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CDNs vs ADCs: What are the differences?

Dave Blakey
September 30, 2018 at 9:00 AM

Content Delivery Networks (CDNs) and Application Delivery Controllers (ADCs) have many similarities, and many differences. We are often asked about various CDNs and how they work with or compete with the Snapt ADC, and we'll try to discuss the primary differences between a service like Cloudflare and one like Snapt.

Location, location, location

The first and most critical difference between these platforms is their location. A CDN wants to be as close to your end user as possible, while an ADC wants to be as close to your servers as possible.

This is because of a fundamental difference in design. The CDN wants to move content to the edge, and the ADC wants to protect, optimize and accelerate the servers themselves.

Because of this, they work very well together. Your on site ADC has far more advanced and detailed load balancing, metrics, monitoring and acceleration while your CDN uses those optimized objects and correct headers to cache the content at the edge.



Load balancing and high availability

CDNs often include a basic load balancer which is actually great for  doing co-location load balancing, as they exist outside of your data centers.

ADCs are normally full Layer 7  load balancers, and are ideal for on-premises redundancy. They very tightly monitors your servers as only an on-premises solution can, ensuring fast response times and detailed monitoring and visibility of server health.  

Web content acceleration

With Acceleration there are components the ADC can fulfill and components the CDN fulfills. Often, both will offer web acceleration - rewriting and optimizing the content of the page.

ADCs are often able to do this more aggressively, however, with all things being equal you would want the ADC performing web acceleration as it reduces the time to get the content to the CDN in the first place. They also allow additional customization and tweaking.

The CDN fulfills the critical role of keeping that optimized content near the user. So a CDN will serve European users from Europe, regardless of where your servers are.

Security and DoS protection

No on-premises ADC can truly prevent a DDoS attack! For this you need a powerful CDN. What ADCs do provide is on-premises SSL and WAF security, as well as application specific DoS attack prevention.

It is important to have both requirements met, and this is where a CDN shines. They provide a large amount of security, and they often provide DDoS protection completely free.

Why can ADCs not prevent distributed denial of service? They are within your infrastructure. So if you have a 10Gbe link and are getting 100Gbe of traffic, even if Snapt mitigated the attack your pipe is full!

ADCs do provide DoS protection though against more focused attacks against your website. For example, Slowloris, or a port exhaustion attack.


While CDNs perform well in security, visibility is where an ADC can truly shine!

Detailed, in-depth and live monitoring of performance, stats and metrics is simply something that CDNs cannot provide. For ultimate visibility and alerts you need an ADC.

Let's give you a real world example. After a recent system update, Snapt notified us that one of our web servers was responding 500ms slower than the rest on average, via our Slack channel.

We can login and live view the traffic, response codes, which urls are slow and more.


In summary, ADCs and CDNs are complementary services - not competing ones!

Get a full, free trial of Snapt and test it today!

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