What is an Application Delivery Controller (ADC) and Why Should You Use One?

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How an ADC improves network, application and user experience.

Application Delivery Controllers (ADC)s use various techniques to distribute the traffic load between two or more servers, routers, firewalls and other networked resources to optimize resource utilization and improve website performance and application response time.

So, what is an application delivery controller?

Application Delivery Controllers are the next generation of load balancers and are typically located between the firewall/router and the web server farm. In addition to providing Layer 4 load balancing, ADCs can manage Layer 7 for content switching and also provide SSL offload and acceleration. They tend to offer more advanced features such as content redirection as well as server health monitoring. An Application Delivery Controller is also known as a Web switch, URL switch, Web content switch, content switch and Layer 7 switch.

Here is what Gartner has to say. “The application delivery controller is a key component within enterprise and Cloud data centers to improve availability, security, and performance of applications. Application delivery controllers (ADCs) provide functions that optimize delivery of enterprise applications across the network,” is how Gartner defines Application Delivery Controllers. “ADCs provide functionality for both user-to-application and application-to-application traffic, and effectively bridge the gap between the application and underlying protocols and traditional packet-based networks. This market evolved from the load balancing systems that were developed in the latter half of the 1990s to ensure the availability and scalability of websites. Enterprises use ADCs today to improve the availability, scalability, end-user performance, data center resource utilization, and security of their applications.”

Gartner is correct, but there is something missing — that an ADC is essentially the same thing as a load balancer. Let’s see how Progress Kemp explains it.

“An Application Delivery Controller (ADC), sometimes referred to as a load balancer, is a network server that takes processor intensive tasks off the web servers so they can focus on application tasks. ADC is a core component of an Application Delivery Network, which is made up from a suite of technologies deployed in concert to deliver applications efficiently over a network,” Kemp says in its Application Delivery Controller glossary entry.

Application Delivery Controllers Versus Load Balancers 

Application delivery solutions were built to address the challenges associated with website infrastructure complexity, performance, scalability and security. Application delivery solutions are quite diverse. They may be known as application delivery controllers (ADC), server load balancers (SLB), application front-end devices (AFE), application traffic managers and web front-ends, content switches and application switches. In order to avoid confusion, this paper will focus on datacenter solutions and refer to application delivery solutions as application delivery controllers. Today’s application delivery controllers actually evolved from server load balancers that were first introduced in the late 1990s.

ADCs provide the ability to direct Internet users to the best performing, most accessible servers. Should one of the servers (or applications on that server) become inaccessible due to any type of failure, the ADC will take that server or application off-line, while automatically re-routing users to other functioning servers. This process is essentially seamless to the user and critical to servicing the customer.

What Does an Application Delivery Controller Do?  

Here are some of the main functions of ADCs:

Balancing loads 

An application delivery controller is a network device that helps sites direct user traffic to remove excess load from two or more servers.


Caching stores recently retrieved data in a local storage location so that it can be served up for subsequent requests quickly without having to go to the original source. The original source is often over a network connection, so caching locally saves time and makes the network capacity available for other uses.


Data Compression reduces the amount of data that needs to be retained in order to ensure that the original information content of the data is maintained. When moving data across a network it can reduce the size of the data set that needs to be transmitted.

Offloading SSL processing  

To enhance and secure the user experience, more-advanced ADCs provide SSL offload/acceleration. SSL acceleration in the ADC enables you to offload the SSL handshake and encryption/decryption processes from the servers. This offloading dramatically increases the server’s performance, while decreasing the time and costs associated with the server’s SSL certificate management.

Benefits of an Application Delivery Controller

During the past five years, application delivery has emerged as one of the most important technologies in solving the problem of performance and accessibility for Internet-based applications.

Here are some key ADC features to leverage:

Network security 

ADCs are a first line of defense against distributed denial-of-service (DDoS) and myriad other attacks. ADCs can also offer web application firewalls, intrusion prevention and detection and other security features.

Terminate SSL tunneling attacks 

ADCs can quickly and easily stop SSL tunneling attacks. 

Data loss protection 

Top ADCs offer data loss protection (DLP) by inspecting data to see if it is malicious or in violation of company policies, and bloc or flag this data.

Server Load Balancing 

ADCs, or load balancers, got their start balancing traffic amongst servers. While this is still a fundamental function, ADCs have moved well beyond to address cloud, web, security and application-specific traffic.

Secure application delivery  

Today’s ADCs provide web application firewall (WAF), IDS/IPS, Zero-Trust architectures, authentication proxying, content switching, intelligent load balancing and application health-checking.  

Manage application behavior 

By understanding application traffic flows and optimizing their routing, ADCs manage and optimize application behavior.

Efficiently manage traffic flows or traffic optimizations 

By using various load balancing algorithms, an ADC can distribute users to servers that offer the best possible performance. The ADC can dynamically interrogate key server elements such as the number of concurrent connections and CPU/memory utilization.

Web and DNS protection

By balancing DNS loads, ADCs protects both web and DNS servers and keep them running via failover.

