Hypertext transfer protocol ( HTTP ) Apache Server

Apache is the most popular, secure, robust, reliable and powerful web server. Apache is used by more websites than all other web servers combined. RHEL6 includes Apache version 2.2

RHCE6 Exam objectives covered in this article

• HTTP/HTTPS
• Configure a virtual host.
• Configure private directories.
• Deploy a basic CGI application.
• Configure group-managed content.

Installation of Apache  Two packages are required for Apache server

• httpd
• mod_ssl
• elinks

httpd package install Apache web server.
mod_ssl is the additional package which required to create secure websites
elinks is the additional package for text based web browser.

If you have yum repository configured use following command to install Apache web server with additional package

# yum install –y httpd mod_ssl

# yum install elinks

Or you can do it in more simpler way by using groupinsatall. With following command you can install mandatory and all default packages.

# yum groupinstall "Web Server"

If yum repository is not configured use rpm command to install necessary RPM. Mount installation disk of RHEL6 in media folder and move in Packages folder.


Run following command to install httpd

#rpm -ivh httpd* --nodeps --force

Run following command to install mod_ssl

#rpm -ivh mod_ssl* --nodeps --force

Run following command to install elinks

#rpm -ivh elinks* --nodeps --force

Verify that the packages were installed correctly


Run following command to start service when the system boots


Start httpd service


httpd service requires at least one active network connection, if it does not detect any active connection it will throw following message

Starting httpd: httpd: apr_sockaddr_info_get() failed for Server

httpd service try to resolve system IP with domain name. It will throw following error, If it fails to resolve.

httpd: Could not reliably determine the server's fully qualified domain name, using 127.0.0.1 for ServerName

In real world DNS Server are used to bind IP address with domain name. In LAB environment where we have limited systems , we can also use hosts file for this purpose.
Open /etc/sysconfig/network


Change hostname to Server.example.com and save the file


Reboot the system


Verify that hostname is changed


Before we update hosts file on server also verify the hostname and ip address of linuxclient


Now on server open /etc/hosts file


Add entry for server and linuxclient system and save the file


Verify the network card status


Now restart the httpd service


Default versions of httpd create a generic web server service which is sufficient for most basic operations. Once httpd service is running start web browser and enter a URL http://localhost


Same testing can be done form text based web browser ,If GUI is unavailable.

# elinks 127.0.0.1

We got Apache test page which confirm successful Apache configuration.

Exit from the ELinks browser. Press Q, and when the Exit ELinks text menu appears, press Y to exit Elinks.

We have successfully installed Apache Web Server. So far its a generic web server service, to make it a regular and a secure web server, we need to configure it.

IPTABLES Firewall rules for web Server

Default installation of Apache web server use port 80 for HTTP traffic and 443 for HTTPS traffic.

You can create custom iptables rule to limit access to one or more networks or systems. For example following rules allows access to every computers on 192.168.1.0 network except one with IP address 192.168.1.25 over port 80.

-A INPUT -m state --state NEW -m tcp -p tcp -s 192.168.1.25 --dport 80 -j REJECT 

-A INPUT -m state --state NEW -m tcp -p tcp -s 192.168.1.0/24 --dport 80 -j ACCEPT

We have a well written article for IPTABLES firewall, use that to create custom firewall rules for web server. For this article create rules to allow all traffic on port 80 and 443.

#iptables -A INPUT -m state --state NEW -m tcp -p tcp --dport 80 -j ACCEPT 

#iptables -A INPUT -m state --state NEW -m tcp -p tcp --dport 443 -j ACCEPT

Save the firewall rules you have just created and restart the iptables service

# service iptables save 

# service iptables restart

Until you change the value of DocumentRoot directive in httpd.conf file , Apache looks for web pages in default location /var/www/html directory.

To get your web server up and running, all you need to do is to transfer the web pages or websites in /var/www/html directory.

We will make two websites for testing. RHCE exam does not test your ability to make websites. Its only test your ability to configure and run web server. You can use most simple html web page for testing.

