Public IP addresses in Azure - Deep Dive

Overview - Public IP addresses

What is it?

A public IP address is a unique number assigned to a device or resource on the internet. It allows that device to be found and communicate with other devices worldwide. In cloud computing, public IP addresses let your virtual machines or services connect to and be accessed from the internet. Without a public IP, your resource is hidden from the outside world.

Why it matters

Public IP addresses exist so devices and services can be reached over the internet. Without them, your cloud resources would be isolated and unreachable from outside networks. This would make it impossible to host websites, APIs, or any service that needs to interact with users or other systems globally. They solve the problem of unique identification and routing on the internet.

Where it fits

Before learning about public IP addresses, you should understand basic networking concepts like IP addresses and private networks. After this, you can learn about DNS, load balancers, and network security groups which control access to resources with public IPs.

Mental Model

Core Idea

A public IP address is like a unique phone number that lets anyone on the internet call your cloud resource directly.

Think of it like...

Imagine your cloud resource is a house. The public IP address is the house's street address that anyone can use to send mail or visit. Without this address, no one can find your house from outside the neighborhood.

┌───────────────┐       ┌───────────────┐
│  Internet     │──────▶│ Public IP     │
│ (World Wide)  │       │ Address       │
└───────────────┘       └───────────────┘
                             │
                             ▼
                      ┌───────────────┐
                      │ Cloud Resource│
                      │ (VM, Service) │
                      └───────────────┘

Build-Up - 7 Steps

1

Foundation

What is an IP address

Concept: Introduce the basic idea of IP addresses as unique identifiers for devices on a network.

Every device connected to a network has an IP address, which is a number that identifies it. Think of it like a home address but for computers. There are two main types: private IPs used inside local networks, and public IPs used on the internet.

Result

You understand that IP addresses let devices find and talk to each other.

Understanding IP addresses is the foundation for grasping how devices communicate in any network, including the cloud.

2

Foundation

Difference between private and public IPs

Concept: Explain the distinction between private IPs (local use) and public IPs (internet-wide use).

Private IP addresses are used inside a home or company network and cannot be reached directly from the internet. Public IP addresses are unique across the whole internet and allow devices to be found globally. Cloud resources often have private IPs for internal communication and public IPs to be accessible from outside.

Result

You can tell when a device can be reached only inside a network or from anywhere on the internet.

Knowing this difference helps you design secure and reachable cloud architectures.

3

Intermediate

How Azure assigns public IP addresses

🤔Before reading on: do you think Azure public IPs are permanent by default or can change? Commit to your answer.

Concept: Azure offers two types of public IP addresses: dynamic and static, which differ in how their address can change over time.

Dynamic public IPs are assigned when a resource starts and may change if the resource stops and restarts. Static public IPs are reserved and stay the same for the resource's lifetime. Choosing between them depends on whether you need a fixed address for DNS or certificates.

Result

You know how to pick the right public IP type for your cloud resource's needs.

Understanding IP assignment types prevents connectivity issues and supports stable service endpoints.

4

Intermediate

Public IP address SKU and zones

🤔Before reading on: do you think all Azure public IPs support availability zones? Commit to your answer.

Concept: Azure public IPs come in Basic and Standard SKUs, which differ in features like zone redundancy and security.

Basic SKU public IPs do not support zone redundancy and have limited security features. Standard SKU supports zone redundancy, better security, and is recommended for production workloads. Availability zones help keep your service reachable even if one zone fails.

Result

You can choose the SKU that fits your reliability and security needs.

Knowing SKU differences helps design resilient and secure cloud networks.

5

Intermediate

Using public IPs with Azure resources

Concept: Learn how public IPs connect to Azure resources like virtual machines and load balancers.

You can assign a public IP directly to a virtual machine's network interface to allow direct internet access. Alternatively, you can attach a public IP to a load balancer, which then distributes traffic to multiple private IPs behind it. This setup improves scalability and security.

Result

You understand practical ways to expose cloud services to the internet.

Knowing how to attach public IPs correctly is key to building accessible and scalable cloud applications.

6

Advanced

Security considerations for public IPs

🤔Before reading on: do you think having a public IP automatically means your resource is secure? Commit to your answer.

Concept: Public IPs expose resources to the internet, so security controls like firewalls and network security groups are essential.

Assigning a public IP makes your resource reachable globally, but it also opens it to potential attacks. Azure provides network security groups (NSGs) to control which traffic is allowed. Best practice is to restrict access to only necessary ports and IP ranges, and use additional layers like Azure Firewall or DDoS protection.

Result

You know how to protect your cloud resources even when they have public IPs.

Understanding security risks of public IPs helps prevent breaches and service disruptions.

7

Expert

Public IP address scaling and limits

🤔Before reading on: do you think Azure imposes limits on how many public IPs you can create? Commit to your answer.

Concept: Azure enforces limits on public IP addresses per subscription and region, and scaling considerations affect design choices.

Each Azure subscription has default limits on the number of public IPs you can create, which can be increased by request. Large-scale applications often use load balancers or Azure Front Door to minimize the number of public IPs needed. Understanding these limits helps plan cost and architecture for growth.

Result

You can design cloud networks that scale efficiently without hitting resource limits.

Knowing Azure public IP limits and scaling patterns prevents costly redesigns and outages.

