How to troubleshoot the CDN return to the source fault? Analysis of CDN return to the source processing steps

in the service architecture of CDN acceleration, CDN return to the source is the core link connecting edge nodes and source stations. Once a failure occurs, it will directly cause users to be unable to obtain the latest resources, and even cause abnormal access to the whole site. When many operation and maintenance personnel encounter CDN return to the source failure, they often delay the repair time due to confusion in troubleshooting ideas. This paper will systematically sort out the troubleshooting logic of CDN return to the source fault, from pre-inspection to core diagnosis, to emergency repair and long-term optimization, and provide a set of practical processing guidelines for operation and maintenance personnel to help quickly locate problems and restore services.

1, CDN return source fault pre-investigation points?

in-depth diagnosis of CDN back to the source before the fault, first complete the basic pre-investigation, can quickly eliminate common simple problems, narrow the scope of the fault.

1, CDN back source configuration validity verification

first log in to the CDN management console, check whether the configuration of the return domain name, source station IP, return port, and return protocol is correct, and focus on confirming whether there are configuration changes that are not synchronized and domain name resolution errors. For example, some operation and maintenance personnel do not timely update the CDN return configuration after modifying the source station IP, which will cause the edge node to continue to initiate requests to the old IP, causing the return to fail.

2, source station basic connectivity test

through the online diagnostic tool of the CDN node, or simulate the network environment of the CDN return to the source locally, ping the source station IP and domain name, test the TCP port connectivity, and confirm whether the source station provides services normally. If the source station itself is down and the firewall intercepts the return request state, it will also directly trigger the CDN return fault.

2. CDN return source fault core diagnosis method?

completed the pre-investigation, if no basic problems are found, it is necessary to enter the core diagnosis link of CDN return fault, and dig deep into the root cause of the problem from the dimensions of request link and log information.

1, CDN return request link full link tracking

use the link tracing tool provided by the CDN service provider to view the full path of the return request from the edge node to the source station, focusing on the delay, packet loss rate and response status code of each node. For example, if the edge node in a certain area returns to the source with high latency, it may be that the network link from the area to the source station is congested; if the 403 status code is returned, it is most likely that the access rights configuration of the source station restricts the CDN return request.

2, CDN return log refined analysis

export detailed logs of CDN return to the source, including request time, return URL, source station response code, error information and other fields, and locate high-frequency fault points by filtering abnormal response codes (such as 5xx, 4xx). For example, a large number of 504 timeout errors appear in the log, indicating that the source station is too slow to process CDN return requests, and it is necessary to optimize the service processing performance of the source station; if a 404 error occurs, check whether the path back to the source URL matches the source station resource path.

three, CDN back source fault emergency repair plan?

locate the root cause of the CDN return to the source, emergency repair measures should be taken immediately, priority should be given to restoring business access, and then subsequent root cause rectification should be carried out.

1, temporary switching CDN back to the source configuration

If the source station cannot be quickly restored due to hardware failure or large-scale upgrade, the CDN can be temporarily switched back to the standby source station, or the cached safety-net strategy of the CDN node can be enabled to temporarily provide services to the static resources cached by the edge node to reduce the impact of the failure on the user.

2, emergency adjustment CDN back to the source strategy

if the fault is due to insufficient bandwidth of the source station and limited processing capacity, the frequency of CDN return to the source can be temporarily adjusted, the cache expiration time of static resources can be extended, and the frequency of CDN return to the source request can be reduced; at the same time, the CDN's intelligent return to the source limit viewership of function can be turned on.

4. CDN long-term operation and maintenance optimization strategy?

solve the current CDN return fault, it is necessary to reduce the probability of fault recurrence through long-term optimization strategies to improve the stability and efficiency of CDN return.

1, build a multi-live CDN back to the source architecture

deploy the primary and standby dual source stations and configure the intelligent return routing strategy of the CDN. When the primary source station is abnormal, the CDN node automatically switches to the standby source station to return to the source to realize automatic fault switching. At the same time, the return line can be divided according to the region, so that the edge nodes in different regions can preferentially select the nearest source station for CDN return to reduce network delay.

2, improve the CDN monitoring system

build full-dimensional monitoring of CDN return to the source, including core indicators such as return success rate, return to the source delay, and source station response time, set threshold alarms, and notify operation and maintenance personnel in time when the indicators exceed the normal range. At the same time, regularly conduct offline analysis of CDN return logs, mine potential risk points, and optimize and adjust in advance.

To sum up, CDN source troubleshooting needs to follow the logic from basic to core, from emergency to long-term, first through pre-troubleshooting to quickly eliminate simple problems, and then with the help of link tracking and log analysis to locate the root cause of the fault, and then take emergency measures to restore business, and finally through the architecture optimization and monitoring system to build a stable operation and maintenance of CDN source. This complete process can help operation and maintenance personnel to efficiently deal with all kinds of CDN source faults and ensure the continuous and stable operation of the business.