11 ‐ Scenario‐Based Questions and Answers for Load Balancer & Firewall in OCI - SanjeevOCI/Study GitHub Wiki

Scenario-Based Questions and Answers for Load Balancer & Firewall in OCI

Load Balancer Scenarios

1. Scenario: Configuring a Load Balancer for High Availability

Question:
You have deployed a web application across two compute instances in different availability domains (ADs). How would you configure an OCI Load Balancer to ensure high availability?

Answer:

  • Deploy an OCI Load Balancer in the same VCN as the compute instances.
  • Add both compute instances to the Backend Set.
  • Configure Health Checks to monitor the availability of the backend instances.
  • Use a Regional Load Balancer to distribute traffic across multiple ADs.
  • Ensure the Load Balancer is in a public subnet if it needs to handle internet traffic.

2. Scenario: Securing Traffic to a Load Balancer

Question:
How would you secure traffic to an OCI Load Balancer to ensure only HTTPS traffic is allowed?

Answer:

  • Configure an SSL Certificate on the Load Balancer for HTTPS traffic.
  • Create a Listener on port 443 for HTTPS.
  • Do not configure a listener for HTTP (port 80) to block non-secure traffic.
  • Use Network Security Groups (NSGs) or Security Lists to allow only port 443 traffic to the Load Balancer.

3. Scenario: Load Balancer for Internal Applications

Question:
You need to set up a Load Balancer for an internal application that should not be accessible from the internet. How would you configure it?

Answer:

  • Deploy a Private Load Balancer in a private subnet within the VCN.
  • Ensure the backend instances are also in private subnets.
  • Use NSGs to restrict access to the Load Balancer from specific IP ranges or subnets.
  • Do not associate a public IP with the Load Balancer.

4. Scenario: Load Balancer Health Check Failing

Question:
Your Load Balancer health check is failing for one of the backend instances. How would you troubleshoot this issue?

Answer:

  • Verify that the backend instance is running and accessible.
  • Check the Health Check Configuration (protocol, port, and path) to ensure it matches the application settings.
  • Ensure the Security List or NSG allows traffic from the Load Balancer's IP range to the backend instance.
  • Check the application logs on the backend instance for errors.

5. Scenario: Load Balancer Scaling

Question:
Your application traffic has increased significantly, and the Load Balancer is struggling to handle the load. How would you scale the Load Balancer?

Answer:

  • Use an OCI Flexible Load Balancer, which automatically scales based on traffic.
  • If using a fixed shape Load Balancer, upgrade to a larger shape (e.g., from 10 Mbps to 100 Mbps).
  • Add more backend instances to the Backend Set to distribute the load.

Firewall Scenarios

1. Scenario: Restricting Access to a Compute Instance

Question:
You need to restrict SSH access to a compute instance to a specific IP address. How would you configure this?

Answer:

  • Use a Network Security Group (NSG) or Security List to allow inbound traffic on port 22 only from the specific IP address.
  • Example NSG Rule:
    • Source CIDR: <specific-IP>/32
    • Protocol: TCP
    • Port Range: 22

2. Scenario: Allowing Internet Access for a Private Subnet

Question:
You have a private subnet, and the instances in it need to access the internet for updates. How would you configure this securely?

Answer:

  • Deploy a NAT Gateway in the VCN.
  • Update the Route Table for the private subnet to route all outbound traffic (0.0.0.0/0) through the NAT Gateway.
  • Ensure the Security List or NSG allows outbound traffic on required ports (e.g., 80, 443).

3. Scenario: Blocking Traffic from a Specific IP Range

Question:
How would you block traffic from a specific IP range to your application hosted in OCI?

Answer:

  • Use a Network Security Group (NSG) or Security List to create a Deny Rule for the specific IP range.
  • Example NSG Rule:
    • Source CIDR: <blocked-IP-range>
    • Action: Deny
    • Protocol: All

4. Scenario: Configuring Stateful vs Stateless Rules

Question:
What is the difference between stateful and stateless rules in OCI Security Lists, and when would you use each?

Answer:

  • Stateful Rules: Automatically allow return traffic for an allowed connection. Use for most scenarios where bidirectional communication is required.
  • Stateless Rules: Require explicit rules for both inbound and outbound traffic. Use for scenarios where fine-grained control is needed, such as load balancers or NAT Gateways.

5. Scenario: Securing Object Storage Access

Question:
You need to allow a compute instance in a private subnet to access an Object Storage bucket securely. How would you configure this?

Answer:

  • Use a Service Gateway to enable private access to Object Storage.
  • Update the Route Table for the private subnet to route traffic to the Service Gateway.
  • Ensure the Security List or NSG allows outbound traffic to the Service Gateway.

Summary

These scenario-based questions and answers cover practical use cases for Load Balancers and Firewalls in OCI, focusing on security, scalability, and troubleshooting.