DNS_PROBE_FINISHED_NXDOMAIN when serving multiple subdomains with nginx

Question

On our research project, we have an Ubuntu 20.04 LTS virtual machine running, which should serve via nginx multiple project related websites/apps on different subdomains.

The setup is supposed to be as following:

• maindomain --> redirecting to our project info site hosted by our university
• subdomain1.maindomain --> nextcloud for project management stuff served via nginx
• subdomain2.maindomain --> serving app1 via nginx proxy and gunicorn (for django)
• subdomain3.maindomain --> serving app2 via nginx proxy and express.js

What I did:

• Added the IP address of the server to the A record of our German domain hoster Strato.
• https://maindomain: configured nginx to redirect to university site

server {
        listen 80;
        listen [::]:80;

        listen 443      ssl http2;
        listen [::]:443 ssl http2;
        root /var/www/html;

        server_name maindomain;
        return 301 https://university-site;

        ssl_certificate /etc/ssl/wildcard.crt;
        ssl_certificate_key /etc/ssl/wildcard.key;
        ssl_trusted_certificate /etc/ssl/wildcard.crt;
        ssl_dhparam /etc/ssl/certs/dhparam.pem;
}

• configured nginx to serve nextcloud stuff in /etc/nginx/sites-available/subdomain1.maindomain

server {
        listen 80;
        #listen [::]:80;
        server_name subdomain1.maindomain;
        return 301 https://$server_name$request_uri;
}

server {
        listen 443      ssl http2;
        listen [::]:443 ssl http2;
        root /var/www/nextcloud;
        index index.html index.php /index.php$request_uri;
        server_name subdomain1.maindomain;

        ssl_certificate /etc/ssl/wildcard.crt;
        ssl_certificate_key /etc/ssl/wildcard.key;
        ssl_trusted_certificate /etc/ssl/wildcard.crt;
        ssl_dhparam /etc/ssl/certs/dhparam.pem;

... lot's of nextcloud related stuff ...
}

up to this point: everything is working fine for some time now

What I tried:

Now it was time to start deploying the next app on subdomain2.maindomain. In my naive thinking I thought just to copy /etc/nginx/sites-available/subdomain1.maindomain to subdomain2.maindomain and change "subdomain1.maindomain" to "subdomain2.maindomain" in the config file (of course: getting rid of all the nextcloud stuff, too).

First I experimented with just serving a static index.html page to see if everything is working:

server {
        listen 80;
        server_name subdomain2.maindomain;
        root /var/www/subdomain2;
        index index.html index.php /index.php$request_uri;
        # return 301 https://$server_name$request_uri;
}

• added a static index.html into /var/www/subdomain2
• restarted nginx (feels like a 1000 times actually... :-)) Now when I try to navigate to "http://subdomain2.maindomain" it throws the error: DNS_PROBE_FINISHED_NXDOMAIN

For testing purposes I added our IP address to the configuration /etc/nginx/sites-available/subdomain2.maindomain, resulting in:

server {
        listen 80;
        server_name subdomain2.maindomain IP_ADDRESS;
        root /var/www/subdomain2;
        index index.html index.php /index.php$request_uri;
        # return 301 https://$server_name$request_uri;
}

Now, when I browse to IP_ADDRESS the static index.html page is served just as expected, but browsing to subdomain2.maindomain still fails.

BTW: Another curiosity: on my Domainhoster I added a subdomain "subdomain2.maindomain" (which I didn't need todo for the other "subdomain1.maindomain"). In the A record I added the server IP_ADDRESS. Now when I head to subdomain2.maindomain nginx redirects to "subdomain2.maindomain/index.php" this loads nextcloud which gives me of course an trsuted_domains error. Why is nginx redirecting to nextcloud?

What can I do next? Thanks for any help!

Answer 1

Seems, like it really was I problem with the DNS Servers. After about 24h the subdomain worked just fine. Should have waited a bit longer...