Currently the Dockerfile.linux.testrunner Dockerfile is built on every Linux build leg in the official builds and CI. This Dockerfile is taking a significant amount of time to build. Approximately 1/3 of the build time. The Docker and Powershell parts of this Dockerfile could be built once and pushed to a Docker registry e.g. (https://hub.docker.com/r/microsoft/dotnet-buildtools-prereqs) and simply pulled in the build legs. This change could be flown to the other Docker repos that have this same testrunner Dockerfile.
Currently the Dockerfile.linux.testrunner Dockerfile is built on every Linux build leg in the official builds and CI. This Dockerfile is taking a significant amount of time to build. Approximately 1/3 of the build time. The Docker and Powershell parts of this Dockerfile could be built once and pushed to a Docker registry e.g. (https://hub.docker.com/r/microsoft/dotnet-buildtools-prereqs) and simply pulled in the build legs. This change could be flown to the other Docker repos that have this same testrunner Dockerfile.