Make two directories mysite1 and mysite2 in /var/www/html folder


Make a sample html page in both directories

Our sample websites are ready for use.

 

Configure SELinux for web server

Use following command to check all associated SELinux Booleans with httpd


Most of these options are self explained and relate to interactions with other services. for example httpd_enable_ftp_server allow Apache to act as an FTP server, which is out of scope for this article.


Default enabled SELinux options

Booleans	Descriptions
httpd_builtin_scripting	Used to provide permission for php content
httpd_dbus_avahi	Supports access from HTTP services
httpd_enable_cgi	Allows HTTP services to execute GCI scripts
httpd_tty_comm	Enables communication with controlling terminals
httpd_unified	Supports read/write/execute access by httpd_t files

httpd_enable_homedirs supports access to files from user home directories, default value is off. 

We will enable it later in this article. Default enabled options are sufficient to provide basic web services , you do not need to make any changes. But you need to configure SELinux contexts, user context is system_u and the type is http_sys_content_t.
Check the current context of the files

#ls -Z /var/www 

#ls -Z /var/www/html

We need to set context of any newly created file or directory for the web server user to be able to access it.

Use the chcon command to change the context

#chcon -R -u system_u /var/www/html 

#chcon -R -t httpd_sys_content_t /var/www/html/

Verify that all the context fields have been changed correctly

#ls -Z /var/www/html

Test these websites form linuxclient system [make sure client system have elinks rpm installed]

elinks 192.168.1.1/mystie1/index.htm

Verify the site


Close elinks


On window client open browser and type 192.168.1.1/mysite2/index.htm


We have set up Apache web server with default configuration.
Back up the default httpd.conf file on a safe location.


Open the /etc/httpd/conf/httpd.conf


This is the main configuration file for httpd web service and completely usable right out of the box for generic web service.

This file is grouped in three sections and each section is well commented

• Global environment directives that control the whole operation of Apache server process.
• Directives that define the parameters of the main or default server, which responds to requests that are not handled by a virtual host. These directives also provide default values for the settings of all virtual hosts.
• Settings for virtual hosts, which allow Web requests to be sent to different IP addresses or hostnames and have them handled by the same Apache server process.

To make navigation easier, turn on line number ESC Key + : +set nu + Enter Key

Host-Based Security

If server have multiple IP address, you can limit the IP address and port on which the server can listen for incoming connection. By default server listen on port 80, but can be update as well.


For example to limit server only to listen on IP address 192.168.1.1 with port 80 Set Listen Directive

Listen 192.168.1.1:80

Now Server will listen only on the 192.168.1.1 IP address on port 80 for incoming requests.

Apache also let you configure the hosts which should be allow to access to web server. 

<Directory> section allow you to specify the hosts base security.

Value	Example	Descriptions
Allow from all		Default value, allow access from all hosts
Allow from [IP Address]	Allow from 192.168.1.10	To allow only a specific IP or host
Allow from [Host name]	Allow from linuxclient	To allow only specific host
Allow from [Network]	Allow from .example.com	To allow only example.com network
Allow from [Network]	192.168.1.0/24 192.168.1.0/255.255.255.0	To allow only from 192.168.1.0 network
Deny from all		Deny access from all hosts
Deny from [IP Address]	Deny from 192.168.1.10	To Deny only a specific IP or host
Deny from [Host name]	Deny from linuxclient	To deny only specific host
Deny from [Network]	Deny from .example.com	To deny only example.com network
Deny from [Network]	192.168.1.0/24 192.168.1.0/255.255.255.0	To deny only from 192.168.1.0 network

For exam remember

• If DNS service is unreliable use IP address.
• When specify domain name to allow or deny from, make sure you include the leading dot[.]
• When specify a subnet, there is no ending dot[.] at last octet.
• Order play the most important role, when set allow or deny access.
• If you set Order allow, deny Only those host names or IP addresses associated with allow directive are allowed access. All remaining hosts or IP address would be denied.
• If you set Order deny, allow Only those host names or IP addresses associated with deny directive are denied access. All remaining hosts or IP address would be allowed.

