当在浏览器键入URL，会发生什么？（英文版）

When we type the url in the browser and hit enter, the OS will send a packet to DNS server which will translate host names to IPs and vice versa. If we click a link on a website, there is a cache to store the IP address so the OS doesn’t have to send the same DNS request again. Both OS and browser have a cache. Time to Live (TTL) values associated with an answer from a DNS server, 5 minutes, 1 hour, or 1 day.

follow up: please tell me what cookies is and the negative side:
Cookies: can store the address of the server so the next the user visit the website, he goes to the same back-end server. Downside: the private IP of the back-end server may change; the private IP is now visible to the whole world.

有一个怪异的情况要注意一下：
If the backend is PHP based and the session in PHP is broken. And if you were on Server 1, then by chance you are sent to Server 2 by a round-robin, you might have to log in again. Or think about shopping cart.