Web Server (Apache httpd )

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Apache Web Server• A PAtCHy server: developed by the Apache group• History-http://httpd.apache.org/ABOUT_APACHE.html• First official public release (0.6.2) in April 1995• Add adaptive pre-fork child processes (very

important!).• Port to multiple platforms. Add documentation.• Apache 1.0 was released on 12/1/95.

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Compiling httpd-2.2.0• Download httpd-2.2.0.tar.bz2 from http://www.apache.org/dist or closer

mirror sites• $tar xjf httpd-2.2.0.tar.bz2• $ ./configure --prefix=PREFIX• $ make• $ make install• $ PREFIX/bin/apachectl start

• Here PREFIX is the prefix of the directory containing the distribution, typically it is /usr/local/apache.Since as a normal user, we donot have permission to install there, I specify PREFIX as /users/server/students/cs526/public_html/apache2.2m/httpd-2.2.0

• For configuring the apache with specific features, we can specify the corresponding features as option to the configure command. You can find the list of features by “./configure –help”

• Here is the command we used to compile the htttpd with proxy and cache modules we need.

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Apache Exercises • Each site.<exercise> directory contains

– conf: configuration files, httpd.conf, mime.types– htdocs: contains web pages– logs: access_log, error_log, httpd.pid– cmd: alias of “<path>httpd -d

serverrootDirectory -X”Here <path> specify the directory contains the httpd program-d specifies the server root directory, -X single process execution

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Httpd Configuration File• Apache uses a set of directives to tell httpd

how the web site should be configured. http://www.apache.org/docs/mod/directives.html

Each Apache configuration directive is described using a common format that looks like this:

Syntax: directive-name some args Default: directive-name default-value Context: context-list Override: override Status: status Module: module-name

Compatibility: compatibility notes

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Block Directives• Directives that limit the application of other

directives.• Specify by a group like a tag section in html.• <VirtualHost host[:port]>

...</VirtualHost>

• <VirtualHost…><Directory dir>, <Files file>, <Location URL> in ascending order of authority. <Location> can overwrite others.

• dir, file, URL can specify using wildcards and full regular expressions preceded by “~”

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List of Directives • User, Group: specify user and group that httpd runs on.• ServerName: hostname of server• ResourceConfig, AccessConfig: for reading additional

related directives. Can be disabled by /dev/null as value• Listen: specify the port httpd run on (Port directive is

deprecated)• ServerAdmin:email addr. for browser to do automatic

replies.• DocumentRoot:• TransferLog, ErrorLog, PidFile: where access,error logs,

httpd.pid should be located.

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Performance Related Directives• KeepAlive [on|off](on): keep connection alive for n requests

before terminate provided they come in before timeout. n is defined in MaxKeepAliveRequests <n>(100) directive

• KeepAliveTimeout <n>(15): wait for the next request for n seconds before terminate the connections.

• Timeout <n>(300): max. time in sec for a block data.• HostNameLookups [on|off|double](off): do reverse DNS lookup

for logging the domain name of the request.• MaxClients <n>(256): the limit of # of simultaneous requests

(hence the # of child processes).• MaxRequestsPerChild <n>(0): Spare(child) server dies after <n>

requests, avoid mem leak. 0 mean infinite requests.

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Web Hosting• There are a few way we can host a web site:

– Named-based Virtual Hosting – IP-based Virtual Hosting– Virtual Machine Virtual Hosting

• Name-based Virtual Hosting– A set of hostnames shared the same IP address (similar to alias)– utilize the HOST: meta header in http request (browser fill in the hostname) to

distinguish different web site.– Each hostname will have its own site configuration, document root.– Require either the set of hostnames are registered DNS names or the client

machines need to configure their ip addresses mapping in hostfiles such as /etc/hosts (Unix) or C:\WINDOWS\system32\drivers\etc\hosts (Windows)

• IP-based virtual Hosting:– Require a unique IP address for each virtual hosting site– Use IP alieas to configure the same Network Interface Card (NIC) to listen to

different IP address, e.g., ifconfig eth0:1 128.198.160.33– Some Unix system sets limit on how many IP aliases can be supported.

