What are Cloud Firewalls and Network Security Groups, and How Do They Secure Workloads in the Cloud?

Key takeaways

• A cloud firewall filters at the edge or between networks, while a network security group filters at the subnet or interface.
• Open only the ports each workload needs, and prefer allow-lists to broad rules.
• Layer them with network ACLs for defence in depth.

Table of Contents

• Why is securing cloud workloads with firewalls and NSGs critical?
• What is a Cloud Firewall?
• What Are Network Security Groups (NSGs)?
• Why Defense in Depth is Essential
• Securing Cloud Workloads Across Zones (with Real Examples)
• Best Practices for Using NSGs and Firewalls
• Automating Security Policies Using Code
• Conclusion

Why is securing cloud workloads with firewalls and NSGs critical?

As organizations increasingly migrate to cloud platforms like AWS, Azure, and Google Cloud, security remains a top concern. One of the most vital components of cloud security is network segmentation and access control, achieved using Cloud Firewalls and Network Security Groups (NSGs). These tools allow you to build multi-layered security (defense in depth) by filtering traffic at various levels, from the perimeter to individual workloads.

This blog breaks down what cloud firewalls and NSGs are, how they work, and how you can secure your cloud deployments using real-world examples, automation tools, and cloud-native features.

What is a Cloud Firewall?

A Cloud Firewall is a virtual firewall hosted and managed within a cloud provider's infrastructure. It protects your cloud-based workloads by filtering ingress (inbound) and egress (outbound) traffic based on defined security policies.

Key Features:

• Stateful or stateless inspection

• Supports layer 3–7 filtering

• Geo-blocking, DDoS protection, and traffic logging

• Centralized management via APIs or dashboards

Real Example:

In Google Cloud Platform, you can create VPC firewall rules to only allow SSH access to your VM instances from specific IP ranges. This prevents brute-force attacks from the internet.

What Are Network Security Groups (NSGs)?

Network Security Groups are access control lists that filter traffic to and from network interfaces, subnets, or VMs, particularly in Microsoft Azure and AWS Security Groups.

They act as mini-firewalls with default deny-all rules, and only allow the traffic that matches explicit allow rules.

Key Use Cases:

• Allowing web traffic (HTTP/HTTPS) only to web servers

• Denying all traffic except from internal corporate IPs

• Controlling access between tiers (web, app, DB)

Cloud Firewalls vs NSGs vs ACLs – What's the Difference?

Why Defense in Depth is Essential

In traditional networks, firewalls were perimeter-based. But in the cloud, you need layered defense. That includes:

• Cloud Firewalls for perimeter filtering

• NSGs for internal segmentation

• ACLs for fine-grained control

• Web Application Firewalls (WAFs) for HTTP-layer defense

Defense in depth helps prevent lateral movement in case of a breach.

Securing Cloud Workloads Across Zones (with Real Examples)

Example 1: Azure NSG for App Isolation

You have a three-tier app on Azure: Web, App, and DB.

• Web tier NSG: Allow HTTP/HTTPS

• App tier NSG: Allow traffic only from Web tier

• DB tier NSG: Allow only port 1433 from App tier

This segmentation ensures zero trust between layers.

Example 2: AWS Security Groups with ELB

In AWS:

• Attach a Security Group to ELB allowing inbound on 443

• Backend EC2s have SG allowing only traffic from ELB

• Admin SG allows SSH only from your IP

Best Practices for Using NSGs and Firewalls

• Start with deny-all, then allow needed rules

• Apply least privilege: only expose required ports

• Use tags and dynamic groups to simplify policy management

• Enable flow logs to monitor traffic

• Automate security policies with Terraform or Bicep

Automating Security Policies Using Code

Security rules can be deployed via Infrastructure as Code (IaC) tools.

Terraform Example:

resource "azurerm_network_security_group" "example" {
 name = "web-nsg"
 location = azurerm_resource_group.example.location
 resource_group_name = azurerm_resource_group.example.name

 security_rule {
 name = "AllowHTTP"
 priority = 100
 direction = "Inbound"
 access = "Allow"
 protocol = "Tcp"
 source_port_range = "*"
 destination_port_range = "80"
 source_address_prefix = "*"
 destination_address_prefix = "*"
 }
}

This allows HTTP traffic to a web server via NSG.

Conclusion

Cloud Firewalls and NSGs are more than just "rules", they are critical to your cloud architecture's security posture. Whether you're isolating tiers of an application or filtering traffic at the edge, these tools enable flexible, scalable, and automated defense mechanisms.

For students and professionals, mastering these tools is a must-have skill for cloud engineers, DevSecOps practitioners, and cybersecurity analysts.

To take this further with guided labs and an instructor, see our CCSP cloud security certification.

Related reading

• What are the most essential Linux firewalls in 2026 and how do they protect your systems?
• Advanced Linux Firewall Security | Configuring iptables and firewalld for Maximum Protection
• Why Every Business Needs a Web Application Firewall (WAF) in 2026 | Protect Your Web Apps from Modern Cyber Threats

Reference

For the authoritative details, see AWS documentation.