If you have already purchased the COS (Cloud Object Storage) external network downstream traffic package, whether you need to purchase the CDN (Content Delivery Network) back - to - origin traffic package depends on your specific usage scenario.
The COS external network downstream traffic package is mainly used to cover the traffic when users directly download objects from your COS storage. For example, if you have a large number of images stored in COS and users frequently access these images through direct URLs, the external network downstream traffic package can help you save costs on this type of access.
On the other hand, the CDN back - to - origin traffic package is for the traffic generated when the CDN nodes fetch content from your origin server (in this case, COS). When the CDN nodes do not have the requested content in their cache, they will retrieve it from your COS. For instance, if you have a dynamic website with frequently updated content, and users request this content through the CDN, and the CDN nodes need to fetch the latest content from COS, then CDN back - to - origin traffic will be generated.
If your users mainly access the content directly from COS and the CDN is only used for caching static content that rarely needs to be refreshed from the origin, you may not need the CDN back - to - origin traffic package. However, if your application has a high rate of cache misses on the CDN and frequently fetches data from COS, purchasing the CDN back - to - origin traffic package can help you manage costs more effectively.
In the context of cloud services, if you are using Tencent Cloud's COS and CDN services, Tencent Cloud provides detailed traffic statistics and analysis tools in its console. You can use these tools to monitor your traffic usage and make informed decisions about whether to purchase additional traffic packages. Additionally, Tencent Cloud's CDN service offers features such as intelligent caching and origin - pull optimization, which can help you reduce back - to - origin traffic and improve the performance of your application.