Below is a simple Markdown tutorial for configuring Apache to run two PHP versions (PHP 7.4 and PHP 8.0) concurrently using PHP-FPM. This assumes you're using a Linux system with Apache.

Running Multiple PHP Versions with Apache and PHP-FPM

before starting, check if we already has two php version

sudo update-alternatives --display php

Prerequisites

• Linux server (Ubuntu used in this example)
• Apache web server
• PHP 7.4 and PHP 8.0 installed

Install Apache

sudo apt-get update
sudo apt-get install apache2

Add Ondrej Repository (if needed)

sudo add-apt-repository ppa:ondrej/php
sudo apt update

if got add-apt-repository: command not found
install software properties common first

sudo apt-get update
sudo apt-get install software-properties-common

Install PHP Versions

sudo apt-get install php7.4 php7.4-fpm php7.4-mysql php7.4-pdo php7.4-gd php7.4-curl php7.4-json php7.4-xml php7.4-mbstring php7.4-zip php7.4-opcache php7.4-intl php7.4-imagick php7.4-soap
sudo apt-get install php8.0 php8.0-fpm php8.0-cli php8.0-mysql php8.0-xml php8.0-mbstring php8.0-bcmath php8.0-curl php8.0-tokenizer php8.0-intl php8.0-readline php8.0-ctype php8.0-gd

sudo apt-get install php8.1 php8.1-fpm php8.1-cli php8.1-mysql php8.1-xml php8.1-mbstring php8.1-bcmath php8.1-curl php8.1-tokenizer php8.1-intl php8.1-readline php8.1-ctype php8.1-gd

Enable Apache Modules

sudo a2enmod proxy_fcgi actions
sudo systemctl restart apache2

Configure PHP-FPM Sockets

Check the PHP-FPM configuration files for the listening sockets:

grep -R "^listen" /etc/php/7.4/fpm/pool.d/
grep -R "^listen" /etc/php/8.0/fpm/pool.d/

Configure Apache Virtual Hosts

Create Virtual Host configuration files for each PHP version:

/etc/apache2/sites-available/php74.example.com.conf

<VirtualHost *:80>
    ServerName php74.example.com
    DocumentRoot /var/www/php74.example.com

    <FilesMatch \.php$>
        SetHandler "proxy:unix:/var/run/php/php7.4-fpm.sock|fcgi://localhost/"
    </FilesMatch>

    <Directory /var/www/php74.example.com>
        Options Indexes FollowSymLinks
        AllowOverride All
        Require all granted
    </Directory>
</VirtualHost>

/etc/apache2/sites-available/php80.example.com.conf

<VirtualHost *:80>
    ServerName php80.example.com
    DocumentRoot /var/www/php80.example.com

    <FilesMatch \.php$>
        SetHandler "proxy:unix:/var/run/php/php8.0-fpm.sock|fcgi://localhost/"
    </FilesMatch>

    <Directory /var/www/php80.example.com>
        Options Indexes FollowSymLinks
        AllowOverride All
        Require all granted
    </Directory>
</VirtualHost>

Enable Virtual Hosts

sudo a2ensite php74.example.com
sudo a2ensite php80.example.com
sudo systemctl restart apache2

Create Document Roots

sudo mkdir /var/www/php74.example.com
sudo mkdir /var/www/php80.example.com

Test Configuration

Create index.php files in the document roots:

<?php phpinfo(); ?>

Visit http://php74.example.com and http://php80.example.com in your browser to verify the PHP versions.

install common php7.4 extension if you got extension error

sudo apt-get install php7.4-mysql php7.4-pdo php7.4-gd php7.4-curl php7.4-json php7.4-xml php7.4-mbstring php7.4-zip php7.4-opcache php7.4-intl php7.4-imagick php7.4-soap

Run manual change CLI version

https://gridpane.com/kb/setting-the-cli-php-version/

Checking Your CLI PHP Version
To check your CLI PHP version, you can run the following command:

sudo update-alternatives --display php

This will output the following, only with the correct PHP version should your setting be different:

root@servername:~# sudo update-alternatives --display php
php - manual mode
link best version is /usr/bin/php8.1
link currently points to /usr/bin/php7.4
link php is /usr/bin/php
slave php.1.gz is /usr/share/man/man1/php.1.gz
/usr/bin/php7.3 - priority 73
slave php.1.gz: /usr/share/man/man1/php7.3.1.gz
/usr/bin/php7.4 - priority 74
slave php.1.gz: /usr/share/man/man1/php7.4.1.gz
/usr/bin/php8.0 - priority 80
slave php.1.gz: /usr/share/man/man1/php8.0.1.gz
/usr/bin/php8.1 - priority 81
slave php.1.gz: /usr/share/man/man1/php8.1.1.gz
root@servername:~#

Changing Your CLI PHP Version on Nginx or OpenLiteSpeed

NGINX AND OPENLITESPEED UPDATE
As of November 8th 2022, setting the PHP CLI version on both Nginx and OpenLiteSpeed has been brought to parity so that the same commands work on both server stacks.

STEP 1. SET YOUR PREFERRED CLI PHP VERSION
Run the following command to change the PHP CLI version:

sudo update-alternatives --set php /usr/bin/phpX.X

X.X = the version number, for example: 7.4, 8.0, 8.1.

For example:

sudo update-alternatives --set php /usr/bin/php7.4

STEP 2. MAKE THE CHANGE PERSIST
Our systems check for a token file for the CLI PHP version. If it’s not present, your changes will be reverted. Create the token file with:

/root/preferred_php_cli.version

Add the PHP version – number only. For example:

7.4

Now save the file with CTRL+O followed by Enter. Exit nano with CTRL+X.

Interchange php version on Apache

To ensure that Apache is using PHP 8.0 instead of PHP 7.4, you need to disable the PHP 7.4 module and enable the PHP 8.0 module for Apache. Here are the steps:

1. ensure apache extension for both php is isntalled

   sudo apt-get install libapache2-mod-php7.4
   sudo apt-get install libapache2-mod-php8.0

2. Disable the PHP 7.4 module:

sudo a2dismod php7.4

2. Enable the PHP 8.0 module:

sudo a2enmod php8.0

3. Restart Apache to apply the changes:

sudo systemctl restart apache2

4. Verify the PHP version used by Apache by creating a phpinfo.php file in your web root directory:

echo "<?php phpinfo(); ?>" | sudo tee /var/www/html/phpinfo.php

Then, navigate to http://your-server-ip/phpinfo.php in your web browser. It should display information about PHP 8.0.

If you still see PHP 7.4, double-check that the PHP 8.0 packages and the Apache module for PHP 8.0 are installed correctly.

conclusion

Please adjust paths, domain names, and configurations based on your specific setup.

defautl php running is the first installed php so consider which version you use when chosing which one to install first