Default value is Allow from all

In our LAB setup we have two clients linuxclient [192.168.1.10], and windowclient [192.168.1.20]. Lets allow access only to linuxclient system.


Save the file and restart the httpd service


Try to access same websites again from both client systems. This time linuxclient system would be able to access web server as usual, but on windowsystem you will be denied

 

User-Based Security

User based authentication provides a way to allow only certain users or group to access web server.

In exam you can use following options to configure user based authentication.

Options	Descriptions
AuthType	Defines the authentication method
AuthName	Comment for the users
AuthUserFile	File used to define username and password
AuthGroupFile	File used to define groups
Require	Specifies the users or groups that can log in

Open httpd.conf file again



In last practice we have restricted all hosts except one


Before we do this exercise lets allow all hosts to access the web server.


In < directory > section add following and save the file

AuthType Basic
AuthName “Password Restricted Area”
AuthUserFile /etc/httpd/userauthfile
Require user rhceuser01

Use htpasswd command to create a userauthfile, that will be holds user accounts.

# htpasswd -cm /etc/httpd/userauthfile rhceuser01

-c Create new file and populates it with first user and password.
-m Passwords will be encrypted in MD5 before saving

Do not use -c options for creating subsequent users, otherwise it will completely override the file. Use -c option only first time for first user, from second users do not use -c option.

Restart the web server


Try again to access same sites from client, this time it will ask for user name and password


If you cancel or use wrong user name and password, access would be denied


Use correct user name and password


Upon successful authentication access would be granted

Secure web server with .htaccess file

In previous exercise we have secured entire sites. However in real life you want to allow certain parts of site publicly accessible, while other by only authenticated users. For this we will use .htaccess file.

Open /etc/httpd/conf/httpd.conf file again


Change AllowOverride directive value to authconfig


In previous example we did user base authentication

Remove that and save the file


Make a directory and file under mysite1

mkdir /var/www/html/mysite1/salary

Suppose that salary folder contains the salary sheet of employees and we want to allow only hr group to access it.

Create a .htaccess file in the salary folder
#vi /var/www/html/mysite1/salary/.htaccess


Add followings and save the file

AuthType Basic
AuthName “Password Restricted Area”
AuthGroupFile /etc/httpd/rhcegroupfile
Require group hr

Now only users from hr group, defined in /etc/httpd/rhcegroupfile can assess this.

Create few more accounts


Create rhcegroupfile, this file will hold entry for groups


Add user accounts in hr group and save file


Update the SELinux context of .htaccess file


Restart the web server


Try again to access site for client, access to other parts of site are allowed except salary


To access salary folder you need to provide user name and password


Upon successful authentication access would be granted

Configure public_html folder in user home directory

httpd.conf file includes a commented directive UserDir public_html just under the default UserDir disable , when it's enabled, it allows users to browse and access the public_html directory within their home folder.

Open /etc/httpd/conf/httpd.conf file


Comment the default directive


Uncomment the UserDir public_html directive and save the file


Now anyone will have access to web pages that a user puts in his ~/public_html directory. This option can be useful if you want each user to share files over the Web. For this option you need to make users home directory executable for world. You also need to make public_html readable and executable. By default this option is disable because this requires a bit of security compromise. So unless you need to be able to share content out of a users home directory, do not enable this option. If you have to enable it in real world, take all caution in setting up this option.

Create a new normal user



Make public_html folder under his home folder and create a test file in public_html folder



Change file permission



Enable SELinux Boolean associated with home directory


Restart the web server


Access it from client system by typing 192.168.1.1/~rh_user1/index.htm

How to create virtual hosts

Virtual host feature of Apache allows you to define multiple web sites on single IP address. For Virtual hosts configuration following options are required

NameVirtualHost	Hostname or IP address of the virtual host
ServerAdmin	Email address of the webmaster
DocumentRoot	Location of the directory, which holds virtual host files
ServerName	URL of the virtual host
ErrorLog	Location for the error log
CustomLog	Location for a custom log

Suppose that we want to host a new website example.com in virtual host.

