Virtual Network Architecture
Designing a robust and scalable Azure Virtual Network (VNet) architecture is crucial for modern cloud deployments. This document outlines key architectural patterns, best practices, and considerations for building effective VNets.
Core Concepts
An Azure Virtual Network is the fundamental building block for your private network in Azure. It represents your own network in the cloud, allowing you to:
- Provision and manage Azure resources privately.
- Connect Azure resources to each other.
- Connect Azure resources to the internet.
- Connect Azure resources to your on-premises networks.
Architectural Patterns
1. Hub-and-Spoke Architecture
The hub-and-spoke model is a widely adopted pattern for VNet architecture in Azure. It consists of a central Virtual Network (the hub) that connects to multiple other Virtual Networks (the spokes) through VNet peering or a Network Virtual Appliance (NVA).
- Hub VNet: Typically contains shared services such as firewalls, VPN gateways, DNS servers, and NAT gateways. It acts as a central transit point.
- Spoke VNets: Contain workloads and applications. They are isolated from each other but can communicate with the hub and, through the hub, with other spokes or on-premises networks.
Benefits:
- Centralized security and management.
- Simplified connectivity management.
- Scalability and isolation.
Conceptual diagram of a Hub-and-Spoke VNet architecture.
2. Centralized Connectivity with Shared Services
This pattern focuses on centralizing critical network services like Internet access, DNS resolution, and security enforcement in a dedicated hub VNet. Spoke VNets then connect to this hub to leverage these services.
Key components:
- Hub VNet: Houses Azure Firewall or third-party NVAs for traffic inspection, Azure DNS Private Resolver, and NAT Gateways for outbound internet connectivity.
- Spoke VNets: Deploy applications and services. Traffic is routed through the hub for security and shared services.
3. Distributed VNet Architecture
In scenarios requiring high levels of isolation or specific regional deployments, a distributed VNet architecture might be considered. Each region or business unit might have its own independent VNet architecture, with controlled connectivity between them.
Considerations:
- Requires careful planning for inter-VNet communication and shared services.
- Can be more complex to manage globally.
Key Design Considerations
IP Addressing Scheme
Plan your IP address space carefully to avoid overlaps and accommodate future growth. Use private IP address ranges (RFC 1918). Consider using larger address spaces for the hub VNet to accommodate future expansion of spokes and on-premises connectivity.
RFC 1918 Private Address Ranges:
10.0.0.0 - 10.255.255.255 (10/8 prefix)
172.16.0.0 - 172.31.255.255 (172.16/12 prefix)
192.168.0.0 - 192.168.255.255 (192.168/16 prefix)
Subnetting Strategy
Divide your VNet into subnets to organize resources logically and apply network security policies. Common subnetting strategies include:
- By application tier (e.g., Web, Application, Database).
- By environment (e.g., Development, Staging, Production).
- By security zone.
Ensure subnets are appropriately sized and avoid overlapping IP ranges within the same VNet.
Connectivity
- VNet Peering: Lightweight, low-latency, bidirectional connectivity between two Azure VNets. Ideal for connecting spokes to hubs or other spokes directly.
- VPN Gateway: Connects your on-premises networks to Azure VNets over the public internet or private connections.
- ExpressRoute: Provides a private, dedicated connection between your on-premises infrastructure and Azure.
Security
- Network Security Groups (NSGs): Stateful packet filtering to control inbound and outbound traffic to and from network interfaces and subnets.
- Azure Firewall: A managed, cloud-based network security service that protects your Azure Virtual Network resources.
- Azure DDoS Protection: Provides enhanced DDoS mitigation capabilities.
High Availability and Disaster Recovery
Design your VNet architecture with HA/DR in mind:
- Deploy resources across multiple Availability Zones or Regions.
- Use VNet peering or VPN Gateways for inter-region connectivity.
- Implement load balancing solutions.
Example Scenario: Multinational Corporation
A multinational corporation might implement a global VNet architecture using a hub-and-spoke model across different Azure regions. Each region could have a hub VNet connecting to local spoke VNets for regional applications. Global connectivity might be achieved through peering between regional hubs or via an ExpressRoute circuit terminating in a central hub.
Further Reading: