Recently, several operation and maintenance brothers complained to me, said on the high defense CDN site acceleration effect is not obvious, sometimes even slower than the direct connection. I went up to take a look at the configuration on the music - where is this acceleration ah, simply in the source station to add blockage.
The case of an e-commerce station is particularly typical: they spent a lot of money to buy a well-known high-defense CDN, but the dynamic interface and static resources mixed with the same set of caching strategies. As a result, when users visit the home page, the product images are cached, but the price inventory information each time to go back to the source to get, the page load time is actually 4.2 seconds.
In fact, the problem lies in the caching rules. Many teams think that turning on the CDN is all right, but ignore the most critical business scenarios to adapt. I found that the reasonable configuration of the CDN can make the first screen loading time from 3 seconds + down to 800 milliseconds, and this only need to do three things: motion separation, cache layering, edge computing.
First of all, the basic operation of static and dynamic separation. Don't believe those ”one-click optimization” propaganda, I've seen too many sites throw API interfaces and static resources into the same caching policy:
This configuration is a disaster for dynamic interfaces. The user submits an order and sees inventory data from ten minutes ago, so it's a wonder they don't place an order. The correct approach should be to hierarchize the processing based on business characteristics:
The second layer of optimization is the cache layering strategy. cdn5, the vendor, did a smart job by allowing the setting of differentiated caching strategies for edge nodes and middle tier nodes. For example, when a user requests for the first time, the edge node obtains resources from the middle layer and caches them for two hours, while the middle layer caches them for 24 hours. This not only ensures the acceleration effect of hot content, but also avoids excessive storage pressure on the edge nodes.
The measured data is very illustrative: after enabling layered caching on an information website, the source station traffic dropped from a daily average of 3.2TB to 400GB, and the 95% request was responded to at the edge node. Special attention should be paid to the video business, CDN07 provides a slice caching function that can cut large files into 2MB blocks and cache them separately, so that the user experience is much smoother when dragging and dropping the progress bar.
Edge computing is where the technology gap really manifests itself.08Host plays this aspect the most, allowing custom logic to run on the CDN node. For example, we can recognize the type of device according to User-Agent, return WebP format images for mobile and AVIF format for desktop:
Caching strategies for security are often overlooked. Some teams directly cache error pages to save time, causing users to see cached 500 error messages. The correct approach is to differentiate status codes by caching keys:
These days even CDNs have to ”prevent teammates”. In one emergency response, we found that the attacker intentionally requested a large number of resources with different URL parameters to exhaust the cache capacity. Later, we added a parameter whitelist to the cache key to keep only the necessary query parameters:
The warm-up mechanism is a hidden trick to enhance the experience. Especially for e-commerce promotion scenarios, pushing the event page to the edge node in advance can avoid traffic flooding.CDN5's API interface works well, just call it:
A final word on monitoring metrics. Don't ever just look at the vanity metric of hits, I'm more concerned with theByte Hit Rate和Flow rate saving ratioIt's a good idea. A customer once bragged about 80% cache hit rate, in fact, because large files are not cached, the traffic saving ratio is only 35%, this pseudo-optimization is really pitiful.
A truly professional configuration should be like Chinese medicine, customized according to business characteristics. Information business focuses on long caching cycles, e-commerce platforms need to refine the dynamic cache, video station to optimize Range Request support. I remember when I debugged the CDN for a live broadcast platform, by adjusting the size of the slice cache, I was able to reduce the lag rate from 1.2% to 0.3%.
Now look back at the beginning of the e-commerce case, we finally gave the program is: static resource caching for 30 days, product detail page caching 5 minutes, price interface caching 10 seconds and add a soft clearing mechanism. After the transformation of the page load time down to 1.1 seconds, the quarterly bandwidth cost savings of more than six hundred thousand.
The thing about technology is that people are afraid of what they think. Don't look at the vendor's documentation to say a lot of things, what suits you is the best. After each configuration of caching rules, I will use curl to test the response header of different edge nodes to confirm that the Cache-Control and Age fields meet the expectations. After all, if you have been in this business for a long time, you know that the devil is hidden in the response header.