Make new directory which will hold our new site


Make a sample file in new site


Update SELinux context


Open main configuration file again


By default NameVirtualHost directive is disabled


Enable it


At the end of file in virtual host section add following lines and save the file

<VirtualHost *:80>
ServerAdmin webmaster@example.com
DocumentRoot /webdata/example.com
ServerName example.com
ErrorLog logs/example.com-error_log
CustomLog logs/example.com-access_log common
</VirtualHost>

If you have DNS server configured update the zone files, otherwise update the hosts files . 
On server open the /etc/hosts file


Add entry for new virtual host site and save the file


Restart the httpd service


On linuxclient system you also need to update the hosts file before testing. Open hosts file



Add entry for new virtual host site and save the file


Now use elinks command to browse new site


Test page confirms that we have successfully configured virtual host.

How to deploy a basic CGI application

In this section we will deploy a basic CGI application. RHCE exam objective "Deploy a basic CGI application", does not test your programming skills, so you need not to worry about programming language. You only need to know the method.

Create a directory to hold your web application:

# mkdir /var/www/webapp

Make a new sample perl file


Add following in file and save the file. [This will make a sample perl script to print hello, world. Based on Apache manual]

#!/usr/bin/perl
print "Content-type: text/html\n\n";
print "Hello, World!";

Update file permission and SELinux context


Open configuration file
 

At end of file add following and save the file

ScriptAlias /webapp "/var/www/webapp"
<Directory "/var/www/webapp/">
Options ExecCGI FollowSymLinks
Order allow,deny
Allow from all
</Directory>

Restart the web server


On client now you can access this CGI application.

 

Configure secure virtual host

In this last section of tutorial we will configure a secure virtual host with self signed certificate. Make a directory to host our secure site


Make a sample index.htm file in it


Change file permission and Update SELinux context


Open main configuration file /etc/httpd/conf.d/ssl.conf


Make sure Listen Directive remain on


Add new Directive NameVirtualHost *:443 just above the <VirtualHost _default_:443> and replace _default_ with * in <VirtualHost _default_:443> tag.Uncomment the DocumentRoot and ServerName directives.

 Change the value of directives and save the file

Move in certificate holder directory /etc/pki/tls/certs and use genkey command to generate new certificate and private key for secure site


Select Next and press enter on Keypair generation window


During the exam always choose minimum available key size. Even smaller key size can take up to several minutes and in exam every minute is precious. Select 512 and move to Next tab and press enter


Wait while key generates


Select No and press enter on Generate CSR window


Keep default details and select Next and press Enter


We have sucessfully created the certificate ,now we to update the hosts file on server



Restart the httpd service


On client updated the hosts file



To test secure site open the web browser and type https://host1.example.com/index.htm in URL


You will see Untrusted connection screen Unless you purchase an actual certificate from a certificate authority (CA) such as VeriSign and Thawte. For RHCE exam we do not need third party certificate, as we have self signed certificate. Click on I Understand the Risks and Click on Add Exception



Click on confirm security exception


Test page confirms that we have successfully configured the secure virtual host

To test secure sites form elinks test based browser we need to comment two standard directives


open /etc/elinks.conf file


You need to comment these directives


Comment them and save the file



Now you can access secure sites form elinks as well


Test page confirms our secure web hosting


When you restarts the httpd service, restart process actually stop the service from running before starting it again. This process hardly take few seconds that is ok for exam purpose but in real life where thousands of people are hitting your site, you can't afford any outage even its in seconds. In that situation you can use reload option which allows the main configuration to reread without the actually bringing service down.

#service httpd reload

One more important option which should know for real world is graceful

#service httpd graceful

This option reread the new configuration file without disconnecting any currently connected users. Only drawback of this option is that the currently active connections use the old configuration file until they terminate their connection and reconnect.
One more cool options is configtest, when used , service parses the main config file for any errors and reports back if something is found. It's your helping hand during the exam to detect any syntax errors in configuration file.

# service httpd configtest 

Syntax OK 

If this command detect any syntax related error it return with that, otherwise it return with Syntax ok.

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