We are facing an issue where the first API call in our React Native app takes 45-60 seconds due to a slow SSL handshake. After the initial request, subsequent API calls work fine.

Our setup is as follows:

• Backend: Tomcat (Serving APIs)
• Reverse Proxy: Nginx (Handles SSL termination)
• Mobile App: React Native (Using Redux Toolkit Query for API calls)
• SSL Certificate: Let's Encrypt (Installed on Nginx)

Issue:

Whenever a user opens the app for the first time, the initial API request triggers an SSL handshake delay of 45-60 seconds. This happens only on the first request, and subsequent requests are fast.

What We Have Tried:

• Enabled SSL Session Resumption in Nginx (ssl_session_cache)

  ssl_session_cache shared:SSL:50m;
  ssl_session_timeout 4h;
  ssl_session_tickets on;
  keepalive_timeout 75s;
  keepalive_requests 100;
  

  Result: No major improvement.

• Preloaded API Calls in React Native (useEffect)

  useEffect(() => {
    triggerGetData();  // Preload API call to warm up SSL connection
  }, []);
  

  Result: Helped slightly, but still slow for first-time users.

• Enabled HTTP/2 in Nginx

  listen 443 ssl http2;
  

  Result: No noticeable improvement.

• Checked SSL Handshake Timing Using OpenSSL

  openssl s_client -connect yourdomain:443 -showcerts -time
  

  Result: Handshake took ~15 sec on first request but was fast on retries.`