How do you implement hybrid connectivity between your on-premises network and Azure IaaS ?

Implementing hybrid connectivity between your on-premises network and Azure IaaS involves establishing a secure link to your Azure Virtual Network. The primary methods are using an Azure VPN Gateway for secure, encrypted connections over the public internet, or Azure ExpressRoute for dedicated, private connections offering higher performance and reliability. The optimal choice depends on your specific performance, security, and cost requirements.

Introduction to Azure Hybrid Connectivity

In today’s cloud-centric world, many organizations adopt a hybrid cloud strategy, extending their on-premises infrastructure into public clouds like Microsoft Azure. This requires robust and secure hybrid connectivity, allowing seamless communication between your existing data centers and your Azure-hosted Infrastructure-as-a-Service (IaaS) resources, such as virtual machines and applications. This guide explores the key methods and considerations for achieving this vital connection.

Core Azure Networking Component: The Virtual Network (VNet)

At the heart of Azure IaaS networking is the Azure Virtual Network (VNet). An Azure VNet provides a logically isolated network segment within Azure, where your virtual machines and other resources reside. All hybrid connectivity solutions connect to this VNet, enabling your on-premises network to communicate with your cloud resources as if they were part of the same extended network.

For instance, the Azure VNet is foundational to our Azure infrastructure. We use it to segment our resources, creating separate VNets for production, development, and testing. Our VMs reside within these VNets, and both our VPN Gateway and ExpressRoute circuits connect to the production VNet, allowing secure communication between our on-premises network and our Azure resources.

Primary Hybrid Connectivity Options

1. Azure VPN Gateway: Secure Connectivity Over the Internet

The Azure VPN Gateway is a cost-effective solution that establishes secure, encrypted connections over the public internet. It’s ideal for organizations with smaller deployments or less demanding bandwidth needs.

How it Works:

A VPN Gateway creates a secure tunnel (specifically, a Site-to-Site VPN) between your on-premises network and your Azure VNet. Data transmitted through this tunnel is encrypted, ensuring its confidentiality and integrity even while traversing the public internet. This connection acts like a secure tunnel, allowing your on-premises servers and users to access resources in Azure as if they were on the same local network.

Use Case Example:

In a previous project, we had a small branch office that needed access to resources running in our Azure VNet. An Azure VPN Gateway was the perfect fit. It provided a secure, encrypted connection over the internet without the expense of a dedicated line. We configured the VPN Gateway in Azure and a compatible VPN device on-premises, and the connection was up and running quickly, providing the branch office with the necessary access.

2. Azure ExpressRoute: Dedicated, Private Connectivity

Azure ExpressRoute provides a dedicated, private connection between your on-premises network and Azure, offering higher bandwidth, lower latency, and greater reliability compared to internet-based VPNs. Crucially, ExpressRoute bypasses the public internet, making it suitable for mission-critical applications and large data transfers.

How it Works:

ExpressRoute connections are facilitated by ExpressRoute circuits, which represent the physical connections provided by your chosen connectivity provider (e.g., a telecom company). This dedicated circuit extends your on-premises network directly into Microsoft’s global network, connecting to your Azure VNet. Our ExpressRoute circuit represents the physical fiber connection provided by our telecom provider. This dedicated connection ensures consistent performance and low latency for our mission-critical applications.

Use Case Example:

When we migrated our core financial application to Azure, we needed a high-performance, reliable connection. ExpressRoute was the obvious choice. We worked with our telecom provider to establish a dedicated circuit to our Azure VNet. This bypassed the public internet, providing the low latency and high bandwidth required by our application.

Advanced Considerations for Hybrid Connectivity

When designing and implementing your hybrid connectivity solution, consider the following aspects:

1. VPN Types and Dynamic Routing with BGP

For VPN Gateways, it’s important to understand the difference between policy-based VPNs and route-based VPNs.

• Policy-based VPNs are generally simpler to configure but are less flexible, as they require explicit policies for each traffic flow.
• Route-based VPNs offer greater flexibility and are commonly used with BGP (Border Gateway Protocol). BGP enables dynamic routing, allowing your on-premises network and Azure to automatically exchange routing information. This simplifies network management, enhances scalability, and provides automatic failover capabilities in case of a network outage, which is crucial for business continuity.

We initially used a policy-based VPN for our hybrid connectivity. It was easy to set up, but as our network grew, we found it increasingly difficult to manage the complex access policies. We then switched to a route-based VPN, which allowed us to leverage BGP for dynamic routing. This significantly simplified network management and provided automatic failover capabilities. For our ExpressRoute connection, BGP is essential. It dynamically exchanges routing information between our on-premises network and Azure, ensuring that traffic is always routed optimally and providing automatic failover.

2. ExpressRoute Connectivity Models

Azure ExpressRoute offers several connectivity models to suit different architectural needs. Showing an understanding of these models will impress interviewers.

• Cloud Exchange Colocation: Connect to Azure via a cloud exchange provider, ideal if you’re already colocated in a data center with such a presence. This offers a seamless and cost-effective way to connect.
• Point-to-Point Ethernet Connection: Establish a direct, dedicated Ethernet connection from your on-premises site to a Microsoft peering location.
• Any-to-Any (IPVPN) Connection: Connect to Azure via your existing MPLS VPN network, suitable if you need to connect multiple on-premises locations to Azure through a single managed service.

We evaluated the different ExpressRoute connectivity models when setting up our dedicated connection. Since we were already colocated in a data center with a Cloud Exchange presence, the Cloud Exchange Colocation model was the most suitable. It provided a seamless and cost-effective way to connect to Azure. However, if we weren’t colocated, we would have considered the Point-to-Point Ethernet Connection for direct connectivity or the Any-to-Any (IPVPN) Connection if we needed to connect multiple on-premises locations to Azure.

3. Security Considerations: Firewalls and Network Security Groups (NSGs)

Security is paramount for any hybrid connectivity solution. You must implement robust security considerations on both your on-premises and Azure sides.

• Azure Side: Utilize Network Security Groups (NSGs) to control traffic flow to your Azure VMs and subnets. NSGs act as a firewall at the virtual network level, allowing you to define rules that allow only necessary traffic from your on-premises network while blocking unauthorized access.
• On-premises Side: Leverage your existing firewalls to restrict traffic destined for Azure. This creates a layered security approach, ensuring that your hybrid connection is protected from unauthorized access from both ends.

This combination of on-premises and cloud-based security measures ensures that our hybrid connection is protected from unauthorized access.

Conclusion

Choosing between Azure VPN Gateway and ExpressRoute depends on your organization’s specific requirements for bandwidth, latency, reliability, and cost. While VPN Gateways offer a flexible and cost-effective way to establish secure connections over the internet, ExpressRoute provides a dedicated, high-performance private link for mission-critical workloads. Regardless of your choice, a thorough understanding of Azure networking components and security best practices is essential for a successful hybrid cloud deployment.

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