HTTP Request Timeline

By: Dusty Arlia
Published on Tuesday, September 15, 2015 at 9:56 PM
Last Updated on Monday, September 28, 2015 at 7:57 PM
Total Updates: 2

Server: server powers on
Server: performs POST
Server: web server starts
Client: The application calls a function to look up the IP address behind a hostname. This function is in the system's shared library, so the application doesn't need to know the details of how it works or whether the implementation will change.
Client: When the function in the shared library runs, it acts according to a set of rules (found in /etc/nsswitch.conf on Linux machines) to determine a plan of action on lookups (e.g. the rules usually say that even before going to DNS, check for a manual override in the /etc/hosts file)
Client: When the function decides to use DNS for the name lookup, it consults an additional configuration file to find a DNS name server. The name server is given as an IP address.
Client: The function sends a DNS lookup request (over the network) to the name server
Client: The name server replies with the IP address for the hostname, and the function returns this IP address to the application
Client: Client establishes a TCP connection to the web server, typically on port 80
Client: HTTP request sent
Server: HTTP request received
Server: response sent
Client: HTTP response received
Client: possibly renders received file in web browser

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