Under the Hood

Public IP addresses in Azure are allocated from a global pool of unique IPv4 or IPv6 addresses. When you create a public IP resource, Azure reserves an address and maps it to your cloud resource's network interface or load balancer. Traffic from the internet to that IP is routed through Azure's network fabric to your resource. Azure manages address translation and routing internally to ensure uniqueness and reachability.

Why designed this way?

Azure designed public IPs as separate resources to allow flexible assignment, reuse, and management independent of compute resources. This separation supports dynamic cloud environments where resources can be created, deleted, or moved without losing their public identity. The SKU and zone options reflect the need for reliability, security, and compliance in enterprise cloud deployments.

┌───────────────┐       ┌───────────────┐       ┌───────────────┐
│  Internet     │──────▶│ Azure Public  │──────▶│ Cloud Resource│
│ (Clients)    │       │ IP Address    │       │ (VM, LB, etc) │
└───────────────┘       └───────────────┘       └───────────────┘
         ▲                      │                      │
         │                      ▼                      ▼
   Incoming traffic      Azure Network Fabric   Resource Network Interface

Myth Busters - 4 Common Misconceptions

Quick: Does assigning a public IP to a VM automatically make it secure? Commit to yes or no.

Common Belief: If a VM has a public IP, it is safe because Azure protects it by default.

Reality: Assigning a public IP only makes the VM reachable; security depends on additional controls like firewalls and NSGs.

Why it matters: Assuming default safety can lead to exposed services vulnerable to attacks.

Quick: Do dynamic public IPs keep the same address forever? Commit to yes or no.

Common Belief: Dynamic public IP addresses never change once assigned.

Reality: Dynamic public IPs can change if the resource is stopped and restarted.

Why it matters: Relying on dynamic IPs for DNS or certificates can cause connectivity failures.

Quick: Can you assign the same public IP to multiple VMs directly? Commit to yes or no.

Common Belief: You can assign one public IP to many VMs to save addresses.

Reality: Each public IP can only be assigned to one resource; to share, use a load balancer.

Why it matters: Trying to share a public IP directly causes configuration errors and unreachable services.

Quick: Are all Azure public IPs zone redundant by default? Commit to yes or no.

Common Belief: All Azure public IP addresses automatically support availability zones.

Reality: Only Standard SKU public IPs support zone redundancy; Basic SKU does not.

Why it matters: Choosing the wrong SKU can reduce availability and resilience.

Expert Zone

1

Standard SKU public IPs require explicit inbound and outbound rules in NSGs, unlike Basic SKU which allows default inbound traffic.

2

Public IP addresses can be reserved and associated with resources later, enabling flexible deployment workflows.

3

Azure supports both IPv4 and IPv6 public IPs, but IPv6 is less commonly used and has different routing considerations.

When NOT to use

Public IP addresses are not suitable for internal-only services or sensitive data that should not be exposed. Instead, use private IPs with VPN or ExpressRoute for secure private connectivity. For global scale and performance, consider Azure Front Door or CDN which use public IPs but add caching and security layers.

Production Patterns

In production, public IPs are often assigned to load balancers or application gateways rather than individual VMs to improve scalability and security. Static Standard SKU IPs are preferred for stable DNS and compliance. Network security groups and Azure Firewall are layered to tightly control traffic. Monitoring and alerting on public IP usage helps detect attacks or misconfigurations.

Connections

Domain Name System (DNS)

Builds-on

Public IP addresses provide the numeric location, while DNS translates friendly names to these IPs, enabling easy access to cloud services.

Network Address Translation (NAT)

Complementary

NAT allows multiple private IPs to share a single public IP for outbound traffic, helping conserve public IPs and add security layers.

Telephone Numbering System

Analogous system in telecommunications

Just as telephone numbers uniquely identify phones worldwide, public IP addresses uniquely identify devices on the internet, enabling global communication.

Common Pitfalls

#1 Assigning a dynamic public IP when a static IP is needed for DNS.

Wrong approach:

az network public-ip create --name myPublicIP --resource-group myRG --allocation-method Dynamic

Correct approach:

az network public-ip create --name myPublicIP --resource-group myRG --allocation-method Static

Root cause:

Misunderstanding that dynamic IPs can change, causing DNS records to become invalid.

#2 Exposing a VM with a public IP but no network security group rules.

Wrong approach:

Assign public IP to VM and leave NSG with default allow all inbound.

Correct approach:

Assign public IP and configure NSG to allow only required ports and IP ranges.

Root cause:

Assuming Azure automatically secures public IPs without explicit firewall rules.

#3 Trying to assign the same public IP to multiple VMs directly.

Wrong approach:

Assign one public IP resource to multiple VM NICs.

Correct approach:

Assign unique public IPs to each VM or use a load balancer with one public IP.

Root cause:

Not knowing public IP resources are one-to-one with network interfaces.

Key Takeaways

Public IP addresses uniquely identify cloud resources on the internet, enabling global access.

Azure offers dynamic and static public IPs; static ones provide stable addresses needed for DNS and certificates.

Security is critical when using public IPs; network security groups and firewalls must control traffic.

Choosing the right SKU and understanding Azure limits ensures reliable and scalable cloud deployments.

Public IPs work together with DNS and NAT to provide flexible, secure, and reachable cloud networking.