High Availability Load Balancing: What Is It? | Parallels Insights!

What Is High Availability Load Balancing? 

high availability load balancingHigh availability load balancing (HALB) is crucial in preventing potentially catastrophic component failures. Central to this concept is the use of a system of primary and secondary load balancers to automatically distribute workloads across your data centers. This redundancy in both your load balancers and servers ensures near-continuous application delivery. In such a system, when either a load balancer or server fails, corresponding backup equipment takes its place.

Understanding how Load Balancers Work 

Load balancers distribute workloads between servers so that not one server gets overloaded with requests. While routing traffic, load balancers also monitor the health of each server. When thedetect impending signs of server failure, they reroute the traffic to another server. This ensures that your system remains responsive and available no matter the number of server requests. 

Load balancers use session persistence to prevent performance issues and transaction failures in applications such as shopping carts, where multiple session requests are normalWith session persistence, load balancers are able to send requests belonging to the same session to the same server.  

Load balancers can also decrypt SSL traffic prior to passing the request on to a server in a process known as SSL termination. However, this approach can expose the traffic between the load balancer and server to potential attack. To prevent this, you can set the load balancer to send the encrypted request on to the server instead of decrypting it first. This so-called SSL pass-through poses a potential performance issue but can be ideal if you require extra security. 

In case of a distributed denial-of-service (DDoS) attack, load balancers can also shift the DDoS traffic to a cloud provider, easing the impact of the attack on your infrastructure.  

To ensure high availability load balancing, you should at least have another load balancer that will serve as a backup. This so-called N+1 model is the least costly high availability load balancing model. 

Active-Active and Active-Passive are the other high availability load balancing models. In Active-Active, two or more load balancers operate at the same time. In Active-Standby, each load balancer has an assigned backup that will take over its load in case it goes down. 

How do Load Balancers Distribute the Load? 

To distribute workloads, load balancers rely on any of the following algorithms: 

The algorithm you select will ultimately depend on your requirements. 

Key Benefits of High Availability Load Balancing

Load balancers serve to distribute network traffic and application workloads across several servers so that not one is overwhelmed. The high availability, or continuous operation, of your IT infrastructure is achieved through this redundant system.

Ideally, this switch over from a failing piece of equipment to the other one should occur seamlessly so that users do not encounter any downtime. In the real world, minimal downtime is the more achievable objective.

Highly available load balancers serve to protect your organization from Distributed Denial of Service (DDOS) attacks through SYN cookies and delayed binding. They also conduct regular health checks to ensure that your applications and servers can still handle the volume of transaction requests. When they detect impending failure, they reroute traffic to application copies and backup servers.

In the case of web servers, highly available load balancers can separate TLS requests from the main HTTPS requests and speed up web server responses in the process.

Hardware load balancers 

Hardware load balancers consist of physical hardware, such as an appliance. These direct traffic to servers based on criteria like the number of existing connections to a server, processor utilization, and server performance. These come with their firmware that requires maintenance and software updates 

Hardware load balancers offer better performance and control with a fuller range of featureslike Kerberos authentication and Secure Sockets Layer (SSL) hardware acceleration—but require some level of proficiency for management and maintenance. Due to being hardware-based, these load balancers are not very flexible and scalable, so there is a tendency to over-provision hardware load balancers. 

Software load balancers 

Software load balancers are more straightforward to deploy than hardware versions. They are also more cost-effective and flexible and used in conjunction with software development environments. The software approach provides you the flexibility of configuring the load balancer to your environment’s specific needs. Compared to hardware versions, which offer more of a closed-box approach, software balancers grant you more liberty when it comes to changes and upgrades. 

Software load balancers can come as prepackaged virtual machines (VMs) to spare you some of the configurations but may not offer all of the features available with hardware versions. 

Software load balancers are available as standalone solutions that require configuration and management or as a cloud service—known as Load Balancer as a Service (LBaaS). Choosing the cloud service frees you from the maintenance, management, and upgrading of the locally installed server. The cloud provider handles these tasks. 

How Parallels RAS helps with high availability load balancing 

Parallels® Remote Application Server (RAS) offers you a two-point load balancing to ensure high availability. The first point of contact is an external high availability load balancer (HALB) appliance, which is a standalone VM deployed in UNIX. This is responsible for load balancing the traffic between the gateways before the actual connection. 

The second point of contact is configurable from inside the Parallels RAS Console and is about the traffic after connecting through the gateways. There are two methods: round-robin and resource-based load balancing mechanisms. 

Both HALB points are included in the standard license and require minimum effort to set up. The integrated load balancing is automatically enabled by default. 

Download the Parallels RAS trial and experience the benefits of high availability load balancing. 


IBM | https://www.ibm.com/cloud/learn/load-balancing 

NGINX | https://www.nginx.com/resources/glossary/load-balancing/ 

Digital Ocen | https://www.digitalocean.com/community/tutorials/what-is-high-availability 

Wikipedia | https://en.wikipedia.org/wiki/Load_balancing_(computing) 

HAProxy | https://www.haproxy.com/de/loesungen/high-availability/ 

Parallels | https://www.parallels.com/products/ras/capabilities/load-balancing/