What happens after entering an URL

In general, there are following steps.

  1. TCP connection
  2. HTTP transaction
  3. TCP disconnection

enter_url

In details,

  1. Browser gets the IP address and port from URL.

    DNS not only returns the server's IP address, but also the CDN's address where the static files are cached.

  2. Browser establishs TCP connection by 3-ways handshake.

  3. Browser sends http requests to the server.

  4. Server receives the requests and sends the responses back.

    1. Once the server receive the requests. It will sends them the correct machine if a website has several machines.
    2. The host machine will first check the cache, such as Redis (memory-level), Varnish (disk-level). If the cache is found, return it.
    3. If the cache isn't found, the web application, such as Django, Tomcat, etc, takes cares of the requests. It may visit the database to get some data.
    4. The responses are sended back, and the caches in CDN are updated, too

  5. Browser diconnects the server by 4-ways handshake.

  6. Browser renders the responses.