Introduction to the Apache Web Server - ApacheCon

Section 3
Starting and Stopping
http://httpd.apache.org/docs/invoking.html
http://httpd.apache.org/docs/stopping.html
In this section we discuss the utilities for starting and stopping Apache, including persuading Apache to
start when your system boots up. Along the way, we’ll talk about the various Apache process architectures,
and how to choose the one that’s right for you.
3.1 Apache process architecture
It is useful to understand the Apache architecture before we go much farther.
While this may seem like a bit of a tangent, this is by far the best place to put this in, and helps understand
some basic things about how Apache uses your system. It also helps understand why you have to start it as
root, but why this is still secure, as well as numerous other things which will be useful in the long run.
This section is also crucial for understanding many future sections, such as performance, the User and Group
directives, and security.
3.1.1 Apache 1.3
With Apache 1.3, Apache runs as multiple processes, each of which is capable of handling incoming HTTP
requests. A single parent process, running as root, manages the pool of available servers, creating new ones
as they are needed, and reaping excess ones when load is reduced.
The size of this pool of servers is controlled by the directivesMinSpareServers and MaxSpareServers, which
specify how many idle processes there should be at any given time. When a new client request comes in, one
of the idle processes is delegated to handle that request. If this causes the number of idle processes to dip
below MinSpareServers, then Apache will create a new child process to add to the pool. Likewise, when
a client disconnects, Apache will, if necessary, kill off child processes to ensure that there are no more than
MaxSpareServers idle processes in the pool.
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