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Web server tutorial - Part 1
By Vans Information <content@vansinfo.com>
Basically for communication where there is a client-server flavor, the server process creates a socket and the client socket accesses the server through client socket techniques. Socket
A socket is fundamentally nothing but an end point of communication. It can be of two types: Physical socket and Logical socket. In Logical socket operating system has its system calls, which creates them. Now for client-server access the socket needs three things to provide service or ask for service.
Let's take few more examples then start with Web server. Web communication Web communication deals with a browser type of client process and Web server type of server process. What actually happens when a user writes http://www.yahoo.com? Well, the browser transfers the URL to current machine's operating system with a destination address' operating system, which is responsible for extracting protocol i.e. "http" from the client socket (browsers) and then it packets data using layer software and over the packet it attaches the header http. This enables the remote machine to hand over the request to Web server of remote machine. Why so? Because there can be many a server running on the same machine so the particular services are distinguished by their protocol. But how should we explain when telnet and ftp both are using same protocol but have different server Processes? The answer is that they are distinguished by their port numbers. Services may have same protocol but not the same port number. After this the operating system throws the data to network interface card through the ram and then network interface card gives it to nearest gateway, which sends the data to the server machine at server end. The network card gives a signal back to operating system that a data enclosed with http header using TCP/IP header has arrived. One's operating system checks that data has http wrapper and searches for Web server on that machine. When it finds, it hands over the data and pays attention to other processes. Before the Web server processes the data, it goes through a filtration by the gateway process implemented on the Web server, which actually filters the raw data. This concept implemented is called as common gateway interface that has the Web server environment variables, which stores the data in different variable. When the user asks for some unnecessary data, headers also get attached with data and so the need for filtration. Apache as Web server
Setup: We have to first configure the DNS. Then configure the following file (redhat 6.2) /etc/httpd/conf/httpd.conf If we use Apache as a Web server whether on Windows platform or Linux, the main file which is used is called /etc/httpd/conf/httpd.conf
The root directory of Web server is /etc/httpd, which is divided into three parts: Lets open the file /etc/httpd/conf/httpd.conf and take a detailed look at the macros to be used.
httpd.conf-Apache HTTP server configuration file This is the main Apache server configuration file. It contains the configuration directives that give the server its instructions. Note: See http://www.Apache.org/docs for detailed information about the directives. Do not simply read the instructions in here without understanding what they do. They're here as hints or reminders. If you are unsure consult the online docs.
After this (httpd.conf) file is processed, the server will look for and process (only in the case of 6.1 the following mentioned file is checked. If it is 6.2 they are not checked): Directives
The configuration directives are grouped into three basic sections: Section 1: Global Environment The directives in this section affect the overall operation of Apache, such as the number of concurrent requests it can handle or where it can find its configuration files. ServerType: ServerType is either inetd, or standalone. Inetd mode is only supported on Unix platforms. ServerRoot: The top of the directory tree under which the server's configuration, error, and log files are kept.
NOTE: If you intend to place this on an NFS (or otherwise network) mounted filesystem then please read the LockFile documentation (available at http://www.Apache.org/docs/mod/core.htmllockfile); You will save yourself a lot of trouble. Do not add a slash at the end of the directory path.
LockFile: The LockFile directive sets the path to the lockfile used when Apache is compiled with either
This directive should normally be left at its default value. The main reason for changing it is if the logs directory is NFS mounted, since the lockfile must be stored on a local disk. The PID of the main server process is automatically appended to the filename.
PidFile: The file in which the server should record its process identification number when it starts.
ScoreBoardFile: File used to store internal server process information. Not all architectures require this. But if yours does (you'll know because this file will be created when you run Apache) then you must ensure that no two invocations of Apache share the same scoreboard file. In the standard configuration, the server will process this file, srm.conf, and access.conf in that order. The latter two files are now distributed empty, as it is recommended that all directives be kept in a single file for simplicity. The commented-out values below are the built-in defaults. You can have the server ignore these files altogether by using "/dev/null" (for Unix) or "nul" (for Win32) for the arguments to the directives.
ResourceConfig conf/srm.conf
Timeout: The number of seconds before receives and sends time out.
KeepAlive: Whether or not to allow persistent connections (more than one request per connection). Set to "Off" to deactivate. But we keep it :
MaxKeepAliveRequests: The maximum number of requests to be allowed during a persistent connection. Set to 0 to allow an unlimited amount. We recommend you leave this number high, for maximum performance.
KeepAliveTimeout: Number of seconds to wait for the next request from the same client on the same connection. Server-pool size regulation: Rather than making you guess how many server processes you need, Apache dynamically adapts to the load it sees --- that is, it tries to maintain enough server processes to handle the current load, plus a few spare servers to handle transient load spikes (e.g, multiple simultaneous requests from a single Netscape browser).
It does this by periodically checking how many servers are waiting for a request. If there are fewer than MinSpareServers, it creates a new spare. If there are more than MaxSpareServers, some of the spares die off. The default values are probably OK for most sites.
Number of servers to start initially should be a reasonable ballpark figure.
Limit on total number of servers running: Limit on the number of clients who can simultaneously connect. If this limit is ever reached, clients will be `locked out', so it should not be set too low. It is intended, mainly, as a brake to keep a runaway server from taking the system with it as it spirals down. MaxRequestsPerChild: The number of requests each child process is allowed to process before the child dies. The child will exit so as to avoid problems after prolonged use when Apache (and maybe the libraries it uses) leak memory or other resources. On most systems, this isn't really needed, but a few (such as Solaris) do have notable leaks in the libraries. For these platforms, set to something like 10000 or so; a setting of 0 means unlimited.
NOTE: This value does not include keepalive requests after the initial request per connection. For example, if a child process handles an initial request and 10 subsequent "keptalive" requests, it would only count as 1 request towards this limit.
Listen: Allows you to bind Apache to specific IP addresses and/or ports, in addition to the default. See also the directive.
BindAddress: You can support virtual hosts with this option. This directive is used to tell the server which IP address to listen to. It can either contain "*", an IP address, or a fully qualified Internet domain name. Well that's all for now. In the second part we shall look into Dynamic Shared Object (DSO) Support and also 'Main' server configuration.
Other articles by Vans Information
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