I am using Nginx as a reverse proxy with Apache. I have a domain, let's say example.com that is pointing at the /var/www/html/example directory.

I want to point a sub-domain phpmyadmin.example.com to a directory /var/www/html/phpmyadmin that is clearly not a sub-directory of the domain's directory.

My complete configuration file /etc/nginx/sites-enabled/example is shown below. I added the parts between ##### BEGIN .. and ###### END .. to my configuration file to try to make this work.

Then I did sudo service nginx restart to restart NGINX successfully but I still cannot access phpmyadmin.example.com.

Here's my configuration:

server {

    root /var/www/html/example;



    # Add index.php to the list if you are using PHP

    index index.php index.html index.htm index.nginx-debian.html;



    server_name example.com;



        access_log /var/www/html/example/access.log;

        error_log /var/www/html/example/error.log;



    location / {

        # First attempt to serve request as file, then

        # as directory, then fall back to displaying a 404.

        try_files $uri $uri/ /index.php?$args;

    }



    # pass PHP scripts to FastCGI server

    #

    location ~ .php$ {

        include snippets/fastcgi-php.conf;

    #

    #   # With php-fpm (or other unix sockets):

        fastcgi_pass unix:/var/run/php/php7.2-fpm.sock;

    #   # With php-cgi (or other tcp sockets):

    #   fastcgi_pass 127.0.0.1:9000;

    }



    # deny access to .htaccess files, if Apache's document root

    # concurs with nginx's one

    #

    location ~ /.ht {

        deny all;

    }



    listen [::]:443 ssl ipv6only=on; # managed by Certbot

    listen 443 ssl; # managed by Certbot

    ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem; # managed by Certbot

    ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem; # managed by Certbot

    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot

    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot

}



##### BEGIN PHPMYADMIN CONFIG    #####

server {

    root /var/www/html/phpmyadmin;



    index index.php index.html index.htm index.nginx-debian.html;



    server_name phpmyadmin.example.com;



    location / {

        # First attempt to serve request as file, then

        # as directory, then fall back to displaying a 404.

        try_files $uri $uri/ /index.php?$args;

    }



    # pass PHP scripts to FastCGI server

    #

    location ~ .php$ {

        include snippets/fastcgi-php.conf;

    #

    #   # With php-fpm (or other unix sockets):

        fastcgi_pass unix:/var/run/php/php7.2-fpm.sock;

    #   # With php-cgi (or other tcp sockets):

    #   fastcgi_pass 127.0.0.1:9000;

    }

}

###### END OF PHPMYADMIN CONFIG #####



server {

    if ($host = www.example.com) {

        return 301 https://$host$request_uri;

    } # managed by Certbot





    if ($host = example.com) {

        return 301 https://$host$request_uri;

    } # managed by Certbot



    listen 80 ;

    listen [::]:80 ;



    server_name example.com www.example.com

    return 404; # managed by Certbot

}

I solved my problem and I am going to list out the steps I took to resolve the issue as future reference for others:

NGINX Configuration

The nginx configuration I tried initially was correct (as posted in the question).

Adding a CNAME record into DNS entries

This was the major missing piece. I added a CNAME entry into my DNS dashboard as follows:

Type: CNAME Name: phpmyadmin Value: example.com TTL: 3600 (can also set as automatic)

Expanding SSL Certificate

I use certbot for the SSL certificate, and I had to regenerate it to include the domain in the certificate.

sudo certbot --nginx -d example.com -d www.example.com -d phpmyadmin.example.com

During this step, certbot can take care of the nginx configuration to redirect HTTP traffic to HTTPS.

Reload NGINX service

Reloaded the new configuration: sudo service nginx reload

And verified the service status: sudo service nginx status

Everything is working well now.