Why can't I connect to any container from outside localhost?

General
1

I have Docker server setup on a Ubuntu headless server on my home network. Docker works great. I have collabora running and now portainer. Collabora runs through an Apache proxy under Owncloud. Portainer exposes port 9443 to all networks (0.0.0.0:9443). But if I try to connect to Portainer from my Windows PC on the same network, it fails. If I ssh to the server from Windows and tunnel port 9443 from my Windows localhost, it connects to Portainer.

The firewall on the server exposes port 9443. And if I run nmap localhost -p 9443 on the server I can see its open and listening. If I run netstat I get:

netstat -lntp | grep 9443
tcp 0 0 0.0.0.0:9443 0.0.0.0:* LISTEN 719748/docker-proxy
tcp6 0 0 :::9443 :::* LISTEN 719754/docker-proxy

Looks good to me, yet no machine outside localhost can access any container on the server.

HELP!

2

What does that mean? “Could not connect”, “404 not found”, any other error message?

3

Thank you for your reply!!

From a web browser to “https://172.20.21.2:9443” - the connection times out.
If I telnet to that same ip and port from my Windows PC, the connection times out also.
Otherwise - all native applications on the server are accessible from my lan, https, imap, ssh, etc.

4

Got it! - specifically for a container that is started with the docker run command line, I needed to add the option
“–network host” as part of the start string. So the whole string that used to look like this:

docker run -d -p 8000:8000 -p 9443:9443 --name=portainer --restart=always -v /var/run/docker.sock:/var/run/docker.sock -v portainer_data:/data portainer/portainer-ce:2.21.0

Now looks like this instead:

docker run -d --network host --name=portainer --restart=always -v /var/run/docker.sock:/var/run/docker.sock -v portainer_data:/data portainer/portainer-ce:2.21.0

And this connects it to my local network instead of just to the local machine running docker.