Gitlab CI Debug terminal fails to connect with GCP

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Describe your question in as much detail as possible:
We have Google Cloud instance running the ci-runner and the jobs run successfully.
However after setting up the debug ports (as following)

[session_server]
  listen_address = "[::]:8093" #  listen on all available interfaces on port 8093
  advertise_address = "runner-host-name.tld:8093"
  session_timeout = 1800

We are only seeing a black screen (nothing on the screen) when we click Debug.

  • What are you seeing, and how does that differ from what you expect to see?
    From runner logs, we have seen seeing
Oct 30 19:05:12 instance-group-1-1wtm gitlab-runner[16539]: ERROR: Failed to connect to terminal                builds=0 error=timeout for waiting for build container uri=/session/71ffe0e024ca602727e648b4c90dc8a3b718ac6b699a6076e9eec1105a72c672/exec
Version:      13.5.0
Git revision: ece86343
Git branch:   13-5-stable
GO version:   go1.13.8
Built:        2020-10-20T12:05:19+0000
OS/Arch:      linux/amd64
  • Add the CI configuration from .gitlab-ci.yml and other configuration if relevant (e.g. docker-compose.yml)

  • What troubleshooting steps have you already taken? Can you link to any docs or other resources so we know where you have been?

Thanks for taking the time to be thorough in your request, it really helps! :blush: