Added headless rendering tutorial

tutorials.md.in

@@ -38,6 +38,7 @@ Ignition @IGN_DESIGNATION_CAP@ library and how to use the library effectively.
 * \subpage test_fixture "Test Fixture": Writing automated CI tests
 * \subpage spherical_coordinates "Spherical coordinates": Working with latitude and longitude
 * \subpage python_interfaces Python interfaces
+* \subpage headless_rendering "Headless rendering": Access the GPU on a remote machine to produce sensor data without an X server.
 
 **Migration from Gazebo classic**
 

tutorials/headless_rendering.md

@@ -0,0 +1,76 @@
+\page headless_rendering Headless Rendering 
+
+It is often desirable to run simulation on a remote computer, such as
+a computer managed by cloud provider, in order to paralellize work or access
+specific compute resources. Simulated sensors that require GPU access have
+historically been difficult to use on a remote computer due to OpenGL's
+X server requirement on linux systems. This issue can be resolved through
+installation and proper configuration of X, but the steps can be complex and
+error prone.
+
+An easier solution is through the use of [EGL](https://www.khronos.org/egl), which allows for the the creation of rendering surfaces without an X server. Ignition Gazebo has added support for EGL via the `--headless-rendering` command line option. Use of EGL is only available with OGRE2.
+
+Example usage:
+
+```
+ign gazebo -v 4 -s --headless-rendering sensors_demo.sdf
+```
+
+If you are using Ignition Gazebo as a library, then you can configure the
+server to use headless rendering through the
+`ServerConfig::SetHeadlessRendering(bool)` function. Make sure your SDF
+world uses OGRE2.
+
+## AWS Example
+
+This example will guide you through the process of launching and configuring
+an AWS GPU instance with Gazebo running headless. A GPU instance is
+recommended when sensors that require a render engine are used. It is
+possible to use a machine without a GPU, in which case OGRE will revert to
+software rendering. You can read more about [OGRE's EGL implementation
+here](https://www.ogre3d.org/2021/02/06/ogre-2-2-5-cerberus-released-and-egl-headless-support).
+
+1. Go to the [AWS EC2 service](https://console.aws.amazon.com/ec2)
+2. Click the `Launch Instance` button in the upper right.
+3. Select `Ubuntu Server` version 20.04 or greater from the AMI list.
+4. Choose a GPU enabled instance type, such as `g3.4xlarge`.
+5. Enable `Auto-assign Public IP` on the `Configure Instance Details` step.
+   This is not the best practice, but it simplifies this tutorial. 
+6. Add around 200GB storage to your instance on the `Add Storage` step.
+7. Enable ssh source `Anywhere` on the `Configure Security Group` step.
+8. Review and launch your instance. Make sure to setup a key pair in the
+   popup that appears after clicking `Launch`.
+    1. You can configure other options as needed. Review the [AWS
+   documentation](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/EC2_GetStarted.html) for additional help.
+9. Select the newly launched instance on the EC2 dashboard, and take note of
+   the `Public IPv4 address`.
+10. SSH into your new machine instance.
+  ```
+  ssh -i SSH_PEM_FILE_USED_DURING_LAUNCH ubuntu@EC_INSTANCE_PUBLIC_IP
+  ```
+12. Install Ubuntu drivers, which will install nvidia drivers:
+  ```
+  sudo apt-get update
+  sudo apt install ubuntu-drivers-common
+  sudo ubuntu-drivers install
+  ```
+13. Add the `ubuntu` user to the `render` group, which is required to access
+    to the dri interfaces.
+  ```
+  sudo usermod -a -G render ubuntu
+  ```
+14. Reboot the machine and log back in.
+  ```
+  sudo reboot
+  ```
+11. [Install Gazebo](https://ignitionrobotics.org/docs/latest/install).
+12. Run a Gazebo world that uses OGRE2 with camera sensors using headless rendering. This will enable EGL.
+  ```
+  ign gazebo -v 4 -s -r --headless-rendering sensors_demo.sdf
+  ```
+13. Check that simulation is producing sensor data by ssh'ing into the EC2
+    instance from a new terminal and echoing a sensor topic.
+  ```
+  ssh -i SSH_PEM_FILE_USED_DURING_LAUNCH ubuntu@EC_INSTANCE_PUBLIC_IP
+  ign topic -et /thermal_camera
+  ```