Azure Application delivery: which load balancing service to choose?

The transition to cloud solutions to deliver applications is a trend that is proceeding at a very fast pace and ensuring an access fast, secure and reliable to such applications is a challenging task that must be directed by adopting the right solutions. Microsoft Azure provides a wide range of services to ensure optimal application delivery, but in assessing which load-balancing solution to adopt there are several aspects to consider. This article wants to clarify what you should consider to adopt the most suitable Azure solution in this area.

The need to distribute workloads over multiple computing resources may be due to the need to optimize the use of resources, maximize throughput, minimize response times and avoid overloading every single resource. Furthermore, it can also be aimed at improving application availability by sharing a workload between redundant computing resources.

Azure load balancing services

To provide Azure load-balancing services we find the following components.

Azure Load Balancer and cross-region Azure Load Balancer: these are components that enable Layer-4 load balancing for all TCP and UDP protocols, ensuring high performance and very low latencies. Azure Load Balancer is a component zone-redundant, therefore provides high availability among availability zones.

Figure 1 – Azure Load Balancer and cross-region Azure Load Balancer overview

Azure Application Gateway: it is a service managed by the azure platform, with inherent features of high availability and scalability. The Application Gateway is a application load balancer (OSI layer 7) for web traffic, that allows you to govern HTTP and HTTPS applications traffic (URL path, host based, round robin, session affinity, redirection). The Application Gateway is able to centrally manage certificates for application publishing, using SSL and SSL offload policy when necessary. The Application Gateway may have assigned a private IP address or a public IP address, if the application must be republished in Internet. In particular, in the latter case, it is recommended to turn onWeb Application Firewall (WAF), that provides application protection, based on rulesOWASP core rule sets. The WAF protects the application from vulnerabilities and against common attacks, such as X-Site Scripting and SQL Injection attacks.

Figure 2 – Azure Application Gateway Overview

Front Door: is an application delivery network that provides global load balancing and site accelleration service for web applications. It offers Layer-7 functionality for application publishing such as SSL offload, path-based routing, fast failover, caching, in order to improve the performance and high availability of applications.

Figure 3 – Azure Front Door Overview

Traffic Manager: is a DNS-based load balancer that enables optimal distribution of traffic to services deployed in different Azure regions, while providing high availability and responsiveness. Are available different routing methods to determine which endpoint to direct traffic to. Based on DNS, failover may not be immediate due to common challenges related to DNS caching and systems not meeting DNS TTLs.

Figure 4 – Azure Traffic Manager Overview (performance traffic-routing method)

Things to consider when choosing Azure load balancing services

Each service has its own characteristics and to choose the most appropriate one it is good to make a classification with respect to the following aspects.

Load-balancing services: global vs regional

  • Global load-balancing: are used to distribute traffic to globally distributed backends across multiple regions, which can be deployed in cloud or hybrid environments. Fall into this category Azure Traffic Manager, Azure Front Door and the cross-region Azure Load Balancer.
  • Regional load-balancing: they allow you to distribute traffic to virtual machines connected to a specific virtual network or to endpoints in a specific region. This category includes Azure Load Balancer and the Azure Application Gateway.

Type of traffic: HTTP(S) vs non-HTTP(S)

Another important differentiating factor in the choice of the load-balancing solution to be adopted is the type of traffic that must be managed:

  • HTTP(S): the adoption of Layer-7 load-balancing services that accept only HTTP traffic is recommended(S). They are suitable for this type of traffic Azure Front Door and Azure Application Gateway. Typically they are used for web applications or other endpoints HTTP (S) and include features such as: SSL offload, web application firewall, path-based load balancing, and session affinity.
  • Non-HTTP(S): the use of load-balancing services is required that allow to contemplate the traffic non-HTTP (S), such as Azure Traffic Manager, cross-region Azure Load Balancer and Azure Load Balancer.

In the evaluation of the Azure load-balancing service to be adopted, it is also appropriate to include considerations regarding the following aspects:

To facilitate the choice of the load-balancing solution, the following flow chart can be used as a starting point, which directs the choice on a series of key aspects:

Figure 5 – Flowchart for choosing azure load-balancing solution

Note: This flowchart does not cover the cross-region Azure Load Balancer as at the moment (11/2020) are in preview.

This flow chart is a great starting point for your evaluations, but since each application has unique requirements it is good to carry out a specific more detailed analysis.

If the application consists of multiple workloads, it is appropriate to evaluate each of these separately, as it may be necessary to adopt one or more load balancing solutions.

The various load load-balancing services can be used in combination with each other to ensure reliable and secure application access to the services provided in environments IaaS, PaaS or on-premises.

Figure 6 – Possible example of how to combine the various Azure load-balancing services

Conclusions

Thanks to a wide range of global and regional services, Azure is able to guarantee performance, security and high availability in application access. In order to establish the architecture that best meets your needs, there are several elements to evaluate, but the right combination of Azure Application Delivery solutions can deliver significant value to IT organizations, ensuring a distribution that is fast, secure and reliable for applications and user data.

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