• Use <VirtualHost hostname[:port]> block directives• Specify ServerAdmin, DocumentRoot, ServerName, ErrorLog, TransferLog

for individual VH

Virtual Hosts• The apache server can handle multiple “web sites” at a time

– a web service provider company may have multiple different sites to offer (see figure 6-2)

– a single company may wish to partition their web site into multiple domains (e.g., sales, accounting, management, research, etc) (see figure 6-1)

– a single organization may wish to give each user their own web site

• In any of these cases, the idea is to have the web server create several virtual hosts – although in the last case, we just divide the file space up

• We use the <VirtualHost> container for this, which allows each “host” to have their own server-specific configuration– we can divide our hosts up based on IP addresses or IP aliases– the container looks like this: <VirtualHost ipaddress>

ServerName ipalias DocumentRoot path</VirtualHost> 10

IP-Based• Assume that we want each of our servers to have a

unique IP address– in fact, we will have to set up the DNS entries so that all

of the different IP addresses resolve to the same IP address, that of our web server

• see figure 6-3• Now we place in our httpd.conf file <VirtualHost>

containers for each server– one container per server– this allows us to add more servers over time (or remove

servers) just by modifying the httpd.conf file• each virtual host will apply the overall server configuration but

you can also specify server-specific directives for each virtual host as is needed

• many of the directives we saw from chapter 5 that dealt with 1 server can be applied to any, each or some combination of servers

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More• Each <VirtualHost> container will have its own unique IP address

• To the right, you see three different servers

• Notice how each server maps to a different location under DocumentRoot

• We might create symbolic links so that each company can edit their own directory from a location that they are more familiar with

• We can also set up our various servers to respond to different ports of the same IP address (see the right below)

<VirtualHost 172.19.31.1> ServerName www.company1.com DocumentRoot /home/company1</VirtualHost><VirtualHost 172.19.31.2> ServerName www.company2.com DocumentRoot /home/company2</VirtualHost><VirtualHost 172.19.31.3> ServerName www.company3.com DocumentRoot /home/company3</VirtualHost>

<VirtualHost 172.19.31.1:80> ServerName www.company1.com DocumentRoot /home/company1</VirtualHost><VirtualHost 172.19.31.1:8080> ServerName www.company2.com DocumentRoot /home/company2</VirtualHost> 12

Name-Based• If we want all of our servers

to share the same IP address, there is only one major difference required to the apache server– we must add the directive

NameVirtualHost ipaddress to our httpd.conf file where ipaddress is the shared IP address of all servers

• this same address will be placed in each server’s <VirtualHost> container

• We will also have to ensure that all DNS servers resolve any of the servers’ aliases to this same address

NameVirtualHost 172.19.31.1

<VirtualHost 172.19.31.1> ServerName www.company1.com DocumentRoot /home/company1</VirtualHost><VirtualHost 172.19.31.1> ServerName www.company2.com DocumentRoot /company2</VirtualHost><VirtualHost 172.19.31.1> ServerName www.company3.com DocumentRoot /home/company3</VirtualHost>

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More• We can use the name-based approach to allow multiple alias names to map to the same server by supplying numerous ServerAlias directives within a VirtualHost container– for instance, imagine that

www.company1.com wishes to also be recognized by company1.com, www.company1.org, www.company1.net and sales.company1.com

• We can also permit the * or ? wildcard to save on the number of entries we might want to put into our container– however, this can easily result in

problems with respect to have misspelled server names map to the wrong thing

<VirtualHost 172.19.31.1> ServerName www.company1.com ServerAlias company1.com ServerAlias www.company1.org ServerAlias www.company1.net ServerAlias sales.company1.com DocumentRoot /home/company1</VirtualHost>

Or<VirtualHost 172.19.31.1> ServerName www.company1.com ServerAlias company1.com ServerAlias *.company1.com ServerAlias www.company1.* DocumentRoot /home/company1</VirtualHost>

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Some Additional Comments• If we just add the previous entries into our httpd.conf file,

it does us no good unless we also ensure that DNS entries have the same mappings– for instance, if you are at site X and issue an http request for

www.company1.org, if the DNS for site X does not map www.company1.org to 172.19.31.1, then the http request never makes it to our server for processing!

