Fritz!Box & Ubuntu: Expose URL in LAN with Apache Httpd and Bind

I hope someone can help me with this - I thought - simple task.

Situation:

On my private LAN I run an Internet-Router ("Fritz!Box") and a Raspberry Pi with Ubuntu 20.04 LTS on it. I developed a little Spring Boot Web-App for private purposes that I only want to use in my LAN (or maybe reach via VPN from the outside). The native URL of the Web-App is "http://ubuntu:8080", because my Raspberry is called "ubuntu" and the app runs on a Tomcat-Server. Now I want to expose an URL like e.g. "http://thats-my.app" inside the LAN and use it as base URL for the app. For the moment, curl on the ubuntu can reach it, my other PC can't.

Even better would be a FQDN "http://wow.thats-my.app" (with a subdomain) so I can use the same domain and top-level-domain for all apps, and only vary the subdomain, like "http://super.thats-my.app" and so on.. Disclaimer: Since I work via SSH all configuration is done Terminal-only. Please consider that I don't use the Desktop Surface of Ubuntu.

Thank you in advance for your time and hopefully for your help!

Here are the setups I did to the ubuntu system. What is not shown here is commented out!:

ufw

Status: active

     To                         Action      From
     --                         ------      ----
[ 1] 9090/tcp                   ALLOW IN    Anywhere                   # UBUNTU-COCKPIT
[ 2] 3306/tcp                   ALLOW IN    Anywhere                   # MYSQL
[ 3] Apache Full                ALLOW IN    Anywhere                   # :80,:443
[ 4] Bind9                      ALLOW IN    Anywhere                   # :53
[ 5] OpenSSH                    ALLOW IN    Anywhere                   # :22
[ 6] 8080:8090/tcp              ALLOW IN    Anywhere                   # TOMCAT
[ 7] 9090/tcp (v6)              ALLOW IN    Anywhere (v6)              # UBUNTU-COCKPIT
[ 8] 3306/tcp (v6)              ALLOW IN    Anywhere (v6)              # MYSQL
[ 9] Apache Full (v6)           ALLOW IN    Anywhere (v6)              # :80,:443
[10] Bind9 (v6)                 ALLOW IN    Anywhere (v6)              # :53
[11] OpenSSH (v6)               ALLOW IN    Anywhere (v6)              # :22
[12] 8080:8090/tcp (v6)         ALLOW IN    Anywhere (v6)              # TOMCAT

/etc/hosts

127.0.0.1 localhost.localdomain localhost
127.0.1.1 ubuntu
127.0.1.1 thats-my.app

(--> no entries for IPv6)

/etc/apache2/sites-available/thats-my.conf

<VirtualHost *:80>
        ServerName thats-my.app
        ServerAlias thats-my
        ProxyRequests Off
        <Proxy *>
                Order deny,allow
                Allow from all
        </Proxy>
        ProxyPreserveHost On
        ProxyPass               / http://localhost:8080/
        ProxyPassReverse        / http://localhost:8080/
</VirtualHost>

--> Symbolic link to sites-enabled directory

/etc/bind/named.conf.local

zone "thats-my.app" IN {
        type master;
        file "/etc/bind/forward.thats-my.app.db";
        allow-update { none; };
};

zone "178.168.192.in-addr.arpa" IN {
        type master;
        file "/etc/bind/reverse.thats-my.app.db";
        allow-update { none; };
};

/etc/bind/named.conf.options

options {
        directory "/var/cache/bind";
        forwarders {
        1.1.1.1;
        1.0.0.1;
        8.8.8.8;
        8.8.4.4;
        };
        dnssec-validation auto;
        listen-on-v6 { any; };
        allow-query { any; };
};

/etc/bind/forward.thats-my.app.db

$TTL    604800
@       IN      SOA     ns1.thats-my.app. admin.ns1.thats-my.app. (
                              5         ; Serial
                         604800         ; Refresh
                          86400         ; Retry
                        2419200         ; Expire
                         604800 )       ; Negative Cache TTL
;
@       IN      NS      ns1.thats-my.app.
ns1     IN      A       192.168.178.23

/etc/bind/reverse.thats-my.app.db

$TTL    604800
@       IN      SOA     thats-my.app. admin.thats-my.app. (
                              4         ; Serial
                         604800         ; Refresh
                          86400         ; Retry
                        2419200         ; Expire
                         604800 )       ; Negative Cache TTL
;
@       IN      NS      ns1.thats-my.app.
ns1     IN      A       192.168.178.23
23      IN      PTR     ns1.thats-my.app.

--> input to Terminal:

sudo systemctl restart named
sudo systemctl restart apache2
sudo systemctl restart bind9

--> DNS Configuration in the Router

Set DNS IPv4 IP to 192.168.178.23 (primary and secondary)

Set DNS IPv6 IP to IPv6 address of the ubuntu machine (primary and secondary)

Here's what I got:

On the local Ubuntu-Server

$ curl thats-my.app -> OK
$ dig thats-my.app -> status: NOERROR   *but*  SERVER 1.1.1.1#53 ???
$ dig thats-my.app @127.0.1.1 -> "connection timed out!"
$ dig thats-my.app @192.198.178.23 -> "connections timed out!"

On the LAN Windows-PC PowerShell

curl thats-my.app -> cannot be resolved

On the LAN Windows-PC Chrome Browser

http://thats-my.app -> Website unreachable / DNS_PROBE_FINISHED_NXDOMAIN

If you look at the "dig" - results it seams to me that Bind9 doesn't work right here. What do you think?

Thanks!