Recently, there are always people in the group complaining, said on the high defense CDN after the site slow as a snail, the user experience directly through the heart of the earth. I look at the situation on the happy - this problem I stepped on the pit five years ago, I did not expect that now there are so many people head into it. High-defense CDN is essentially a “bodyguard”, but if you let the bodyguard stand in the wrong position, he can not only block the bullets, but also blocked all the customers outside the door.
To be honest, the high latency of this pot really can not all let the CDN back. I found that eighty percent of the cases is a configuration problem, two percent of the nodes are chosen to be bad. Last year to help an e-commerce station to do migration, the original use of a large high-defense CDN, latency soared to 300ms +, the user complaints than the order is more. Later an operation pressed to 80ms or less, the conversion rate directly back to 15%. Today I will put the bottom of the optimization skills out of the pressure box, do not just collect, remember to try.
Uncover the culprit first: what is the nature of the delayed high?
Many people see the high latency on the curse CDN vendors, in fact, the probability is that you yourself did not match understand. High-defense CDN in order to carry the attack, the traffic has to be filtered around the cleaning center, and then back to the source to the server. More than one jump, the delay naturally go up. But the key is - the location of the cleaning center, back to the source strategy, protocol selection, all can do something.
The most outrageous case I've seen is when a company used a US node to accelerate domestic users and complained about lag. Brother, this is no longer a latency problem, is the geography class did not pass ah. In addition, the TLS handshake, TCP window size, cache hit rate of these underlying details, is really the hand that strangles the neck of the delay.
Tip 1: Intelligent node selection, don't trust vendors“ ”automatic optimization".”
CDN vendors like to brag about their intelligent scheduling, but don't believe it. Their so-called “optimal node” may be the lowest cost, not the fastest. When I used CDN5 before, I found that it always dispatched users to the low load of the cold nodes, and the latency directly doubled.
Then I forced my way in and did two things: first, I used a self-built probe to monitor node latency in real time. Write a script to run ping and traceroute regularly, and pull the data into your own database to analyze. Second, according to the user's geographic area and operator to do fine-tuned scheduling. Telecom users should not be thrown into the Unicom node, Guangdong users hard to Beijing node is purely looking for scolding.
Here's the node detection script I'm using (Python version):
If you run for a week, you will be able to draw a heat map of latency, and it will be clear which node is stable and which node is floating. Then do something at the DNS level, using DNSPod or Cloudflare's intelligent resolution, according to different carriers and provinces to return to different node IPs. the actual test of this set of operations can make the delay down 40%, more than the vendors boast of the “intelligent scheduling” ten times more useful.
Tip 2: Protocol Optimization to Hold TCP/TLS Down to Earth
HTTP/2 and HTTP/3 are the true laws of flavor. Last year I was optimizing for an 08Host customer and found they were still using HTTP/1.1, with new connections being built for each resource and the TLS handshake taking most of the time. After forcing an HTTP/2 upgrade, multiplexing directly cut the load time in half.
But even more ruthless is HTTP/3 (based on QUIC). This protocol is inherently resistant to packet loss, especially suitable for mobile network fluctuations in the scene. cdn07 has been fully supported, after opening the delay fluctuations can be reduced by 30%. However, note that the old equipment may be compatibility pull crotch, have to do a good job of downgrading programs.
Nginx configuration example (HTTP/2 and 0-RTT TLS turned on):
In addition, the TLS handshake is an invisible killer. It is recommended to enable session resume and OCSP stapling, which can compress the handshake time from 300ms to 100ms. There was a customer who didn't believe that TLS had such a big impact, and I showed him the Wireshark packet capture comparison chart and immediately shut up.
Tip #3: Caching Strategies and Edge Computing to Beat Dynamic Requests to Static
The most stupid use of high defense CDN is the whole site back to the source. Some of my buddies even images, CSS go dynamic back to the source, not card you card who? I have seen the most fierce optimization is to transform the 60% dynamic request into edge caching.
For example, the user login status of such seemingly necessary to return to the source of the request, in fact, can be used edge computing to handle. CDN5 and CDN07 support edge KV storage, the user session cache to the node to reduce the return to the source of the round-trip. 08Host is more ruthless, directly support the edge of the running WebAssembly, can be aggregated at the node level of the API request.
The caching rules have to be keyed to death:
Don't forget to preheat the cache! Especially before the big promotion, use the script to brush the popular resources to the CDN edge node in advance. Once there was an e-commerce station did not do warm-up, after the start of the event CDN back to the source of the traffic burst the server, the whole 50% off into the 502 error page.
Branded Eggs: Latency Mastery from Three CDN Vendors
Purely subjective experience, for reference only: CDN5 Asia-Pacific node latency control thief stable, especially in Hong Kong and Singapore, an average of 80ms or less, but Europe and the United States nodes are more pulling. CDN07 HTTP/3 implementation of the most radical, mobile optimization is good, but the configuration of the background of the anti-human. 08Host cheap bowl, the domestic BGP line is good, but the ability to prevent DDoS is not as good as the first two, suitable for the attack is not frequent scenarios. Frequent scenarios.
One final note to offend: latency optimization is a constant battle, not a one-off after the match is made
Run latency mapping once a month, check cache hits weekly, and keep an eye on real-time monitoring daily. If you have the conditions, you can use the full-link APM tool, and if you don't have the conditions, you can write scripts to monitor yourself. Once I thought that the optimization was in place, the result was that a certain operator suddenly routed the wind, node latency skyrocketed. Later, I did a multi-line failover, and only then completely lay flat.
A high-defense CDN is not a silver bullet, it's a trade-off game - a game between security and latency. To get both, you have to be personally tuned. Those who count on out-of-the-box brothers, it is recommended to directly increase the money on the global ANYCAST, otherwise it is honestly according to my skills toss. Remember, the money saved from latency optimization is worth much more than the CDN bill itself.
