How to debug port-forwarding-related connection issues with Gateway remote development

Problem

Port forwarding is an essential requirement for connecting to and running an IntelliJ IDE in remote development mode. Sometimes it is not obvious what causes the following message:

The Host Doesn't Meet the Minimal Requirements. The SSH port forwarding check failed. A client might not be able to connect to the remote backend. It could be due to some configurations, such as the SSH server configuration or firewall rules.

Resolution

Usually, it means that AllowTcpForwarding yes is not applied in the remote SSH server config (/etc/ssh/sshd_config), opening ports is prohibited, or other firewall restrictions are applied (troubleshooting guide). If you still experience issues, you can use this method to debug:

1. Connect to your server with SSH and manually invoke the command that opens a port for listening. It will show the port it uses. The exact go-worker name might be different. Example:

spmart@d1e1c62c23e4:~$ ~/.cache/JetBrains/RemoteDev/remote-dev-worker/remote-dev-worker_37fb36fac7f67b3ce58cfb3354f402e0b6564732bba476a358f9f19dafd5db17 port-forwarding-test
36129

2. Open a new terminal and forward the port from the previous step like this: ssh -L <PORT>:localhost:<PORT> <SSH-CONNECTION-STRING>. Example:

RS-UNIT-0030:~ spmart$ ssh -L 36129:localhost:36129 rd-docker-gateway

3. Open another terminal and do echo "HELLO" | nc 127.0.0.1 <PORT>. The host should answer with ACK. Example:

RS-UNIT-0030:~ spmart$ echo "HELLO" | nc 127.0.0.1 36129
ACK

Note: Not applicable to connections established with the JetBrains Toolbox app.