At one point or another, we have all been there: staring at the spinning wheel, watching the page you just painstakingly designed load, wondering where on Earth your users have gone. Or even worse: you are about to hit the send button for that all-important email to your boss, announcing how you managed to convince the CFO that you are ready for a new CDN to serve website assets and improve performance (because if your marketing team is like ours, they have gone CDN crazy and convinced you that every site needs a CDN).
You click send, only to be haunted later by a support ticket that reveals that your CDN provider isn't as low-latency as they promised (during that rainbows and unicorns sales pitch).
CDNs serve your website assets and files from locations physically closer to your end-users (via Points of Presence or PoPs). By doing this, they deliver that content faster from a location closer to the users, reducing latency, load times, and overall providing a more seamless experience for users and end-consumers of that content.
The problem is that not all CDN providers are created equal, and in some cases, the difference in performance between providers can be considerable.
A one-second delay in page response time has been shown to decrease conversion rates by 7%. When you translate those conversions to money coming into your business, this difference between good and poor CDN performance can directly and drastically affect your bottom line.
If the slow CDN response times are drastically increasing your bounce rates, this can also have a huge impact on SEO results. This is because Google Core Web Vitals, which are now a ranking factor, directly impact a user's experience of your website (hence, affecting your rankings in the search results).
So, while the business case is a major reason to care about CDN performance, there are also important technical considerations to consider, such as network and server latency, round-trip time, and cache hit ratio, to name a few.
Latency and Response Time: CDN performance will vary by network so measuring and monitoring round trip times and response times are both crucial in ensuring optimal performance.
Connect Time: Time it takes to establish the connection
Round-Trip Time (RTT): Total time for a request to go from client to server and back.
Time To First Byte (TTFB): How long does it take the CDN to respond to the request
Cache Hit Ratio: Content that is not in the CDN's cache will need to make a roundtrip to the origin server to fetch the required content. A higher cache hit ratio means faster content delivery and lower origin server requests.
Bandwidth and Throughput: CDN providers have maximum amounts of data transfer they can handle over their networks per second. The more data your website needs to transfer, the more throughput (bandwidth) you need to support that amount of traffic.
Load Balancing: Look for CDNs that balance loads between servers based on utilization. They can also provide load balancing that distributes the content delivery load geographically.
Global Coverage: Check to make sure the CDN provider you choose has adequate Points of Presence (PoPs) globally and in your key target markets. A good rule of thumb to ensure the best performance is that the CDN has Points of Presence within 300 miles or less of the majority of your visitors.
Performance Variations by Region: CDN performance isn't always equal globally, with some CDNs offering great performance in North America and Europe but struggling in other key growth markets like South America and Southeast Asia, as your business expands globally. You want a CDN provider that performs well no matter where your customers are located.
Dynamic Content Delivery: Most CDNs are great at serving up static files like images and CSS, but when it comes to dynamic content that is changing on a per-user basis or not available in the CDN's cache, the performance can vary. Ensure your CDN provider has good options to accelerate the delivery of dynamic content.
When it comes to CDN provider performance, it is helpful to first take a look at the major vendors that dominate the market to get a sense of performance capabilities and limitations.
Strengths: Great global coverage, integrated security features, and competitive pricing make Cloudflare a solid option for many businesses.
Potential weaknesses: While their performance is good, they can be slower for very dynamic content and have fewer advanced features compared to some competitors.
Strengths: Largest and most widespread global CDN network with exceptional enterprise-level performance and security.
Potential weaknesses: Pricing is typically higher, and their platform can be more complex to implement and manage than other CDNs.
Strengths: Offers superior performance for dynamic content with excellent API control and real-time content purging.
Potential weaknesses: They have fewer global PoPs than competitors like Akamai, which could be a concern for some global use cases. Pricing can also be higher, especially for advanced features.
Strengths: Tightly integrated with AWS services, with good performance and pricing for AWS users.
Potential weaknesses: May not be as feature-rich as some of the other specialized CDN providers, with less advanced caching and optimization options.
Strengths: Offers simple pricing and has a good performance-to-cost ratio, with relatively easy implementation.
