This article introduces you to vhost and server block basics.

Check the web server status

The most common web servers that run on Linux® are Apache®
(httpd or apache2) and NGINX®. Plesk® is a GUI
platform for managing websites. If you have Plesk installed, use
this article as a guide to understand vhosts.

By default, web servers allow HTTP traffic through port 80 and HTTPS
(secure) traffic through port 443.

To find the webserver that runs on ports 80 and 443, enter the following command:

# netstat -plnt | awk '$4 ~ /:(80|443)$/'
tcp6       0      0 :::80                   :::*                    LISTEN      2549/httpd
tcp6       0      0 :::443                  :::*                    LISTEN      2549/httpd

To check the the status of a webserver, run one of the commands shown in the
following table:

In Plesk, to check the status and identify which web server is in use, enter the following command:

# service psa status; netstat -plnt | awk '$4 ~ /:(80|443)$/'

Check the vhosts configuration

A web server (or a pool of web servers) can host several websites by using Virtual Hosts
(vhosts). Vhosts allow several websites to share resources from a physical server.

Vhosts can be IP-based or name-based. IP-based vhosts assign a different IP address to a website,
and name-based vhosts assign multiple hostnames to a single IP address. Vhosts keep track of
websites in a web server, specifying the configuration of each website.

To check the vhosts configuration in Apache, enter one of the following commands:

# httpd -S

or

# apache2ctl -S
*:80                   example.com (/etc/httpd/vhost.d/example.com.conf:1)

To read the contents of a vhost configuration file, enter the following command:

# cat /etc/httpd/vhost.d/example.com.conf 

Entries in the vhosts configuration file include:

• :80 or :443: These entries specify if the website uses HTTP (80) or HTTPS (443).
• DocumentRoot: The directory path of the website files.
• ServerName: The website domain name.
• ServerAlias: Any other website domain name which you want to redirect to the
  ServerName domain. You usually use domains of the type www.domain, but you can
  also use other domains or subdomains.
• ErrorLog: The directory path and name of error logs.
• Port 443: The SSL configuration. Comment this section if the website does not have
  a valid SSL certificate.
• SSL files: The three SSL file paths needed for a secure HTTPS server.

The following example shows a vhosts configuration file:

<VirtualHost *:80>
    DocumentRoot "/var/www/vhosts/example.com/httpdocs"
    ServerName "example.com"
    ServerAlias "www.example.com"
    <Directory /var/www/vhosts/example.com/httpdocs>
        AllowOverride All
        Options +FollowSymlinks
    </Directory>
 
    DirectoryIndex index.html index.php index.htm
 
    # Logging
    CustomLog /var/log/httpd/example.com-access_log combined
    ErrorLog /var/log/httpd/example.com-error_log
</VirtualHost>
 
#<VirtualHost *:443>
#    DocumentRoot "/var/www/vhosts/example.com/httpdocs"
#    ServerName "example.com"
#    ServerAlias "www.example.com"
#    <Directory /var/www/vhosts/example.com/httpdocs>
#        AllowOverride All
#        Options +FollowSymlinks
#    </Directory>
 
#    DirectoryIndex index.html index.php index.htm
 
#    # SSL Configuration
#    SSLEngine On
#    SSLCertificateFile /etc/httpd/conf/ssl.crt/2021-example.com.crt
#    SSLCACertificateFile /etc/httpd/conf/ssl.crt/2021-example.com.ca
#    SSLCertificateKeyFile /etc/httpd/conf/ssl.key/2021-example.com.key
#
#    # Logging
#    CustomLog /var/log/httpd/example.com-ssl_access_log combined
#    ErrorLog /var/log/httpd/example.com-ssl_error_log
#</VirtualHost>

To copy the configuration file of an existing vhost to create a new one,
enter the following command:

# cat /OLD_DOMAIN.conf | sed 's/OLD_DOMAIN/NEW_DOMAIN/ig' >> /NEW_DOMAIN.conf

Edit the new vhost configuration file as required. For example, you might
need to comment the settings that make port 443 active.

To find the location of DocumentRoot in a vhost configuration file,
enter the following command:

# grep Doc /etc/httpd/vhost.d/example.com.conf

DocumentRoot /var/www/vhosts/example.com

Make a new vhost

Use the following instructions to make a new vhost:

1. If possible, copy an existing vhost to keep consistent settings. Use a text
   editor or tool like vim, nano, sed, or awk`.

2. Make a new DocumentRoot directory. The system makes the custom and error logs
   automatically. Run the following command:

   # mkdir -p /docroot
   

3. Check that the web server does not send any errors:

   httpd -t

4. Do a graceful restart on the web server to incorporate the changes with minimal
   disruption to your live environment:

   # service httpd graceful
   

5. Check the web server again:

   httpd -t; service httpd status

Check and troubleshoot changes to the vhost configuration

To check mistakes in Apache, use either one of the following commands:

# httpd -t

or

# apache2ctl -t

AH00558: httpd: Could not reliably determine the server's fully qualified
domain name, using 127.0.0.1. Set the 'ServerName' directive globally to
suppress this message
Syntax OK

To check mistakes in NGINX, use the following command:

# nginx -t

AH00558: httpd: Could not reliably determine the server's fully qualified
domain name, using 127.0.0.1. Set the 'ServerName' directive globally to
suppress this message
Syntax OK

Note: The clause Could not reliably determine is common, and it doesn't
mean an error. You can usually ignore it.

The following example shows a sample error:

# httpd -t
AH00112: Warning: DocumentRoot [/var/www/vhosts/example.com] does not exist
AH00558: httpd: Could not reliably determine the server's fully qualified
domain name, using 127.0.0.1. Set the 'ServerName' directive globally to
suppress this message
Syntax OK

Fix this error by creating a DocumentRoot:

# mkdir -p /var/www/vhosts/example.com

Another example error:

# httpd -t
AH00526: Syntax error on line 5 of /etc/httpd/vhost.d/example.com.conf:
Invalid command 'oops', perhaps misspelled or defined by a module not
included in the server configuration

The word oops is in the vhost file, and Apache does not know how to interpret it.
You can use vim, nano, or another text editor to fix the error.

Restart a web server

The web server acknowledges the changes made to the vhosts configuration after a restart.
The current threads can finish before the restart occurs with the graceful option.

To do a graceful restart on Apache, enter one of the following commands:

# service httpd graceful

or

# service apache2 graceful

The following are best practices to avoid service interruptions after
changing the vhosts configuration:

• Back up the webserver.
• Make the changes.
• Do a graceful restart.
• Ensure that the webserver runs without errors.

It is important to avoid as much downtime as possible in a live environment,
which means that after restarting the web server, you should perform the checks
as quickly as possible. To do this, group all the commands on one line.

To do a graceful restart on Apache and check for errors, enter either one of the following commands:

# service httpd graceful; httpd -t; service httpd status | grep running

or

# service apache2 graceful; apache2ctl -t; service apache2 status | grep running

AH00558: httpd: Could not reliably determine the server's fully qualified domain
name, using 127.0.0.1. Set the 'ServerName' directive globally to suppress this message
Syntax OK
Redirecting to /bin/systemctl status httpd.service
Active: active (running) (Result: exit-code) since Mon 2021-01-18 12:53:06 GMT; 2 months 19 days ago

To restart NGINX and check that it's running, enter the following commands:

# nginx -s reload; nginx -t; service nginx status

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