CDN Request Performance Optimization for iOS and Android Apps

This article presents a systematic performance‑optimization case study of CDN resource requests for the Poizon (得物) mobile application, covering both iOS and Android clients.

After deploying static assets to a CDN, the team observed lingering latency and stutter issues. By analyzing monitoring data, four main optimization directions were identified:

1. CDN deployment adjustment – analysis of regional latency revealed insufficient edge nodes in provinces such as Guangdong, Beijing, Hunan, Sichuan, Jiangsu, and Jilin. Adding edge nodes in these regions reduced average iOS latency from 429 ms to 331 ms (‑98 ms) and Android latency from 386 ms to 348 ms (‑38 ms).

2. TLS 1.3 upgrade – the SSL handshake accounted for >25 % of total latency. Switching from TLS 1.2 to TLS 1.3 cut handshake rounds from 2 RTT to 1 RTT, decreasing iOS average latency from 281 ms to 237 ms (‑44 ms) and Android from 307 ms to 269 ms (‑38 ms). SSL‑stage latency dropped from 210 ms to 137 ms on iOS and from 83 ms to 71 ms on Android.

3. OCSP Stapling enablement – moving certificate status verification to the server eliminated an extra client‑side query. After enabling OCSP Stapling, iOS connection‑only latency fell from 565 ms to 484 ms (‑81 ms) and Android from 401 ms to 360 ms (‑41 ms). SSL‑stage latency also improved slightly.

4. HTTP/2 upgrade – a portion of traffic still used HTTP/1.1, especially on a secondary Qiniu CDN. Migrating this traffic to HTTP/2 increased TCP reuse rates dramatically and reduced average latency (iOS: 248 ms → 221 ms, Android: 350 ms → 329 ms). TCP reuse rates rose from ~900 % to >5 000 % on iOS.

Implementation steps included command‑line verification of edge node distribution ( dig cdn.xxx.com ) and OCSP status ( openssl s_client -connect <IP>:443 -servername cdn.xxx.com -status ), as well as coordinated changes in the Alibaba Cloud CDN console during low‑traffic windows.

The overall result demonstrates that targeted CDN configuration, protocol upgrades, and TLS enhancements can achieve double‑digit latency reductions with modest engineering effort, while emphasizing the need for thorough regression testing and monitoring before and after production changes.