How Much Can CDN Acceleration Boost Download Speed? A Real‑World Test on Tencent and Alibaba Cloud

Test Objective

Evaluate whether a CDN can compensate for low outbound bandwidth (1 Mb/s on Tencent Cloud, 5 Mb/s on Alibaba Cloud) when downloading large files.

CDN Overview

A Content Delivery Network caches origin content at geographically distributed edge nodes. By adding a CNAME record that points to the CDN domain, DNS resolution directs user requests to the nearest edge node, which serves the cached file directly, reducing latency and increasing available bandwidth.

Test Environment – Tencent Cloud

Provision a Tencent Cloud VM with a 1 Mb/s outbound limit and install the Baota panel.

Upload Moba.zip and make it available at http://tl.guotiejun.com/Moba.zip.

Measure raw HTTP download speed using a browser, Thunder, and FTP. Observed speed ~125 KB/s, fully utilizing the 1 Mb/s link.

Create a CDN domain in the Tencent Cloud console; the system generated the CNAME www.test.com.cdn.dnsv1.com.

Configure the domain’s DNS (e.g., at Wanwang) to resolve to the CDN CNAME.

Trigger cache pre‑warming via the CDN console.

Results – Tencent Cloud

After CDN activation and cache pre‑warming, peak download bandwidth reached approximately 10 Mb/s (limited by the test file size) and average speed stabilized around 1.5 MB/s. The CDN hit rate was 53.63 % and total CDN traffic consumption was 0.97 GB.

Test Environment – Alibaba Cloud

Create an Alibaba Cloud VM with a 5 Mb/s outbound limit.

Place a 209 MB file ( software.zip) in the web root and map the domain cdn.guotiejun.com to the VM’s IP address.

Download the file directly (no CDN) and record a stable speed of ~660 KB/s, matching the 5 Mb/s bandwidth ceiling.

Add the same domain to Tencent Cloud CDN, obtaining the CNAME cdn.guotiejun.com.cdn.dnsv1.com, and enable cache pre‑warming.

Observations

When an edge node already has the requested file cached, download speeds can exceed 10 MB/s.

If the edge node lacks the file, the first request incurs a cache miss and pulls the data from the origin; subsequent requests benefit from the cached copy.

Cache entries are evicted after a few hours of inactivity, causing speeds to revert to origin levels.

Regional performance varies: a Beijing Mobile edge node saturated at 1.17 MB/s, while other regions showed lower speeds, illustrating the impact of proximity to the edge node.

Key Metrics

Raw VM download (no CDN): 125 KB/s (Tencent) and 660 KB/s (Alibaba).

CDN‑accelerated download (cached): up to 10 Mb/s peak, average 1.5 MB/s (Tencent); later tests on Alibaba showed peaks up to 28 Mb/s.

CDN hit rate: 53.63 % (Tencent) and 41 hits recorded for the Alibaba test.

CDN traffic usage: 0.97 GB (Tencent) and 158 MB (Alibaba).

Conclusion

CDN acceleration yields significant speed improvements for large files when the content is accessed frequently enough for edge nodes to retain the cache. In low‑traffic scenarios (≈20 requests per day), cache eviction occurs quickly, and the CDN does not provide a cost‑effective performance gain. Achieving the expected benefits requires correct domain CNAME configuration, cache pre‑warming, and an understanding of the CDN’s caching policies.