Boost Application and Web Performance

ADCs boost app and web performance in several ways, including:

  • Content caching - stores data that is likely to be used again and is unlikely to change, rather than requiring computers to retrieve it from the source every time.
  • Data compression - reduces the amount of data crossing the link — squeezing the data into smaller packets which are then combined into a larger packet, making it faster and more efficient to send across a network.
  • Layer 7 switching - uses application-layer criteria to determine where to send a request. This provides an application delivery controller with much more granular control over forwarding decisions. 

Application Performance Helps Define Application Experience

In the 1980’s, Microsoft had a heckuva time selling Windows. It wasn’t that it didn’t look good or wasn’t easy to use. It was simply too slow. Way too slow. Despite the attraction of the visual user experience, the lag of the operating system and the applications kept users clinging to their character mode software.

Today’s software is richer and more demanding of IT resources than ever. On-premises solutions work their end points, related servers and the network to the bone. Meanwhile, Cloud and SaaS solutions require a high performance, highly available network both internally and externally through the WAN to the Cloud.

The answer is to adopt Application Delivery Controllers which optimize application delivery so your Cloud and on-premises end point and server apps run in ways that not only cause no complaints, but pleases users — just like your car engine after a tune up.

The Application Delivery Fabric

The old way of simply setting up ADCs where needed with no relation to one another no longer works. Instead, these devices should be knitted together into a fabric.

“A better way to approach load balancing in the new agile and multi-cloud world is to think of the complete application delivery infrastructure as a single fabric. Irrespective of the delivery location for an organization’s applications – data centers, private cloud, or from multiple public cloud providers, tracking of the load balancing traffic should include all locations. Choosing a load balancing solution that allows for aggregated traffic monitoring and billing over all sites means that you only pay for the capacity used across the whole organization,” the blog says.

How does all this become a fabric? Application Delivery Fabric is a framework which gives organizations a single point for control, analysis and diagnosis of key application metrics. 

Components of an application delivery fabric include:

  • Application Delivery Controller - intelligently manages client connections to complex web and enterprise applications. The controller is a software program that manages or directs the flow of data between two entities.
  • Management and Control Interface - for application delivery assets showing their status and performance. This should provide performance metrics across all hosting platforms: data center, private cloud, Infrastructure as a Service (IaaS), Platform as a Service (PaaS) and public cloud.
  • Monitoring Service - delivers insights from within the application environment, reporting anomalies and suggesting remediation that can be handled by an organization’s own IT staff or by the ADC vendor’s support team.
ADC is a core component of an Application Delivery Network, which is made up from a suite of technologies deployed in concert to deliver applications efficiently over a network.

Customers Embrace Application Delivery

We can say we like application delivery and load balancing, but the real proof comes from actual customers. On Gartner Peer Insights, LoadMaster has earned 4.9 stars (out of 5, of course!) and 90% of real customers rate it a perfect 5 stars. Here are a few examples:

Cloud-Ready Load Balancing

A transportation firm is using LoadMaster for application delivery and will rely on it as it moves to the Cloud.

"We've been using LoadMaster for a few years, already powering our marketing website. We've had a few projects deployed that needed the traffic routed to different systems depending on the user/requested resource. Our installation of Loadmaster was not only able to support the ever-growing needs for different streams, but also deliver exceptional performance. We are planning to migrate from a co-location to a full Cloud solution, and we know for sure we will be taking our LoadMaster with us for the ride."

Load Balancing Microsoft Exchange — With Ease

LoadMaster is not new to load balancing Microsoft Exchange. In fact, back in 2013, Redmond Magazine named LoadMaster its Third-Party All Star for Exchange load balancing. Years later, customers continue to achieve success load balancing Exchange with LoadMaster. One customer used an HA pair of LoadMaster X3 hardware appliances to load balance Exchange 2016 at a remote site. Here’s what they had to say about the experience.

“Installation and configuration was easy and any issues that arose were handled quickly by support. My sales team was responsive during the purchase. We use another load balancer in our main office which is much more complex to configure. So far, I am very satisfied with the [LoadMaster] product selection.”

Another customer, this one in higher education, shared this experience using LoadMaster for its application delivery, including running Exchange for 10,000+ students.

“We did not have a load balancer before LoadMaster, and we needed one to increase security and performance. For someone like me, who cannot be an expert in all areas, it is nice to have Kemp’s support in your back pocket. They provide expert help fast to help me with my most complicated load balancing needs. It is very powerful. We run more than 100 services — including Exchange for 10,000 students — and the LoadMaster is never busy. It almost looked bored… I like the raw power and performance LoadMaster provides, plus the perfect reliability. We have used LoadMaster for five years and it has never failed.”

The ADC Future is Here

The leading ADC on the market today, LoadMaster offers affordable load balancers available as virtual, software,and hardware-based. You won’t find a more flexible or capable option from any other vendor.

With more than 100,000 deployments, LoadMaster offers the most capable solutions for load balancing to ensure applications are secure, highly available and running at peak performance. Talk with a technical expert to learn more.

Learn More

Learn all you need to know about ADCs and how your enterprise can benefit on Kemp’s Application Delivery Controllers page.


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Doug Barney

Doug Barney was the founding editor of Redmond Magazine, Redmond Channel Partner, Redmond Developer News and Virtualization Review. Doug has also served as Executive Editor of Network World, Editor in Chief of AmigaWorld and Editor in Chief of Network Computing.