Continuing a Cylc 7 Workflow with Cylc 8

Does This Change Affect Me?

Read this if you have a partially complete Cylc 7 workflow that you want to continue, rather than start from scratch, with Cylc 8. Some cycling workflows, for example, may need to run expensive “cold start” tasks and incur a multi-cycle spin-up if started from scratch.


Cylc 8 cannot restart a Cylc 7 workflow in-place, and continuing in a new run directory involves some careful set up (below). So, if possible you should complete the run with Cylc 7.

To continue a Cylc 7 workflow with Cylc 8:

  1. Stop the Cylc 7 workflow at an convenient place

    • Typically the end of a cycle point, to simplify the continuation

  2. Install a new instance of the workflow from source, with Cylc 8

    • Adapt file paths to the new run directory structure, in workflow and task configurations

    • Note Cylc 8 does remote file installation when a job is first submitted to a platform

  3. Copy runtime files needed by upcoming tasks from the old to the new run directory

    • This could include external files installed by initial tasks at runtime

    • Note different files could be present on different job platforms

  4. Start the new Cylc 8 run at the appropriate cycle point or task(s) in the graph

    • Don’t reset the initial cycle point (in the flow.cylc or on the command line) to the start point of the Cylc 8 run. That would result in the “cold start” that this continuation procedure is designed to avoid. Instead use the --start-cycle-point option (or --start-task) with cylc play, to start at the right place within the graph.