Moving to a prebuilt CentOS 7 docker image

Author: weegeekps

.github/actions/action.yml

@@ -6,7 +6,7 @@ inputs:
     required: true
 runs:
   using: 'docker'
-  image: '../../docker/CentOS7.Dockerfile'
+  image: '../../docker/CI.Dockerfile'
   # Tell Conan to look for or create its build folder (.conan) in the repository's root directory
   env:
     CONAN_USER_HOME: $GITHUB_WORKSPACE

docker/CI.Dockerfile

@@ -0,0 +1,5 @@
+FROM cesiumgs/omniverse-centos7-build:2023-08-29
+
+WORKDIR /var/app
+
+ENTRYPOINT ["/bin/bash"]

docker/CentOS7.Dockerfile

@@ -1,3 +1,5 @@
+# This is used to generate the image with dependencies that CI.Dockerfile relies on.
+# For instructions for deploying this, check docs/release-guide/push-docker-image.md.
 FROM centos:7
 
 RUN yum update -y -q

docs/release-guide/push-docker-image.md

@@ -0,0 +1,49 @@
+# Pushing the Docker Image for CentOS 7 builds.
+
+We use a docker image for our CentOS 7 builds that contains all of our build dependencies, so we don't have to build the image from scratch on each build. This document outlines how to build and push this to Docker Hub.
+
+## Installing Docker
+
+Install [Docker Desktop](https://docs.docker.com/desktop/install/ubuntu/). You will need a license for this and access to our account.
+
+On Linux, docker is run as root. To avoid the requirement for `sudo`, you should add your user to the `docker` group:
+
+```shell
+sudo usermod -aG docker $USER
+```
+
+## Building the container
+
+Confirm that you have push access to the [container repo](https://hub.docker.com/r/cesiumgs/omniverse-centos7-build).
+
+### Log in
+
+Log into docker using:
+
+```shell
+docker login
+```
+
+### Build the docker image
+
+After making your changes to the docker file, execute:
+
+```shell
+docker build --tag cesiumgs/omniverse-centos7-build:$TAGNAME -f docker/CentOS7.Dockerfile . --no-cache
+```
+
+You should replace `TAGNAME` with the current date in `YYYY-MM-DD` format. So if it's the 29th of August, 2023, you would use `2023-08-29`.
+
+### Push the image to Docker Hub
+
+The build will take some time. Once it is finished, execute the following to push the image to Docker Hub:
+
+```shell
+docker push cesiumgs/omniverse-centos7-build:$TAGNAME
+```
+
+Again, you should replace `$TAGNAME` with the current date in `YYYY-MM-DD` format. So if it's the 29th of August, 2023, you would use `2023-08-29`.
+
+### Update CI.Dockerfile
+
+The `docker/CI.Dockerfile` file is used as part of the CentOS build step in our GitHub actions. You will need to update the version of the Docker image used to the tagged version you just uploaded.