Two Copies of Apache (Apache: The Definitive Guide)

3.9. 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 for the sake of completeness, here it is. Normally, you would only bother if the different virtual hosts needed 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 try to avoid running more than one copy, as doing so will generally load the machine more.

In our case, we don't have any real need to run two copies; however, we will go this route for the sake of education. 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/site.twocopy/customers/htdocs
BindAddress www.butterthlies.com
TransferLog logs/access_log

In ... /sales the Config file is:

User webuser
Group webgroup
ServerName sales.butterthlies.com
DocumentRoot /usr/www/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 do this.

3.9.1. 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.

3.9.2. 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 really you should 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 the virtual host listens on -- that is done by the <VirtualHost> directive itself.

3.9.3. 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.

3.9.4. ListenBacklog

ListenBacklog number
Default: 511
Server config

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(2).

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 11, "What's Going On?" , the information stored in these logs can be tuned.

3.9.5. ServerType

ServerType [inetd|standalone]
Default: standalone
Server config

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

http stream tcp nowait root /usr/local/bin/httpd httpd -d directory

standalone

Having set up the customers, we can duplicate the block, making some slight changes to suit the salespeople. The two servers have different DocumentRoots, 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 do not 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; 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 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 (on FreeBSD hit ALT-F1), get into ... /customers and type:

% ./go

The first Apache is running. Now get into .../customers and again type:

% ./go

Now, 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 commerce!