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

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
• Frequently Asked Questions (FAQs)

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.

FAQs

What is a Cloud Firewall?

A cloud firewall is a security service that protects cloud-based infrastructure by filtering and monitoring traffic entering and exiting the network.

How do Network Security Groups (NSGs) work in Azure?

NSGs act like virtual firewalls that control inbound and outbound traffic to Azure resources based on defined rules.

What is the difference between NSG and cloud firewall?

NSGs operate at the subnet or NIC level, whereas cloud firewalls provide broader network-level security and advanced filtering capabilities.

Are AWS Security Groups similar to Azure NSGs?

Yes, both function similarly by controlling traffic to and from cloud resources using rule-based access.

How do you apply NSGs in a multi-tier architecture?

Assign NSGs at each layer (web, app, DB) with specific rules to segment and protect workloads within each tier.

What is an ACL in cloud networking?

An Access Control List (ACL) defines rules that allow or deny traffic to resources based on IP addresses, protocols, and ports.

Can NSGs be used for outbound traffic control?

Yes, NSGs in Azure allow for both inbound and outbound traffic rule configuration.

What is a stateless vs stateful firewall in cloud?

A stateless firewall treats each packet independently, while a stateful firewall tracks sessions and connection states.

Does Google Cloud use NSGs?

Google Cloud uses firewall rules with similar functionality to NSGs in Azure and Security Groups in AWS.

Why is defense in depth important in the cloud?

It ensures that if one layer is breached, multiple other controls protect critical assets.

What is a perimeter firewall in cloud architecture?

A perimeter firewall controls traffic between the internet and your cloud VPCs or networks.

How do cloud firewalls support compliance?

They help enforce security controls, logging, and segmentation required by standards like ISO 27001, HIPAA, and PCI DSS.

Can NSGs block malicious IPs?

Yes, NSGs can deny traffic from specific IP addresses or ranges using custom rules.

What is zone-based security in cloud?

It segments environments into zones (public, private, DMZ) with varying levels of access and applies firewalls accordingly.

Can I use both NSGs and firewalls together?

Yes, combining NSGs and cloud firewalls enhances security by enforcing policies at multiple layers.

What is an example of NSG rule for a web server?

Allow inbound traffic on port 80/443 from internet sources; deny all other inbound connections.

Is there a managed cloud firewall service?

Yes, all major clouds offer managed firewall services like Azure Firewall, AWS Network Firewall, and GCP Cloud Firewall.

How do I monitor NSG traffic logs?

Enable NSG flow logs in Azure or use CloudWatch in AWS to track and analyze traffic patterns.

What is a DMZ in cloud networking?

A Demilitarized Zone (DMZ) is a buffer zone that contains externally facing services while protecting the internal network.

How are NSGs different from UDRs (User-Defined Routes)?

NSGs filter traffic, while UDRs define the path that traffic should take.

What is an example of layered firewall architecture?

Use perimeter firewalls at VPC edge, NSGs at subnet level, and workload-level agents for deep inspection.

Can I automate NSG rule creation?

Yes, you can use Terraform, Bicep, or Azure CLI to script and automate NSG configurations.

What are default rules in NSGs?

NSGs come with default rules (like deny all inbound, allow all outbound) that can be overridden with custom rules.

What happens if no NSG is applied?

If no NSG is assigned, the resource might be left unprotected unless higher-level firewalls or controls exist.

How do security groups in AWS work?

They act as virtual firewalls for EC2 instances, controlling inbound and outbound traffic.

Are NSGs region-specific?

NSGs are resource group-specific and can be applied to resources within a subscription, regardless of region.

What are common mistakes in configuring NSGs?

Leaving open ports, allowing unrestricted access (0.0.0.0/0), or overlapping rules can expose workloads.

Can I prioritize NSG rules?

Yes, Azure NSGs use a priority number where lower values take precedence.

Are cloud-native firewalls enough for security?

They’re a critical layer, but combining them with IDS/IPS, WAF, and zero trust adds complete protection.