Network Security Groups (NSG) in Azure - Time & Space Complexity

Time Complexity: Network Security Groups (NSG)

O(n + m)

Understanding Time Complexity

When managing Network Security Groups (NSGs), it is important to understand how the time to apply rules grows as you add more rules or associate NSGs with more resources.

We want to know how the number of operations changes when the NSG configuration grows.

Scenario Under Consideration

Analyze the time complexity of applying multiple NSG rules to multiple network interfaces.

# Create NSG
az network nsg create --resource-group MyResourceGroup --name MyNSG

# Add multiple rules
for i in $(seq 1 $n); do
  az network nsg rule create --resource-group MyResourceGroup --nsg-name MyNSG --name Rule$i --priority $((100 + i)) --access Allow --direction Inbound --protocol Tcp --source-address-prefixes '*' --source-port-ranges '*' --destination-address-prefixes '*' --destination-port-ranges 80
done

# Associate NSG to multiple NICs
for j in $(seq 1 $m); do
  az network nic update --resource-group MyResourceGroup --name Nic$j --network-security-group MyNSG
done

This sequence creates one NSG, adds n rules to it, and associates it with m network interfaces.

Identify Repeating Operations

Identify the API calls, resource provisioning, data transfers that repeat.

• Primary operation: Creating NSG rules and associating NSG to NICs.
• How many times: Rule creation happens n times; NIC update happens m times.

How Execution Grows With Input

As you add more rules (n) or associate with more NICs (m), the number of API calls grows linearly with both.

Input Size (n rules, m NICs)	Approx. Api Calls/Operations
10 rules, 10 NICs	~20 calls (10 rule creates + 10 NIC updates)
100 rules, 100 NICs	~200 calls
1000 rules, 1000 NICs	~2000 calls

Pattern observation: Doubling rules or NICs roughly doubles the total operations.

Final Time Complexity

Time Complexity: O(n + m)

This means the time to complete all operations grows directly with the number of rules plus the number of NICs.

Common Mistake

[X] Wrong: "Adding more rules does not affect the time because the NSG is a single resource."

[OK] Correct: Each rule requires a separate API call to create, so more rules mean more operations and more time.

Interview Connect

Understanding how NSG operations scale helps you design efficient network security setups and shows you can reason about cloud resource management in real projects.

Self-Check

What if we grouped multiple rules into fewer NSGs and associated each NSG with fewer NICs? How would the time complexity change?