Workflow Runners

Runners are the machines that execute jobs in a GitHub Actions workflow. Runners are hosted by GitHub and what is available depends on the GitHub orgainizaion tier ($$$). Each workflow job must specify their runner instance type.

The runners is specified by runs-on: and can be chosen from this list of runner instances.

For DART's action_on_pull_request.yml workflow, the instance chosen is ubuntu-latest which loads an Ubuntu operating system on into your runner.

runs-on: ubuntu-latest                  # runner type
    container:                          # specifies a container to run on top of runner
      image: hkershaw/dart-dep:1.0      # uses dart-dep:1.0 container that is pulled from Dockerhub
      options: "--cap-add=SYS_PTRACE"   # nasty argument required for OpenMPI to work correctly in containers

At the time of writing, Linux-based runners have:

• 2 x84_64 CPU cores
• 7 GB of RAM
• 14 GB of local scratch storage

The pull request workflow also loads pre-built Docker container that is hosted on Dockerhub. The usage of a container here is for speed. The libraries that DART depend on, netcdf and mpi, are installed in the container. The recipes for DART Docker containers are stored in the DART-containers, while the pre-built container image is hosted and pulled from the Dockerhub repository hkershaw/dart-dep:1.0.