OpenShift 4.11 TLS handshake timeout on oc login

Finally after OKD 3.11 support has ended I’ve decided to try 4.x releases. I found that there is quite nice installation assistant available on (Red Hat Hybrid Cloud Console). So I tried it and installed new cluster on my dedicated hardware. I set up all things as usual which is project, token and GitLab runner. Unfortunately on oc login command there was error “TLS handshake timeout”. Investigation was quite broad including replacing docker base images, downloading custom oc binary, doing regular networking diagnostics etc. In the end it turned out that there was issue with MTU and as it is setup in Hetzner on vSwitch this setting is a must have. So…. go to /lib/systemd/system/docker.service and edit it:

ExecStart=/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock --mtu=1400

Crucial is to set mtu in the end. After this you reload systemctl and restart docker service. Now you should be able to login using oc binary either provided by regular origin-cli image or manually downloaded binary on any other base system.