– so we have to make sure that the DNS tables across the Internet reflect the proper mappings

• we have already set up a BIND server, so we will explore this in the next labs

• You can use both IP-based and Name-based virtual hosts if desired by having some VirtualHosts share the same IP address and others have different addresses– this will require that you use NameVirtualHost for any shared

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Continued• If you are using name-based virtual hosts, then any

http request that reaches your server will already have had the IP address resolved– because of this, we do not have to put IP addresses in our

VirtualHost containers, but can replace them with * • the * will match any IP address• only do this with the name-based approach, if you use the IP-

based approach, then each virtual host maps to a unique address

• If your computer has multiple IP addresses (e.g., an internal address and an external address)– you can place all IP addresses in the VirtualHost

container (and the NameVirtualHost directive)• NameVirtualHost 172.19.31.12• NameVirtualHost 10.11.31.12• <VirtualHost 172.19.31.12 10.11.31.12> … </VirtualHost> 16

Include Files• Recall that not all directives need to be placed in

the httpd.conf file– in fact, for virtual hosts, you would not want this

because each server’s web administrator(s) will need to edit the configuration file for that server

• if all directives were shared in one file, then you would have to give many different people access to that one file

– therefore, we allow the administrators to place these server-wide directives in a different file, which is then included with the httpd.conf directives via include directives

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Overriding httpd.conf Directives• Recall that the outermost context is the server’s settings

– we do not want our individual administrators to have access to httpd.conf but we want to allow them to have their own specific directives in their include files

– so, in our httpd.conf file, we need to add the AllowOverride directive to any DocumentRoot directory

• for instance, in the <VirtualHost> container for company1, you will add <Directory /home/company1> and place the AllowOverride All directive in that container

– the question is, do we want to use “All” in our AllowOverride or be more specific?

• AllowOverride can have None, All, or any subset of this list:

– AuthConfig, FileInfo, Indexes, Limit, Options

• see the example to the right

<Virtualhost 172.19.31.1> ServerName www.company1.com DocumentRoot /home/company1 <Directory /home/company1> AllowOverride Indexes Options </Directory></VirtualHost> 18

ExampleNameVirtualHost 172.19.31.12<Directory /var/www/hosts>

Order allow,deny Deny from all</Directory><VirtualHost 172.19.31.12>

ServerName www.company1.comDocumentRoot /var/www/hosts/company1<Directory /var/www/hosts/company1>

AllowOverride allAllow from all

</Directory></VirtualHost><VirtualHost 172.19.31.12>

ServerName www.company2.comDocumentRoot /var/www/hosts/company2<Directory /var/www/hosts/company2>

AllowOverride allAllow from all

</Directory></VirtualHost>

Establish protection fordirectories above anyvirtual host’s directory

Override any directives andprotection from the previousdirectory

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Web Site Structure

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Virtual Host Performance and Status• The only real drawback to using virtual hosts is that

the more hosts you have, the worse the server’s performance will be– running 10 servers instead of 1 will probably result in 10

times the number of requests to service and thus the server will be 10 times more busy

– running 10 servers instead of 1 will probably require 10 times the amount of disk usage

• an ISP that wishes to provide web server services will have to take this into account when purchasing server hardware

• To determine the status of the various servers, use httpd –S which will list – IP address and port (if different from the default server)– name of the server– location of DocumentRoot for the given server

• we will examine status information in more detail in chapter 721

Remember

• Basic Configurations• Virtual Hosting & its Types

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