Azure Firewall vs NSGs – When and Why to Use Both

Ah yes, Azure Firewall vs NSGs. The Clash of the Titans. The WWE SmackDown nobody asked for, but everyone building anything in Azure eventually gets dragged into.

If you’ve ever found yourself wondering:

• “Do I actually need Azure Firewall?”

• “Aren’t NSGs basically mini firewalls?”

• “Why does Azure have 47 different network security controls, and why do they all overlap just enough to confuse me?”

…then congratulations, you’re officially living the cloud security dream. Grab your beverage of choice and let’s unpack this together.

Why This Even Matters

In Azure, your network security toolbox comes with two big players:

• NSGs – the lightweight, dependable, slightly underappreciated guardians of your subnets and NICs.

• Azure Firewall – the enterprise-grade security appliance that shows up wearing sunglasses indoors and talking about “threat intelligence mode.”

Both handle traffic filtering. Both are stateful. Both are important. But they are not interchangeable unless your idea of fun is rebuilding half your infrastructure at 2 a.m. because someone assumed they were.

What Is an NSG? (Your Friendly Neighborhood Bouncer)

Picture an NSG as the bouncer at a nightclub.

Simple. Practical. Cheap. Checks IDs (source IP), controls who gets in (rules), and works the door at either the subnet or NIC level.

It doesn’t pretend to be fancy. It does its job. It doesn’t ask for much. Honestly? A king.

NSGs Can:

• Block or allow traffic based on IPs and ports

• Provide micro-segmentation inside your VNet

• Filter east-west traffic

• Keep internal traffic sane

• Do all this for free (Azure’s greatest gift)

NSGs Cannot:

• Block URLs

• Inspect traffic

• Do application-level filtering

• Stop known malicious IPs

• Fix your developer’s “allow all outbound because dev environment” rule

What Is Azure Firewall? (Your Corporate Bodyguard With the Expensive Sunglasses)

Now think of Azure Firewall as the top-tier private security force.

It’s the bodyguard who stands outside a fancy corporate building, wearing a crisp suit, monitoring 17 screens at once, and charging you by the hour (plus extra per GB).

Azure Firewall isn’t just a gatekeeper, it’s a whole perimeter strategy.

Azure Firewall Can:

• Filter L3–L7 traffic

• Inspect web traffic

• Block malicious IPs automatically using threat intel

• Do FQDN and domain-level filtering

• Perform TLS inspection

• Provide centralised outbound internet control

• Log absolutely everything (and sometimes too much)

Azure Firewall Cannot:

• Be cheap

• Be subtle

• Be something you install “just because”

So… Which One Should You Use?

Plot twist: you almost always use both.

Using Azure Firewall without NSGs is like having high-security guards at the front door but leaving every internal office door unlocked.

Using NSGs without Azure Firewall is like locking every internal door but leaving the front door wide open because “it’s probably fine.”

They aren’t alternatives. They’re teammates. Like toast & butter. Like Terraform & the stack you forgot to destroy. Like DevOps & existential dread.

When to Use NSGs

NSGs are perfect for:

• Internal segmentation (aka “east-west traffic control”)

• Restricting VM-to-VM communication

• Protecting subnets from accidental lateral movement

• Applying least privilege rules at the subnet/NIC level

• Preventing that one container from talking to literally everything

Their superpower is being lightweight, simple, and everywhere you need them.

When to Use Azure Firewall

Azure Firewall shines when you need:

• Centralized outbound filtering

• URL/FQDN filtering

• Threat intelligence

• Guardrails for internet access

• A perimeter around your hub VNet

• Application-level controls

• Fancy enterprise security features with fancy enterprise pricing

Its real strength? Being the single, controlled choke point for all north-south traffic.

The Magic Combo: Using Azure Firewall + NSGs

This is where network security gets good.

Hub-and-Spoke? Use Both.

Azure Firewall in the hub handles the perimeter. NSGs on spokes handle the internal chatter.

Zero Trust Architecture? Use Both.

Firewall handles what gets in/out. NSGs limit who can talk to who.

Outbound Internet Control? Use Both.

Firewall decides what destinations you can hit. NSGs decide what internal services can reach the firewall to begin with.

It’s a partnership. A dynamic duo. The cloud security Avengers, minus the licensing drama.

Cost Talk (Don’t Panic)

• NSGs are free.

• Azure Firewall is… not. Like “budget meeting next quarter” not.

But here’s the truth: If you actually need what Azure Firewall does, nothing else in Azure does it as cleanly or centrally. You’re paying for simplicity + control + logging that won’t make your SOC cry.

Best Practices (AKA Advice Future-You Will Be Grateful For)

• Use NSGs everywhere, they’re free and effective.

• Put Azure Firewall in your hub if you’re doing multi-VNet.

• Always enable NSG Flow Logs.

• Use Firewall Manager if you have multiple firewalls.

• Never deploy TLS inspection in production without testing it on something you don’t like first.

• Keep NSGs tight and simple: fewer rules, more clarity.

Conclusion

Azure Firewall and NSGs aren’t rivals. They’re complementary tools solving different parts of the network security puzzle.

NSGs secure your internal world. Azure Firewall secures your perimeter and outbound connectivity.

Use both, and you’ve got a strong, scalable, Zero-Trust-ready environment. Use only one, and you’ll find yourself asking, “Why is this traffic allowed again?”

Next time someone on your team boldly claims, “We don’t need both, just pick one!”

Just send them this blog. Politely. Or aggressively. Your choice.