Shulou(Shulou.com)06/03 Report--

Type the URL, press enter, what happened?

Step 1: the browser gets the IP address and port number of the server from the input in the address bar

If you type a domain name, you must first resolve the domain name to the server's IP address.

The parsing process is as follows, and there is a multi-level cache in the parsing process:

Browsers first check whether their own cache exists-- > if not, then check the operating system cache-- > if not, local Host files-- > wild DNS servers (including local DNS), root DNS, top-level DNS, authoritative DNS

Note:

It is possible for DNS parsing to give the IP address of the CDN server, and then CDN returns static resources directly without requesting the origin server.

Step 2: the browser uses TCP's three-way handshake to establish a connection with the server

Step 3: the browser sends the assembled message to the server

Step 4: after receiving the message, the server processes the request, and then sends the message to the browser.

Step 5: the browser parses the message and renders the output page

Step 6: because of the long connection feature of HTTP, the connection will not be closed immediately by default, so there will not be four waves for the time being.

This picture comes from the network.

CDN caches static resources, and for dynamic resources, it can only be obtained from the target website.

Request reaches the load balancer server (such as Nginx)

The load balancer device will first access the cache server in the system.

There are usually memory level cache Redis and disk level cache Varnish

They function like CDN, except that they work in an internal network

Cache the most frequently accessed data for a few seconds or minutes to reduce the pressure on the back-end application server.

If it is not in the cache server, the load balancing device will forward the request to the application server.

For example, the Django of Java's Tomcat,Python, and then access the later database service.

The result of the execution is then returned to the load balancer device, and a copy may also be put in the cache server.

The source and network of the following figure

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