How HTTP client-server interaction works:
A Web server receives a request from a client for index.php page, for example, generates a page with static HTML content and sends to the client. This is Time to First byte (TTFB).
Then client web browser starts executing index.php: requests content mentioned in the page – various scripts, images etc. The scripts are delivered from the server and web browser starts executing them.
Possible causes
- Slow DNS servers are used or dns servers reachability issues.
- Server-side problems: web or MySQL service workload/bad optimisation.
- Network problems: connection is not stable or bandwidth is not sufficient.
- Site uses not optimal PHP version
- Website code problems: content size and website code optimization.