Potential weaknesses: Smaller network and less global coverage compared to larger CDN providers. Fewer advanced features than some competitors.
It's important to implement monitoring strategies to determine the performance differences between CDN providers, as well as to monitor that performance once you've settled on a particular provider.
Synthetic Testing: Synthetic monitoring involves using scripted tests from multiple locations to simulate user interactions with your content delivery network (CDN). It can provide consistent benchmarks to use as a baseline for comparing performance over time or between different CDNs.
Real User Monitoring (RUM): RUM collects performance data from real users as they interact with your website or application. This can be an effective way to gain insight into how your CDN is performing in the real world across various devices, browsers, and network conditions. Many CDN providers offer RUM tools, or you can implement third-party solutions.
Basic HTTP Monitoring: A simpler approach to CDN monitoring is to perform basic HTTP monitoring to track response times and availability for key assets that are being delivered via your CDN.
When measuring CDN performance, some of the key metrics you should be tracking include:
Monitoring these performance metrics over time can help you identify trends and patterns that can inform your CDN optimization and selection strategies. In addition to these, you'll want to implement performance monitoring for your business-critical applications using synthetic and real user monitoring to track performance by device, location, browser, and connection type.
In addition to selecting a CDN provider with good performance in the key regions where your users are located, there are several optimization strategies you can use to improve CDN performance.
Implementing a multi-CDN approach can be an effective way to optimize CDN performance and ensure that you are always routing traffic to the best-performing CDN for the job. In this approach, you strategically use multiple CDN providers, selecting which traffic to send to each one.
Common use cases for this include:
Implementing a multi-CDN strategy can be more complex to set up and manage, but it can also provide significant performance and reliability benefits. While using more than one CDN will likely increase costs, if you are able to significantly improve the performance and experience for your users, it could also result in measurable business improvements.
CDNs are expanding their capabilities beyond simple content delivery to offer edge computing capabilities.
Edge computing allows you to:
Services such as Cloudflare Workers, Akamai EdgeWorkers, and Fastly's Compute@Edge offer these capabilities and are pushing the boundaries of traditional CDN services.
A multi-CDN strategy can have a very positive impact on performance by enabling geographic, content-based, or even real-time performance-based routing to optimize content delivery.
While a multi-CDN approach increases complexity (it requires more configuration and management to route traffic to multiple providers), the gains in performance (observed in testing to be an average of 15-30% increase in global performance metrics) and business benefits can be well worth it.
Synthetic and real user monitoring can be very effective when used together.
Synthetic testing provides consistent benchmarks that are useful for A/B testing different CDN providers and establishing baselines for ongoing performance comparisons. RUM gives insight into real-user performance (but may not provide as granular of insights, depending on the solution).
The best approach is to use both to give you visibility into your baseline CDN performance, as well as real user performance metrics to measure your end user's experience and correlate it to business metrics like conversion rates.
DDoS protection, while essential for network security, can introduce some latency as it inspects and filters traffic. The impact on performance will depend on a number of factors, including:
In testing, we have seen the performance impact range from 1-5ms to over 50ms depending on these and other factors. Striking the right balance between security and performance can be challenging, and the right level will depend on your use case.
The performance of CDN providers is an important technical and business consideration for your organization. Differences in network performance between providers can have a major impact on user experience and business results (such as conversion rates) and can directly affect your bottom line.
Selecting a CDN provider (or providers) should be an informed decision based on performance in key regions and for key use cases, rather than simply going with the cheapest option or based on marketing materials. Implementing monitoring to get objective performance data is the only way to make truly informed decisions and optimize your configuration for your unique traffic patterns and content.
Armed with that performance data, you can select the best CDN provider(s) for your needs based on their actual performance (rather than their claims). You can also optimize your configuration and routing to get the most performance for your budget and hold providers accountable to their SLAs.
Measuring and monitoring that performance can also help you provide justification and hard data to the business to support your CDN investment.
For basic CDN performance monitoring, PRTG Network Monitor offers HTTP sensors that can help you track response times and availability of your web content from your monitoring locations. This can provide useful data for overall website performance, including content served through a CDN.
Start monitoring your CDN provider performance today and download the free trial of PRTG Network Monitor.