[develop] Fix DCV on Ubuntu 22.04+ by disabling Wayland

CHANGELOG.md

@@ -14,6 +14,7 @@ This file is used to list changes made in each version of the AWS ParallelCluste
    and achieve better performance at scale. 
 - Load kernel module `drm_client_lib` before installation of NVIDIA driver, if available on the kernel.
 - Reduce dependency footprint by installing the package `sssd-common` rather than `sssd`.
+- Disable Wayland protocol in GDM3 for Ubuntu 22.04+ to force the use of Xorg on GPU instances running without a display.
 - Upgrade Slurm to version 24.11.7 (from 24.11.6).
 - Upgrade Pmix to 5.0.9 (from 5.0.6).
 - Upgrade libjwt to version 1.18.4 (from 1.17.0) for all OSs except Amazon Linux 2.

cookbooks/aws-parallelcluster-platform/resources/dcv/partial/_ubuntu_common.rb

@@ -82,6 +82,62 @@ def optionally_disable_rnd
     end
   end
 
+  # Disable Wayland in GDM to ensure Xorg is used
+  # This is required for Ubuntu 22.04+ where Wayland is the default
+  # Without this, GDM won't start Xorg on headless GPU instances
+  def disable_wayland
+    bash 'Disable Wayland in GDM' do
+      user 'root'
+      code <<-DISABLEWAYLAND
+        set -e
+        if [ -f /etc/gdm3/custom.conf ]; then
+          sed -i 's/#WaylandEnable=false/WaylandEnable=false/' /etc/gdm3/custom.conf
+          # If the line doesn't exist at all, add it under [daemon] section
+          if ! grep -q "^WaylandEnable=false" /etc/gdm3/custom.conf; then
+            sed -i '/\\[daemon\\]/a WaylandEnable=false' /etc/gdm3/custom.conf
+          fi
+        fi
+      DISABLEWAYLAND
+    end
+  end
+
+  # Override allow_gpu_acceleration to disable Wayland before starting X
+  def allow_gpu_acceleration
+    # Update the xorg.conf to set up NVIDIA drivers.
+    # NOTE: --enable-all-gpus parameter is needed to support servers with more than one NVIDIA GPU.
+    nvidia_xconfig_command = "nvidia-xconfig --preserve-busid --enable-all-gpus"
+    nvidia_xconfig_command += " --use-display-device=none" if node['ec2']['instance_type'].start_with?("g2.")
+    execute "Set up Nvidia drivers for X configuration" do
+      user 'root'
+      command nvidia_xconfig_command
+    end
+
+    # dcvgl package must be installed after NVIDIA and before starting up X
+    # DO NOT install dcv-gl on non-GPU instances, or will run into a black screen issue
+    install_dcv_gl
+
+    # Disable Wayland to ensure GDM starts Xorg
+    disable_wayland
+
+    # Configure the X server to start automatically when the Linux server boots and start the X server in background
+    bash 'Launch X' do
+      user 'root'
+      code <<-SETUPX
+      set -e
+      systemctl set-default graphical.target
+      systemctl isolate graphical.target &
+      SETUPX
+    end
+
+    # Verify that the X server is running
+    execute 'Wait for X to start' do
+      user 'root'
+      command "pidof X || pidof Xorg"
+      retries 10
+      retry_delay 5
+    end
+  end
+
   def post_install
     # ubuntu-desktop comes with NetworkManager. On a cloud instance NetworkManager is unnecessary and causes delay.
     # Instruct Netplan to use networkd for better performance

cookbooks/aws-parallelcluster-platform/test/controls/dcv_spec.rb

@@ -318,3 +318,27 @@
     end
   end
 end
+
+control 'tag:config_dcv_xorg_running_with_x11_session_type' do
+  title 'Check that Xorg is running and GDM is using X11 session type (not Wayland)'
+  only_if do
+    !os_properties.on_docker? &&
+      instance.head_node? &&
+      instance.dcv_installed? &&
+      node['cluster']['dcv_enabled'] == "head_node" &&
+      instance.graphic? &&
+      instance.nvidia_installed? &&
+      instance.dcv_gpu_accel_supported?
+  end
+
+  describe 'Xorg process should be running' do
+    subject { command('pidof Xorg || pidof X') }
+    its('exit_status') { should eq 0 }
+    its('stdout') { should_not be_empty }
+  end
+
+  describe 'GDM should be using X11 session type, not Wayland' do
+    subject { command("loginctl show-session $(loginctl | grep gdm | awk '{print $1}') -p Type 2>/dev/null | grep -i x11") }
+    its('exit_status') { should eq 0 }
+  end
+end