[SOLVED] Cannot access forwarded port on container from other containers in Docker network

Issue

Cannot access forwarded port on container from other containers in Docker network

On the Docker container A executed command to open the ssh tunnel to forward 3306 port from remote MySQL server to container.

ssh -4 -NL 3306:127.0.0.1:3306 "${SSH_USER}@${MONOLITH_IP}"

It's accesible from inside container A.

telnet 127.0.0.1:3306
Connected to 127.0.0.1:3306

netstat -lnt
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State   
tcp        0      0 127.0.0.1:3306          0.0.0.0:*               LISTEN   

But it's not accessible from container B

telnet A 3306
telnet: can't connect to remote host (172.17.0.5): Connection refused

Both container inside same network and running on alpine image.

Commands:

• ssh -4 -NL 3306:127.0.0.1:3306 "${SSH_USER}@${MONOLITH_IP}" (on container A)
• telnet 127.0.0.1:3306 (on container A)
• telnet A:3306 (on container B)

Expectation:

Successful connection from container B to the forwarded port on container A (MySQL server).

Actual Result:

telnet A:3306 (on container B) returns telnet: can't connect to remote host (172.17.0.5): Connection refused

despite verifying network connectivity, port availability

Solution

The SSH tunnel is bound to the loopback interface (127.0.0.1) inside container A, which means it is only accessible from within that container.

To make the forwarded port accessible to other containers within the same Docker network, binding the SSH tunnel to the container's IP address or 0.0.0.0 (all network interfaces) instead of 127.0.0.1.

ssh -4 -NL 0.0.0.0:3306:127.0.0.1:3306 "${SSH_USER}@${MONOLITH_IP}"

Answered By - Illya Skidanov

Answer Checked By - Terry (WPSolving Volunteer)