What are the common problems of CDN return to the source? Full summary of CDN return to the source solutions

in the full link of CDN acceleration, the return to the source is the core link connecting the edge node and the source station. Once there is a problem, it will not only lead to cache failure and slow content loading, but also directly cause the risk of source station pressure overload and service interruption. In daily work, many operation and maintenance personnel often lack control over the details of CDN return to the source, and it is difficult to quickly locate the root cause when encountering problems. This paper will systematically sort out the common problems of CDN return to the source, and give targeted solutions in combination with actual scenarios to help practitioners optimize the CDN return to the source link and improve the stability of service distribution.

What are the common abnormal problems of CDN return?

CDN return to the source is usually directly reflected in the content access experience of the user, and it will also be reflected in the monitoring data of the source station.

1, the failure to return to the source causes the content to fail to load

such problems are mostly manifested as 4xx or 5xx error codes when users access content. The core incentives include source server downtime, firewall interception of CDN node IP, and failure to return to the source domain name resolution. For example, some enterprise source stations will set up IP whitelists in order to ensure security, but do not include all return node IPs of CDN manufacturers, which will lead to node requests being intercepted and trigger CDN return failure.

2, the source frequency is too high to cause the source station overload

when the CDN return frequency far exceeds the source station bearer threshold, it will cause the source station CPU, bandwidth occupancy soaring, and even cause service collapse. The common reason is that the cache configuration is unreasonable, such as the cache expiration time is set too short, or the static resources are not set cache rules, resulting in frequent requests from edge nodes to the source station and continuous consumption of source station resources.

3, inconsistent return source content causes cache confusion

users access the same content, different regions or different nodes to return the content there are differences, mostly because of the CDN back to the source of the cache key rules set improperly, or the source station content update did not trigger cache refresh in time, resulting in some nodes still retain the old version of the content, the old and new content alternately cause user confusion.

What are the common configuration errors of CDN back to the source?

many CDN return problems are not due to hardware failures, but the details of the configuration link omission, these errors are easy to be ignored but will cause persistent link anomalies.

1, the return protocol does not match the source station

part of the operation and maintenance personnel in the configuration of CDN back to the source, the source station is not synchronized protocol type, such as the source station only supports HTTPS protocol, but the CDN back to the source is set to HTTP, will lead to the request is rejected by the source station; conversely, if the source station does not configure HTTPS certificate, CDN back to the source forced to use HTTPS, will also trigger SSL handshake failure, triggering back to the source exception.

2, back to the source Host header setting error

Host header is the domain name information carried by the CDN node when requesting from the source station. Some source stations distinguish different service sites based on the Host header. If the Host header setting of the CDN back to the source does not match the expectations of the source station, the source station will not be able to correctly identify the service corresponding to the request. Return wrong content or directly reject the request. For example, some enterprises use the same server to host multiple websites, and rely on the Host header to route the request. The CDN back to the source Host header error will directly lead to information delivery errors.

III. Targeted solutions to the CDN return problem

in view of the common problems and configuration errors of the above CDN return source, combined with the actual operation and maintenance experience, the practical solution and optimization scheme are given.

1, quick troubleshooting and repair of return failure

first through the CDN vendor monitoring platform to view the source error code, if 403 error, priority check the source station firewall or whitelist configuration, timely return to the source node IP segment provided by the CDN vendor all added to the whitelist; if 502 or 504 error, you need to check the source server status, troubleshooting whether there is a downtime, port is not normal listening and other issues, while verifying the DNS resolution of the source domain name is normal.

2, the optimization scheme with high return frequency

core is to optimize the cache strategy, set differentiated cache expiration time for different types of content, such as static pictures, videos, etc. can be set for a long cache period, while dynamic pages or frequently updated content can be set for a short period, and at the same time turn on the CDN's intelligent cache refresh function, actively push refresh instructions when the content of the source station is updated, to avoid nodes frequently initiating invalid CDN return requests. In addition, the CDN return merge function can also be turned on, merging multiple identical return requests in the same time period into one to reduce the amount of source station requests.

3, back to the source content inconsistent correction method

first unified CDN back to the source of the cache key rules, to avoid the request parameters, cookies and other differences resulting in the same content to generate multiple copies of the cache; secondly, after the source site content update, timely refresh interface through the CDN manufacturer's console call, the corresponding resource cache forcibly refresh; at the same time open the CDN back to the source verification function, so that the node before the cache expires to check whether the content is updated to the source station, only when the content changes CDN back to the source request to ensure that the cache content consistent with the source station.

To sum up, CDN return is the core link to ensure the acceleration effect of CDN, and its abnormal problems are mostly caused by configuration omissions, unreasonable cache policies or conflicting source station security rules. By sorting out common return failure, high frequency, inconsistent content and other problems, combined with whitelist configuration, cache strategy optimization, return parameter calibration and other schemes, it can effectively improve the stability of CDN return link, reduce source station pressure, and provide users with a smoother content access experience.