Blue Skies

Implementing and Managing IPs

Azure allows Linux VMs to be assigned both public and private IP addresses, each serving different purposes within a network architecture. Properly managing these IPs is important for maintaining security and ensuring that applications are accessible as intended.

Private IP addresses are used for internal communication within a VNet, making them important for services that need to interact with other VMs, databases, or services, without exposing them to the public Internet. In contrast, public IP addresses are used to expose specific services or applications to the Internet, making them accessible from anywhere.

When assigning public IP addresses, it is important to consider security implications. Public IPs should be limited to only those VMs that require external access, such as web servers or VPN gateways. Additionally, the use of NSGs for tight control of inbound and outbound traffic on public IP addresses helps mitigate risks associated with exposure to the Internet.

On the other hand, private IPs should be carefully managed to ensure proper internal communication by making certain IP address ranges do not overlap with on-premises networks (if connected over a VPN or ExpressRoute) and routing is configured correctly to handle traffic between different subnets and VNets. Azure provides features like Private Link and VNet peering to extend the utility of private IPs, enabling secure connections between different Azure services or between Azure and on-premises environments without the need for a public IP.

For scenarios in which high availability and load balancing are required, public and private IPs can be used in conjunction with Azure Load Balancer. For instance, a web application might use a public IP address as the front end for incoming traffic, whereas the back-end VMs communicate by private IPs within a secure VNet. This setup not only enhances security but also improves performance by localizing traffic and reducing the attack surface.

Traffic Management

Effective traffic management is important for maintaining the performance, availability, and security of Linux-based applications hosted on Azure. Azure provides a suite of tools that allows IT professionals to implement strong traffic management strategies, ensuring that applications remain responsive and resilient under varying loads and conditions. Key tools in this suite include the Azure Load Balancer, Azure Application Gateway, and Azure Traffic Manager, each of which plays a distinct role in managing traffic for Linux environments.

Configuring for High Availability

The Azure Load Balancer (Figure 4) is a foundational component for achieving high availability in Linux-based environments. It operates at the transport layer (Layer 4) and is designed to distribute incoming network traffic across multiple VMs within a VNet, ensuring that no single VM becomes a bottleneck or point of failure.

Figure 4: Configuration of a front-end IP for a load balancer in Azure.

When configuring the Azure Load Balancer for Linux workloads, it's important to consider both internal and external load-balancing needs. Internal load balancing is typically used to distribute traffic among VMs within a private VNet, which is common for back-end services such as databases or internal APIs. External load balancing, on the other hand, distributes traffic from the Internet to VMs within a VNet, which is often used for public-facing web servers or applications.

To set up a load balancer, you define a front-end IP configuration, back-end pool, and load-balancing rules. The front-end IP configuration is the entry point for incoming traffic, which the load balancer then distributes to the VMs in the back-end pool according to the defined rules. These rules determine how traffic is distributed, such as by source IP, protocol, or port.

For high availability, it's important to include multiple VMs in the back-end pool, ideally spread across different availability zones or availability sets. This configuration ensures that if one VM or zone experiences an outage, the load balancer can continue directing traffic to the remaining healthy VMs, maintaining the availability of the application.

Additionally, leveraging health probes is important for ensuring that only healthy VMs receive traffic. Health probes periodically check the health status of each VM in the back-end pool. If a VM fails the health check, the load balancer automatically stops directing traffic to that VM until it is back online, thus preventing service interruptions.