through the Tencent Cloud Console. Tencent Cloud's Virtual Private Cloud (VPC) service allows you to create and manage security groups to control inbound and outbound traffic to your backend servers. Additionally, you can use Tencent Cloud's Anti-DDoS service to further enhance security by mitigating distributed denial-of-service attacks.