I guess you did not read the link I posted initially. When you set up a firewall on a machine to block all incoming traffic on all ports except 443 and then run docker compose exposing port 8000:8000 and put a reverse proxy like caddy/nginx in front (e.g. if you want to host multiple services on one IP over HTTPS), Docker punches holes in the iptables config without your permission, making both ports 443 and 8000 open on your machine.
@globular-toast was not suggesting an iptables setup on a VM, instead they are suggesting to have a firewall on a totally different device/VM than the one running docker. Sure, you can do that with iptables and /proc/sys/net/ipv4/ip_forward (see https://serverfault.com/questions/564866/how-to-set-up-linux...) but that's a whole new level of complexity for someone who is not an experienced network admin (plus you now need to pay for 2 VMs and keep them both patched).
Either you run a VM inside the VM or indeed two VMs. Jumphost does not require a lot of resources.
The problem here is the user does not understand that exposing 8080 on external network means it is reachable by everyone. If you use an internal network between database and application, cache and application, application and reverse proxy, and put proper auth on reverse proxy, you're good to go. Guides do suggest this. They even explain LE for reverse proxy.
@globular-toast was not suggesting an iptables setup on a VM, instead they are suggesting to have a firewall on a totally different device/VM than the one running docker. Sure, you can do that with iptables and /proc/sys/net/ipv4/ip_forward (see https://serverfault.com/questions/564866/how-to-set-up-linux...) but that's a whole new level of complexity for someone who is not an experienced network admin (plus you now need to pay for 2 VMs and keep them both patched).