Azure Firewall $$$$ with Azure App Services Linux: Is It Really Needed?

Azure Firewall with Azure App Services Linux: Is It Really Needed?

When managing cloud security, businesses often wonder if deploying Azure Firewall alongside Azure App Services (Linux) within a VNet is necessary. While security is a top priority, it’s essential to evaluate whether Azure Firewall truly adds value or if built-in security features of Azure App Services and other Azure security mechanisms are sufficient.

Understanding Azure App Services (Linux) Security

Azure App Services (Linux) running inside a Virtual Network (VNet) already benefit from multiple built-in security features that significantly reduce the need for Azure Firewall. Let’s explore what’s included:

1. Private Network Isolation with VNet Integration

• When integrated into a VNet, Azure App Services do not expose a public IP by default.
• You can force all outbound traffic to remain inside the VNet, ensuring isolation from the public internet.
• Using Private Endpoints, the App Service can be accessible only through the VNet.

💡 Why It Matters: If your App Services are privately routed, there’s no need for Azure Firewall to filter external traffic.

2. Network Security Groups (NSGs) for Free Traffic Filtering

• NSGs provide Layer 3 & Layer 4 filtering for inbound and outbound traffic.
• Rules can allow or deny access to resources within the VNet.
• NSGs are free and work without requiring Azure Firewall.

💡 Why It Matters: If your security needs are limited to internal traffic restrictions, NSGs are a cost-effective alternative to Azure Firewall.

3. Built-in TLS, Web Security, and WAF Protection

• Azure App Services support managed TLS/SSL encryption (TLS 1.2/1.3).
• Azure Front Door WAF can be deployed to provide application-layer protection against threats like SQL Injection and XSS.
• If Front Door isn’t used, Azure Application Gateway WAF offers a similar solution at a lower cost than Azure Firewall.

💡 Why It Matters: If the goal is web security, Azure WAF solutions are better suited than Azure Firewall.

4. Private Link and Secure Outbound Access

• Private Endpoints allow App Services to securely connect to Azure services without needing a public IP.
• Custom Route Tables (UDRs) can control outbound flows without a firewall.

💡 Why It Matters: With Private Link, App Services can communicate securely without routing through Azure Firewall.

When Do You Still Need Azure Firewall?

While most deployments won’t require Azure Firewall, some specific scenarios may still justify its use:

✅ Centralized Outbound Security & Traffic Monitoring: If you need to enforce outbound filtering, logging, and centralized security monitoring, Azure Firewall can act as an egress control point.

✅ Layer 3 & Layer 4 Filtering for External APIs: If App Services must interact with external APIs, Azure Firewall can provide protocol-level filtering (but NSGs can also achieve this).

✅ Compliance & Governance Requirements: If regulatory compliance explicitly requires a dedicated network firewall for security audits, Azure Firewall might be needed.

How to Reduce Costs and Avoid Unnecessary Azure Firewall Usage

If you’re currently running Azure Firewall with App Services in a VNet and want to optimize costs, consider the following:

1️⃣ Remove Azure Firewall If It’s Unnecessary – If Azure Front Door WAF is handling security, remove Azure Firewall to save $800+/month.

2️⃣ Use NSGs Instead – NSGs provide free inbound/outbound traffic filtering inside a VNet without the cost of Azure Firewall.

3️⃣ Reduce Firewall Active Hours – If required, schedule Azure Firewall to run only during peak business hours, cutting costs by 50%+.

4️⃣ Move to Private Endpoints – Ensure outbound traffic is routed securely via Private Endpoints instead of going through Azure Firewall.

Final Verdict: Do You Really Need Azure Firewall?

💡 For most Azure App Service (Linux) deployments in a VNet, Azure Firewall is NOT required.

• If Azure Front Door WAF or Application Gateway WAF is in place, web security is already covered.
• If only internal traffic filtering is needed, NSGs and Private Endpoints are free and sufficient.
• Only deploy Azure Firewall if compliance or outbound security monitoring explicitly requires it.

🚀 Take Action: Review your Azure Firewall costs and traffic logs today—you might be able to remove it and save hundreds of dollars per month!