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4.3. Two Copies of Apache
To illustrate the possibilities, we will run two copies of Apache with different IP addresses on different consoles, as if they were on two completely separate machines. This is not something you want to do often, but on a heavily loaded site it may be useful to run two Apaches optimized in different ways. The different virtual hosts probably need very different configurations, such as different values for ServerType, User, TypesConfig, or ServerRoot (none of these directives can apply to a virtual host, since they are global to all servers, which is why you have to run two copies to get the desired effect). If you are expecting a lot of hits, you should avoid running more than one copy, as doing so will generally load the machine more.
You can find the necessary machinery in ... /site.twocopy. There are two subdirectories: customers and sales.
The Config file in ... /customers contains the following:
User webuser Group webgroup ServerName www.butterthlies.com DocumentRoot /usr/www/APACHE3/APACHE3/site.twocopy/customers/htdocs BindAddress www.butterthlies.com TransferLog logs/access_log
In .../sales the Config file is as follows:
User webuser Group webgroup ServerName sales.butterthlies.com DocumentRoot /usr/www/APACHE3/APACHE3/site.twocopy/sales/htdocs Listen sales-not-vh.butterthlies.com:80 TransferLog logs/access_log
On this occasion, we will exercise the sales-not-vh.butterthlies.com URL. For the first time, we have more than one copy of Apache running, and we have to associate requests on specific URLs with different copies of the server. There are three more directives to for making these associations:
| BindAddress |
BindAddress addr Default addr: any Server config
This directive forces Apache to bind to a particular IP address, rather than listening to all IP addresses on the machine. It has been abolished in Apache v2: use Listen instead.
| Port |
Port port Default port: 80 Server config
When used in the main server configuration (i.e., outside any <VirtualHost> sections) and in the absence of a BindAddress or Listen directive, the Port directive sets the port number on which Apache is to listen. This is for backward compatibility, and you should really use BindAddress or Listen.
When used in a <VirtualHost> section, this specifies the port that should be used when the server generates a URL for itself (see also ServerName and UseCanonicalName). It does not set the port on which the virtual host listens — that is done by the <VirtualHost> directive itself.
| Listen |
Listen hostname:port Server config
Listen tells Apache to pay attention to more than one IP address or port. By default, it responds to requests on all IP addresses, but only to the port specified by the Port directive. It therefore allows you to restrict the set of IP addresses listened to and increase the set of ports.
Listen is the preferred directive; BindAddress is obsolete, since it has to be combined with the Port directive if any port other than 80 is wanted. Also, more than one Listen can be used, but only a single BindAddress.
There are some housekeeping directives to go with these three:
ListenBacklog
ListenBacklog sets the maximum length of the queue of pending connections. Normally, doing so is unnecessary, but it can be useful if the server is under a TCP SYN flood attack, which simulates lots of new connection opens that don't complete. On some systems, this causes a large backlog, which can be alleviated by setting the ListenBacklog parameter. Only the knowledgeable should do this. See the backlog parameter in the manual entry for listen.
Back in the Config file, DocumentRoot (as before) sets the arena for our offerings to the customer. ErrorLog tells Apache where to log its errors, and TransferLog its successes. As we will see in Chapter 10 , the information stored in these logs can be tuned.
ServerType
The ServerType directive allows you to control the way in which Apache handles multiple copies of itself. The arguments are inetd or standalone (the default):
- inetd
- You might not want Apache to spawn a cloud of waiting child processes at all, but rather to start up a new one each time a request comes in and exit once it has been dealt with. This is slower, but it consumes fewer resources when there are no clients to be dealt with. However, this method is deprecated by the Apache Group as being clumsy and inefficient. On some platforms it may not work at all, and the Group has no plans to fix it. The utility inetd is configured in /etc/inetd.conf (see man inetd ). The entry for Apache would look something like this:
http stream tcp nowait root /usr/local/bin/httpd httpd -d directory- standalone
- The default; this allows the swarm of waiting child servers.
Having set up the customers, we can duplicate the block, making some slight changes to suit the salespeople. The two servers have different DocumentRoot s, which is to be expected because that's why we set up two hosts in the first place. They also have different error and transfer logs, but they don't have to. You could have one transfer log and one error log, or you could write all the logging for both sites to a single file.
Type go on the server (this may require root privileges); while on the client, as before, access http://www.butterthlies.com or http://sales.butterthlies.com /.
The files in ... /sales/htdocs are similar to those on ... /customers/htdocs, but altered enough so that we can see the difference when we access the two sites. index.html has been edited so that the first line reads:
<h1>SALESMEN Index to Butterthlies Catalogs</h1>The file catalog_summer.html has been edited so that it reads:
<h1>Welcome to the great rip-off of '97: Butterthlies Inc</h1> <p>All our worthless cards are available in packs of 20 at $1.95 a pack. WHAT A FANTASTIC DISCOUNT! There is an amazing FURTHER 10% discount if you order more than 100. </p> ...and so on, until the joke gets boring. Now we can throw the great machine into operation. From console 1, get into ... /customers and type:
% ./goThe first Apache is running. Now get into .../sales and again type:
% ./goNow, as the client, you log on to http://www.butterthlies.com / and see the customers' site, which shows you the customers' catalogs. Quit, and metamorphose into a voracious salesperson by logging on to http://sales.butterthlies.com /. You are given a nasty insight into the ugly reality beneath the smiling face of e-commerce!
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| 4.2. Virtual Hosts |  | 4.4. Dynamically Configured Virtual Hosting |
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